Exactly one of these LG HG2 18650 batteries is fake. Which one do you think is most suspicious?
For the rest of this blog post, these cells will be displayed in this order, labeled Cell #1, Cell #2, Cell #3, and Cell #4.
Please take everything from this point on with a grain of salt. It is far from an absolute guide. Our observations are for a small selection of HG2 cells. Furthermore, with every new production batch that comes to market - things may change including markings, PVC, grooves, and so forth.
Ever since we posted a review of the LG HG2 battery, we have been asked the same question over and over- "how can I tell if my HG2 is fake?"
It is a good question to ask indeed, as we have identified a seemingly endless number of counterfeit HG2 cells on the market. It can also sometimes be very difficult to tell the difference, even for experienced purchasers.
Battery Bro is an American team in Asia. I recently stayed in Dongguan, China where I had the privilege of ordering things with Taobao. For those of you who don't know, Taobao is the largest e-commerce website in China, and well-known for the number of fake things.
Chinese 18650 wholesalers usually have two sources of revenue - their domestic sales (where they host a store on Taobao) and their international ones (selling via Alibaba, cold-emailing, and so forth). Ordering from a Taobao shop is an easy and anonymous way to verify supplier stock.
What counterfeiters will do to better cover their tracks is to make sure sample orders for buyers always contain authentic cells. And when you start ordering larger quantities they will start intermixing fake cells with real ones. This makes it quite difficult to identify fakes, and impossible for most overseas buyers.
On Taobao however, things are different. Suppliers will gladly sell fake cells with their arms wide open. Domestically there are far fewer repercussions and chances to be caught than when sending them through international customs.
So we anonymously purchased cells from as diverse a seller group as possible (all who are listed on Alibaba), and quickly landed fakes.
In this blog post we will take four different HG2 batteries that I think are characteristic of the overall stock on the open market. This will hopefully answer some important questions and help you identify whether yours is fake or authentic.
Remember, three of these batteries are genuine, and only one is a fake. If you want to know which one is fake right away, just scroll to the end where we provide a summary of our findings.
When I lay them down I can see that general characteristics of all the cells are the same. I am mainly looking at the positive terminal and seeing if there are any significant differences at a glance.
Underneath the positive terminal is the vent, and sometimes there are markings here which can help identify the cell. Markings near the vent can range from grooves on a certain number of sides to markings along the actual vent.
Unfortunately in this case I did not find any marks under the top-cap which will help us quickly identify fake HG2 batteries.
Here is a close-up of the top caps (positive terminals) of the cell.
All HG2 cells have four points of connection on their top cap.
Note that all their washers or insulator rings all have a textured, rather than a glossy finish.
You can run your fingernails and softly scratch them, or hold them up to a bright light and try to catch a gleam to characterize your own cell.
Here is a close-up of the texture on cell number 3. Notice how there is no shine and the texture is not very smooth.
Here is a picture of a confirmed fake HG2 cell we received from a vape shop owner. They emailed us, asking us to confirm whether they had received fakes, as these cells were showing a weak battery error in some mods, while other lower capacity cells were not.
The washer on this HG2 is shiny with a glossy finish. None of the genuine HG2 cells we have recently tested have a shiny washer so this should be a tell-tale red flag.
This is an image of the negative terminals of the cells.
Please note that the first two cells have already been charged and discharged at the point this picture was taken. This is so you can clearly see the difference that wear and tear has on new cells.
The steel tube scratches easily, and if there are an unusual number or an "organic" arrangement (ones were are clearly not created by robotic machinery at LG Chem - usually circular and limited to the center) of scratches, then you may be suspicious of a Grade B or Grade C (refurbished) cell.
If we move back to the top caps, we can observe the grooves which are formed by the connection between the positive and negative terminals. We can also see any other etching or grooves created by the machinery which assembles the steel tubes and cells.
In this image, I can clearly see a difference in Cell #2, which has grooves which extend further than the others. Please take a moment to observe the difference for yourself.
If one cell has a different length of grooves, perhaps the overall length is different. So let's measure all four cells and quickly check.
Cell #1 measures in at 65.4 mm.
Cell #2 has a height of 65.2 mm.
Cell #3 has also has a height of 65.2 mm.
And the last cell measures 65.3 mm. Looking at the HG2 spec sheet, the cells should measure as follows,
Official specification:
That means Cells #1 and #4 do not pass.* Although, the amount is very small (.1mm and .2mm respectively) - I believe it is due to measurement error on my own part, as all the cells seem to be measuring around .2mm too long.
*Thank you /u/SCalderwood for this correction
Now, let's also measure the cell's diameter and weight.
As you can see, all batteries have exactly the same diameter - 18.3mm
Compared to official specifications:
All the cells are the correct diameter.
The weight measurements are as follows:
Official HG2 specifications:
Since only a maximum weight is given by LG Chem, and none of the cells have serious variation we can say the weight tests pass for all cells.
Here is that image from the beginning of this article. If you noticed the color of the second cell seemed a little off, you are not alone. The color does indeed seem to be different.
The color of the battery comes from something called a PVC heat-shrink tube and the mostly neutral metal steel behind it.
There are a few different ways counterfeiters can make fake LG tubes, so let me quickly describe them. Creating high-quality PVC requires expensive tools. A PVC injection mould machine (just a small one) will cost upwards of $15,000, not to include the expertise, parts, and other materials required to run it.
It is for this reason I speculate that high-quality brown-colored PVC tubes are not coming from any low level 18650 battery traders. Brown PVC tubes that mimic those that LG produce are probably coming from two sources:
In all cases, the 18650 counterfeiters are purchasing the actual PVC rather than producing it themselves.
In scenario 2A, a counterfeiter could purchase a cheap rotogravure machine and print any text they want. But the quality might be low, and the other two options are more plausible for high-quality fakes.
Now, let's take a closer look at the color difference between the cells.
Try to notice the difference in color that Cell #2 exhibits in this shot.
The light-sources used in this photograph, along with the shadows and reflections from an uneven environment can all obscure the true colors of the cells. For this reason, you should take a look at the next shot, flip back and forth, and try to notice the difference.
Cell #2 seems more purple, or more red, than the other two doesn't it?
In this black light test, no abnormalities were detected.
For this test I have cut some PVC off of each cell and shined a very bright colorless light through each one. This is so we can now compare the color difference more accurately on a computer.
Please note, they look more red than brown now because of the amount of light penetrating the PVC (it's like when you add milk to your hot chocolate, the brown gets lighter). In this case, the brown hue on the PVC is created from mostly dark red tones, and the red tones have been brought out more with additional light.
On a black background, it is easier to pick up some of the differences in tone.
After digital expansion, you may compare them to each other, rather than the black or white backgrounds.
Cell PVC #2 is the outlier and seems to have the most distinct and vibrant red color. The other three PVCs all seem to have more blue and green pigment in them.
Using a black and white infrared filter, we can clearly now see that the PVC on Cell #2:
So basically, Cell #2 (the suspected fake) has more red in it. This increased red hue, mixed with the other colors, makes the cell appear more purple in real life.
I like to use a needle, as it lets me precisely remove the PVC without causing damage to the battery. A knife or larger instrument might easily scratch the cell.
I recommend you do not do this at home. If you do want to unwrap the cell yourself, you should choose a non-metal tool, like a ceramic knife or something else that will not conduct electricity.
You should also have a new PVC to replace it with immediately to prevent short-circuiting in your device, trash bin, or storage container.
Tip: When unwrapping a cell, always start at the negative terminal and work your way upwards. Avoid using any tools that conduct electricity at the positive pole of the battery. This goes for both unprotected cells, and when removing the PCB from a protected cell.
After the cells are unwrapped, there are clearly some differences:
Top-cap grooves:
Cell #1 has absolutely no markings whatsoever. This should normally raise a red-flag, however in this case it can be explained, and I will do so in a moment.
Cell #2 has the most markings. These markings present on all sides of the steel.
Cells #3 and #4 both have aesthetically identical markings, only slightly varying in alphanumeric value. Over the last several weeks we have seen this style of markings on genuine cells. Also, consider that the markings only vary slightly (I1022A vs. I11214) This adds confidence that these two cells are from the same production batch.
Unfortunately I must stress, that markings on steel can also be faked quite easily.
Why do I say this? Take a look at the following image:
Remember the vape shop who sent us photographs of their fake HG2 with the shiny washer / insulator ring? Here is another picture they sent us, this time of the markings.
The markings here are quite similar to the markings on Cells #3 and #4.
The difference then we can focus on, would not be the alphanumeric values of markings themselves but the quality of the markings. The marking on the cell shown above is faded, washed out, and unclear compared to those in Cells #3 and #4.
This is not an absolute indicator, but can be a form of corroborative evidence you may use.
There are two ways for markings to be faded, washed out, and unclear.
Markings on the steel are an excellent and-time tested way to add evidence to a cell's authenticity. That is because, it is always easier for a counterfeiter to purchase a blank steel tube and not print on them. Or to use a different battery. In some cases the counterfeiter will file off any markings, which will appear rough and slightly depressed from the original surface.
If you find any indication that markings have been filed off the surface of your 18650 battery, this is strong evidence of a counterfeit.
However, please remember that markings in most cases are to be taken with a grain of salt. Markings can not alone determine whether a cell is fake or not (as they can be faked quite easily themselves). They should only be used as a weak form of corroborating evidence.
There have been, for several months, a large number of HG2 batteries with no markings. They started appearing at a time when the HG2 was very scarce. The great scarcity of the HG2 was between the end of chinese new year (around February 15th) to late March 2016, and was caused by a number of factors.
During this period, nearly every Chinese supplier had run out, causing a shortage in other most other countries like the US.
However, around the same time, a large batch of HG2 batteries had been sent to Japan for a certain 18650 pack assembler, which ordered in excess. These cells in Japan were sent directly from South Korea to a specific manufacturer, were specially produced, and thus for their purpose never had any identification markings printed on them.
This particular manufacturer in Japan either by luck or by savvy sold off many of their cells at a time of scarcity, and thus the market has seen tens of thousands of LG HG2 batteries without any markings.
These batteries are authentic, Grade A, and yet had no markings.
February 1 | LG rumored to cease HG2 production for retooling (high percentage of rejects) |
February 7 - 13 | Chinese New Year |
February 15 | SK/HK Distributors cease HG2 sales |
March 15 | Unmarked HG2s appear |
March 25-30 | New HG2s appear |
April 1 | New IATA air shipping regulations take effect; air shipping of HG2s halts |
April 10-20 | HG2 supply dwindles again |
In my opinion, it is because it is a different cell. And I say that for a simple reason, and it's that we have seen these markings before, on a different cell manufactured by LG.
But I will return to this question a little later. First, let's see if there are any other abnormalities under the wrapping.
The top-caps all look the same, albeit the ring where the washer is meant to sit on Cell #2 is a bit cleaner and lighter than the other three cells.
Also, that the gap and shiny ring where the positive terminal and negative terminal meet is now confirmed to be notably larger.
I'm going to start calling Cell #2 the fake from this point on, although it is still unconfirmed I want to let you clearly know where the suspicion is. This is because we have identified three types of weak corroborating evidence:
Here you can observe the difference between the two 18650 batteries with enhanced sharpness.
Here is another close-up shot with enhanced sharpness.
Compare with Cell #3.
And remember the battery picture from the vape shop we got? The one with the shiny (not textured) washer? This is a photograph of the top-cap of that cell.
If we look closely at the metal where the washer would normally lay, it clearly looks cleaner. The genuine cells we are looking at have a much browner appearance here, while the fake ones have a more of a metallic steel color.
Take a moment to scroll back up and look at the more brownish color that Cell #3 exhibits here.
Another shot of the markings on Cell #3.
And the opposite end of HG2 Cell #3. Note the markings are scarce on this cell, and not seen all the way around.
Earlier I had said, I have seen markings such as the ones on Cell #2 before. Please take a look at the following images and judge for yourself:
On the left of this image is Cell #2, turned 360 degrees to show all of its markings.
On the right side is an unwrapped HE2 we did for a previous post. Can you notice the similarities?
Here it is, a little bit easier to compare the markings.
So could Cell #2 be an HE2 or HE4, rewrapped as an HG2? Would there be motivation for counterfeiters to do so?
There are two big reasons - availability and cost.
The cost difference between the LG HE2 vs the LG HG2 can be upwards to $1.00 USD, making the HE2 substantially cheaper. Since wholesale 18650 batteries are a commodity, and they are available on the open market, a price difference of up to a dollar is extremely significant to the profit margins of counterfeiters.
Furthermore the HE2 is a couple years older than the HG2, and is readily available on the market. There are no shortages for the HE2, and it is a highly liquid cell. Whereas, the HG2, even though they have become more available are still relatively scarce and seeing shortages.
The HE4 is slightly more expensive, and less available than the HE2.
Furthermore, if you are going to fake an HG2, what is the easiest cell to use? Another LG cell is - because its top cap is going to be identical or nearly identical (with four positive terminal connection points).
If you were going to use a Samsung, or Panasonic cell the top-cap would be a dead giveaway as they use a different number of connection points and styles.
The last point in the favor of the HE2-as-a-fake-HG2 hypothesis is that they are both 20A cells. The counterfeiter may not want exploding batteries (end-users discharging too much current) as this would draw unwanted attention., and thus choosing one with a similar maximum continuous discharge rating is favorable. The loss to the consumer, is one of 500mAh. (The HG2 is rated at 3000mAh, while the HE2 is rated at 2500mAh - both are rated at 20A max. discharge current).
It is for these reasons, that by visual inspection alone I can say with some degree of confidence that Cell #2 is probably fake, and finally that it may be a rewrapped HE2.
However, we can't be certain until we do some actual testing. So let's get to it!
The first thing we must do is rewrap all of the cells before testing them. Again, this is to prevent short-circuiting and should always be done. Unwrapped cells are dangerous and easy to short-circuit. We use a heat-gun, but a blow-dryer works well too.
We also have to spot-weld some tabs on the newly wrapped cells so we can attach alligator clips to them.
We are using a RePower battery charge and discharge station (AC 220 / 60V / 20amp) for these tests because it will accurately show us a discharge of up to 20 amps - which the HG2 is rated for.
A 20 amp discharge should quickly be able to tell us which of the cells is counterfeit.
Here we go! Charging up the first two cells.
First, we had to charge the cells fully. Both cells were charged at 3A, which is very fast for charging. There are two important differences to note. First, Cell #1’s voltage rises MUCH more quickly than Cell #2. Second, Cell #2 has about 500mAh less to charge than Cell #1. This suggests that Cell #2 has less overall capacity than Cell #1.
However, this could be due to different starting capacities for both cells. Perhaps one cell wasn’t discharged as fully as the other? Let’s move on to our first discharge test at 10A.
Aha! Cell #2 really does have less capacity than Cell #1! Cell #1 appears to have about 2700mAh of capacity, while Cell #2 has about 2200mAh. A 500 mAh difference… suspicious!
But if Cell #1 is an HG2, shouldn’t it discharge to 3000mAh? There are a few reasons you get less than 3000mAh here:
Another interesting tidbit is Cell #2’s enormous voltage sag. As soon as the discharge test begins, Cell #2’s voltage sinks immediately relative to Cell #1. Not only do you get less capacity - you get far less voltage throughout the discharge cycle.
For Cell #1, this test took about 16 minutes. Cell #2 took 13 minutes to fully discharge.
(For high-level battery geeks out there: the reason the charts begin at about 3.4 volts is that our testing equipment doesn’t sample quickly enough to capture the high-voltage discharge that occur immediately after testing begins.)
But voltage is only part of the story. As we all know, excessive heat is bad for 18650s. It reduces their performance and cycle life. How do the two cells stack up in terms of temperature?
This chart shows how the cells heated up throughout their 10A discharge cycle. Cell #1 has an early, if small lead, which quickly grows into an 8 degrees Celsius temperature difference. Cell #2 doesn’t heat up nearly as much. Does that make it a better cell? The most likely explanation: Cell #2 was running at a lower voltage, and for less time.
This chart is a little more complicated. On the X axis is the cell voltage at any time during the discharge cycle; on the Y axis is the cell’s temperature. We can see that even at the same voltage, Cell #2 has a much lower temperature. This is probably due to the fact that it spends much less time at low voltages and doesn’t have as long of a run-time.
Now that we’ve seen how the two cells perform - very differently - let’s move on to the 20A discharge tests. This is the king of high-drain battery tests: the only true way to see how high-drain cells stack up.
We introduced an older HG2 (Cell #3) for this test, which has been through about 30 discharge cycles, to see whether Cell #2 might just be an old HG2.
Now it’s becoming clear that Cell #2 is not an HG2. Both Cell #1 and Cell #3 show the right amount of capacity, a bit above 2500mAh: this is what you would expect from a 3000mAh nominal cell at 20A discharge. However, Cell #2 only ends up with about 2050mAh. This is consistent with a 2500mAh or 2600mAh rated cell discharging at 20A.
One thing to note is that you would normally expect a cell to have less capacity at 20A than at 10A. This was true for Cell #2, but Cell #1 showed the opposite effect. This may be caused by the fact that this was one of Cell #1’s first discharges; sometimes 18650s need a few discharge cycles before they perform at their full potential. This may also be because much more time elapsed between the two discharge tests for Cell #1 than for Cell #2. We will follow up on this with our own testing.
Another thing to note: Cell #2’s voltage sag is MUCH worse than in the 10A discharge test. Much, much worse. While Cell #1 and Cell #3 had basically the same shape in their discharge curve, and although Cell #3 underperformed voltage-wise, Cell #2 shows a much earlier, steeper voltage sag. This is the mark of a very poorly performing high-drain 18650.
Now let’s look at how the temperature charts stack up.
Once again, we see the same pattern of Cell #1 heating up more than Cell #2. However, this time the temperature difference is much smaller.
(The difference between starting temperatures is easily explainable. Both Cell #1 and Cell #2 were charged just prior to being discharged. Since Cell #1 was charging for longer - it has more capacity, after all - it started just a bit hotter than Cell #2. Cell #3 had been fully charged long before its discharge test.)
All three cells reached temperatures that would degrade performance, over the long term. But this is to be expected for a continuous discharge at 20A. Battery pack users, beware: just because a cell is rated for 20A doesn’t mean you can push it that hard throughout its discharge cycle! It will have a hugely detrimental effect on battery life.
These tests lead us to conclude that Cell #1 and Cell #2 are not the same.
Okay, so you probably notice that the 25R5 and HE2 end much earlier in their voltage curve than Cell #2. We used slightly different parameters to run those tests - the cutoff voltage was 2.75V rather than 2.5V. But by tracing their curves down, you can see that they end at roughly the same ending capacity:
Conclusion: Cell #2 is not a 25R5 or HE2, although it has roughly 2500mAh capacity.
The incredible voltage sag suggests that Cell #2 is not rated for 20A discharge. Although it did not heat up to dangerous temperatures, it did not perform as a 20A-rated 18650 should under these discharge conditions.
What’s going on here? There are two possibilities:
While there were definitely a few errors in the experimental setup here, it was sufficient to show that Cell #2 is indeed not an HG2.
We started our mission in 2014 to fight against fake and dangerous 18650 batteries. However, as we get better, so do counterfeiters. Therefore it is always necessary to stay one step ahead and dig deeper. As we have seen in this article, telling fake cells from genuine cells is getting more difficult - but where there is a will there is a way.
Cell #2 is a fake LG HG2.
Cell #2 is likely a Chinese-made cell.
I believe, based on the results of this article, that currently the easiest test to see whether your HG2 is real or fake is to ask the following questions:
Finally, can you characterize your cell's performance?
Add up as many of these indicators as you can, the more you can check-off, the more likely you have a fake HG2 - with actual performance always being the strongest form of evidence.
A charger like the VC2 can quickly tell you if a cell does not have the right capacity.
Thanks for reading!
If you find our results controversial, have questions, or have spotted something we haven't please let us know in the comments. If you have inspected your own HG2 cells, please post your findings below to help others which come across this information.
If you would like to use any of the images presented here on your own blog, website, or social media please feel free. All we ask is that you provide a link back to our website.
A special thanks to Daniel Tok from InnoVape who let us use his images of a fake HG2 for this blog post.
If you are interested in getting a quote from Battery Bro for guaranteed Grade A, authentic, HG2 batteries for your business please follow this link.
]]>This is a very long (10,000 word, 60 image) blog post transcribing a lecture by professor Jeff Dahn from Dalhousie University titled "Why do lithium-ion batteries die, and can they be immortal?"
Not only is Jeff at the top of his field (he seriously is one of the leading figures in lithium-ion batteries), he also has a knack for making complicated things simple. The subject at hand really is technical, but anyone should be able to follow along thanks to Jeff's incredible understanding of the subject matter.
Out of the many resources we have come across on Battery Bro, this lecture stands out as one of the best.
Unfortunately, the lecture has never been transcribed, and there are no lecture notes or presentation files available anywhere on the internet. The camera-man does not always focus on the slides, and having the information in text with static images brings many benefits. Therefor we have undertaken the rather gigantuous task of transcribing the whole lecture, and here it is for you.
If you would like to contact Jeff, you can:
After this lecture was made, Jeff joined Tesla Motors on an exclusive 5-year agreement which will start in June 2016. Read about it in Fortune - Meet Tesla's new weapon a battery scientist.
If you don't have time to read or watch the whole lecture, I will do my best at condensing the meat of the article in as little words as possible for you.
It's my pleasure to be here and thanks for coming.
This is a collaborative effort between a bunch of us at Dalhousie and researchers at 3M and Medtronic Energy and Component Center and E-One Moli Energy in Maple Ridge. And I would say this works been sorta going on since about 2008 roughly.
So here's a picture of the Tesla Model S Motor Trend Car in the year in 2013. It seats seven people... amazing car, really very beautiful. It's all-electric, with a 265 mile range between charges, and costs about eighty five thousand dollars. A lot of that cost is in the battery.
And one of the questions people have is, even though the battery comes with an eight year warranty - it's going to be very expensive to replace, and how long will it last?
What electric vehicle manufacturers and lithium-ion battery makers know is that lithium-ion batteries struggle when the temperature is hot. So this is gonna be perhaps problematic in hot climates.
The first issue with lifetime with lithium-ion batteries in electric vehicles has come up now. In October of 2012, Nissan Leaf buyers in Southern California and Arizona sued Nissan in a class action lawsuit. They accuse Nissan of concealing Leaf vehicles that have a design defect that causes them to prematurely lose battery life and driving range. (eg. the “thermal management defect”).
So these typed things you'll see on this slide in the next few slides are directly cut and pasted off of the lawsuit that you can get online. Nissan failed to disclose and/or intentionally omitted to reveal a design defect in the leaf called the thermal management defect.
Other electric vehicles equipped with lithium-ion batteries are equipped with active thermal management systems and the idea is to keep the temperature in the battery pack down. Nissan however opted not to include an active thermal management system in the Leaf.
Lack of an adequate active cooling system cause the batteries to suffer heat-related damage causing premature battery capacity loss. Especially for those vehicles in warm climates, which are losing over 27.5 percent battery capacity within the first one or two years of operation.
So that's not good. So this a course results in the reduction a driving range, and what I want to do is to tell you why this is happening, and what we can do about it. But you gotta have some knowledge of how temperature affects lithium-ion battery lifetime and white lithium ion batteries fail anyway.
[Minute 4:00]
So here is a graph taken from a lithium-ion battery manufacturer’s website for lithium iron phosphate based lithium-ion cells.
It just shows the capacity that the battery delivers as a function of its charge/discharge cycle. number for cells tested at:
But when you look at 60 degrees C, 500 cycles, you've only lost 10 percent of the capacity. And in Southern California and Arizona it's not sixty degrees C, and even if you're charging and discharging the battery once per day in your Nissan Leaf, you're only gonna go 300 cycles in a year.
So how the heck could you possibly be losing 27.5 percent of the capacity in the first year? Like, it doesn't make sense until you read the fine print, and the fine print is right here at the top. (+1.5C - 2.5C Cycling).
1.5 C means it was charged in about 40 minutes and this -2.5 see means it was discharged in about 20 minutes.
So each charge discharge cycle takes about an hour maybe a little more. So this entire task took about 500 hours or so.
Okay, so this experiment was done very rapidly in a little a little less than a month.
If you take the same exact cell which comes from a A123 (LiFePo4/Graphite), and you tested where you do a charge-discharge - the discharge takes 56 hours and a charge takes 56 hours (it’s the red curve). And you plot capacity versus cycle number, you can see the thing dies really fast in its cycle count.
So this blue data is the 60-degree data I showed you on the previous slide and the red data is what happens if you go much more slowly. The time a each cycle takes is much longer.
The the point is that you get a lot of capacity loss per cycle number when you go slow at high temperature because there's chemical reactions going on in the cell that are bad. And when you do charge discharge rapidly, all you're doing is beating the clock. You're beating the clock on these temperature-dependent times (time-dependent parasitic reactions.)
If you take the same data and plotted versus time, so here's the blue data for the cells cycling rapidly and here's the red for the cell cycling slowly, now they're showing more similar slopes. This really tells you that the time of exposure at high temperatures is very important to their failure.
And it shows that cells have to be cycled under realistic conditions to give a meaningful cycle and counter life determination.
Just as a point of interest, these type of batteries are not used by Tesla Motors in their vehicles. They’re used by Fisker and by GM in its Chevy Spark.
So lifetime evaluation of lithium-ion batteries is a very tough problem because if you want to demonstrate an eight year warranty, you have to test for eight years in real conditions or you have to think of something else to do.
So what the battery makers generally do is they hide in the sand and they do cycle testing.
They buy a whole bunch of chargers, and they just put cells on task for long periods of time. And it's like running sausages through a sausage factory - you don't learn very much while you're doing that.
In 2008, we decided to really bite the bullet and invest the time and a lot of resources to maybe figure something out. We built some very high precision electronics I'll tell you about that allow us to do om measurements in a short period of time that allow us to project battery lifetime on the scale of years.
Okay so I'm gonna talk to you about experiments made an a few different types of lithium based cells. I'll talk about cells that have lithium metal negative electrode and a graphite working electrode. This is to study the behavior of the graphite electrode.
And I'll talk to you about cells that are lithium metal negative and a lithium transition metal oxide positive electrode, and that's to study the behavior the positive. And then I'll talk to you about cells that have the graphite in the positive electrode.
This is about what a lithium-ion cell consists of. These are coin cells that we make in our laboratory, and a lot of the other things I'll tell you in the lecture are on commercial lithium-ion cells made specially for us by different companies. I'll talk about the results on those too.
So the first thing we have to do is understand how a lithium-ion battery works. Okay so here's a picture showing the positive electrode. A lithium transition metal oxide on an aluminum current collector. The graphite negative electrode is on a copper card collector.
These two electrodes are separated by an electrolyte that contains dissolved lithium ions. Each of these electrode materials is layered, and they’re each intercalation compounds and that means lithium atoms can reside between the layers, and they can be deintercalated and intercalated when the batteries are charging and discharging.
What's really important to recognize is the intercalation and deintercalation processes is incredibly benign that causes a structural change of about 3 percent volume change in the positive and about 10 percent in the negative. There's no structural degradation that takes place in these materials at all. The failure of the lithium-ion battery really has very little to do with structural degradation of the electrode materials during the charge discharge cycling.
When the lithium-ion battery is assembled, the negative electrode is graphite - the kind that would be in your pencil. The positive electrolyte is a lithium transition metal oxide that’s synthesized in the air at high temperature. It's stable in air. So both electrolyte materials are stable in air, you can build a battery in the open air.
[Minute 11:00]
As soon as you put it together and start to charge the battery, you force electrons in this sense to the right, the corresponding lithium-ion hops out into the electrolyte and moves to the graphite where it gets intercalated. That charges the lithium-ion cell.
Once the lithium ion cell is charged, now the lithiated graphite - graphite with lithium inside - is very reactive. It reacted like with lithium metal, and the lithium transition metal oxide with missing lithium is also very reactive. What happens is both are those real electrodes actually react with the electrolyte solution that they're in contact with.
And then you would say well then how do you make a battery that has any lifetime at all if the electrolyte reacts with the electrodes? But by luck and by chance, when the reaction occurs, the reaction products turn out to be... solid on the negative electrode. They form a passivating film that slows down and limits further reaction.
On the positive electrode a similar thing happens. So by luck these reaction don't destroy the battery. In fact they form passivating services that allow them to operate for many months.
It's the formation, or the presence of these parasitic reactions that are bad and lead to the the failure lithium-ion cells.
So when you do testing of a lithium-ion cell, this is what you normally do. Your discharge it and you charge it, and discharge it, charge it, etc. between fixed upper and lower voltage limits and you measure the capacity of the cell during charge/discharge cycling.
So the capacity when you're doing this experiment at constant current is very easy to calculate. It's the constant current times the time above the charge for the charge cycle, that gives you the charging capacity. The capacity of discharge is the current times the time of the discharge cycle, that gives you the discharge capacity.
[Minute 13:00]
For a perfect lithium-ion cell, the charge the cell delivers and the charge that you store in the cell during the charges should be exactly the same. So this ratio:
Coulombic efficiency - the ratio of charge the battery delivers to, that which you store should be exactly one.
But the point is because of the parasitic reactions between the electrode materials and the electrolyte, this coulombic efficiency is not exactly one.
If you could measure the coulombic efficiency really accurately, you could use it to tell the magnitude of the parasitic reactions going on into the cell. That's going to be the point of this lecture is what can you learn if you measure the coulombic efficiency really accurately about cell lifetime.
So we have to know a little bit about the electrolyte in these batteries. They’re typically carbonate organic carbonates like:
A typical battery electrolyte might be lithium phosphate hexa fluoride dissolved in a mixture of these solvents. The solvents are mixed because some of them have much lower boiling points and give good low temperature performance. Some of them form very good passivating layers on the negative electrode. So using a mixture tends to have benefits.
As I mentioned, when the graphite becomes intercalated with lithium and it's exposed to electrolyte, it reacts with the electrolyte and a film of reaction products form on the surface and it's called the solid electrolyte interphase or SEI.
This is a picture from a paper by Emanuel Peled showing the sort of structure of the SEI. It's a heterogeneous mass comprising inorganic and organic components. But as this thing forms, it slows down the reaction between the lithium in the carbon and the electrolyte solution.
So you can take a look at this reaction between the lithium and the graphite and the electrolyte solution by studying a lithium metal versus a graphite cell.
In this lower panel now I've plotted the voltage of a lithium graphite cell as you add lithium to the graphite and then remove it again - it goes back and the voltage comes up again. But if you notice, you don't come back to zero on the capacity axis.
That's because some of the lithium that you've transferred to the graphite side has reacted and formed the solid electrolyte interphase. Some of the components in that solid electorate interphase were lithium oxide, and lithium carbonate.
They trap lithium atoms. So when you come all the way back, the graphite is empty of lithium but some on the lithium that you added is in that SEI and doesn't come back.
As you charge and discharge repeatedly, this voltage curve keep shifting to the right - always.
That comes about because some of the lithium is being trapped in that SEI film. So in this inside panel I just show you what's happening at cycles 1, 5, 10, 15 and 20, to the top of charge and the bottom of discharge.
They keep moving to the right. The rate of motion slows down as the film gets thicker and more protective.
In the top panel here I'm plotting the discharge end-point capacity. So the point at the end of discharge as a function of the cycle number in the black dots.
You can see it increases rapidly and then starts to slow down. The top of charge has exactly the same behavior - it moves rapidly at the beginning and then starts to slow down.
As the film thickens and becomes more protective. We call this motion charge and discharge end-point capacity slippage. It’s called slippage because this is slipping to the right… so I’ll talk about slippage from time to time.
You can learn about these parasitic reactions by carefully keeping track of the end-points and how they slip.
The positive electrode shows a similar issue. So here's the positive electrode, and when that electrode gets charged the voltage goes quite high - 4.2, 4.3 volts versus lithium metal. It’s a very oxidizing condition. An electrolyte can be oxidized. I just show it schematically by electrolyte with a plus there, and the reason I show it like that is don't think anybody really knows what happens in detail.
Anyway then this oxidized electrolyte might migrate over to the negative, where it gets reduced and forms some film of reaction product. That's just one scenario that might happen.
Here we're gonna just look at a lithium metal versus a lithium transition metal oxide cell. Again that's being charged - thats removing lithium making the material more oxidizing, and add the lithium back, and it doesn't come all the way back to the axis
Every time you charge and discharge the curve keeps shifting to the right. More and more electrolyte gets oxidized and that oxidation of electrolyte causes the charge imbalance between charge and discharge.
The endpoints keep shifting to the right and unlike the negative electrode side, this shifting doesn't seem to slow down. It just keeps increasing.
So these reactions between the electrode materials and the electrolyte are bad. It's bad and temperature aggravates those reactions.
Just to remind you, these parasitic reactions that are going on in the cell - they’re bad - and by measuring the coulombic efficiency of the cell you can quantify the amount of parasitic reactions that are going on in the cell.
But you have to measure the coulombic efficiency very accurately because it's very close to one in good lithium-ion cells.
If you want lithium-ion cells that last 10,000 cycles for grid energy applications, it would need a coulombic efficiency of at least 99.99 percent. That means if you want to make statements about a lifetime of cells based on coulombic efficiency measures, you’ve got to measure at least to the fourth digit in accuracy and precision.
But charger systems that you buy can't do this. So these two guys here took on the challenge of building a device that could measure coulombic efficiency very accurately.
Aaron Smith is now at Tesla Motors in charge of their battery lifetime group, and he graduated in 2012. Chris is still my group are working on this project, and they've done a really nice job.
This is a picture the machine that they built. It’s a sixty channel high precision charger system. Each of these brown boxes that you see is a precision current supply that supplies current with five digits of precision to a cell under test. And the cell under test are housed in these temperature control boxes so that the temperature is very stable and you can measure the charge and discharge capacities very accurately.
Everything's computer-controlled. The currents that these things output, even though they're very accurate and stable, we still pass those currents through precision resistors at the top of these racks and measure the voltage on the precision resistors to keep track of the current really well.
With this device we can measure coulombic efficiency very accurately.
I'll just show you some simple experiments that teach you about the Nissan Leaf.
These are experiments done on commercially made, what are called 18650 sized cell. 18650 batteries are 18 millimeters in diameter by sixty five millimeters long. It’s the size of your finger roughly. Batteries like that are made at a rate of about 3 billion per year, and they're used in low-end laptop computers.
Here we are cycling the cells at 60 degrees C, so very hot, and we're measuring coulombic efficiency versus cycle number. Cells are being cycled at three different rates.
There are two cells being measured in each of these tests. I'll just draw your attention to the scale, the coulombic efficiency at the axis, the accuracy of the data, and the lack of scatter in most to the data.
Obviously if it takes two hundred hours for a cycle, you're going to get a data point every 200 hours in these bold crosses. If it takes 100 hours for a total cycle at C over 50 you get a data point every 100 hours.
You can notice that the coulombic efficiency of these cells depends on the charge/discharge rate. The reason for that is, it takes longer for a cycle, which means there is more time for the parasitic reactions to take place when you go slower.
If you instead plot the coulombic inefficiency which just one minus the CE (so just flip the data over) and then take a look carefully - you'll notice that the coulombic inefficiency scales 1 to 2 to 4 just like the cycle times do.
If you divide one minus the coulombic efficiency by the time of a cycle, all the data falls on a universal curve.
It’s telling you that the time of exposure is really the bad actor here in the failure of these cells at elevated temperature. Now these measurements can be used to rank all lithium-ion technologies.
I'll just show you some other measurements and it's a busy slide but easy to understand what you look at it.
[Minute 25:00]
There's data here for 36 cells.
In this panel (top-left) lithium cobalt oxide lithium-ion cells running at three different rates are being characterized, and it's one minus the coulombic efficiency over the time over cycle and it’s at 30 degrees C.
As we go from column to column we change to a nickel cobalt manganese lithium-ion battery [LiNiMnCo, NMC, or NCM] to iron phosphate lithium-ion battery [LiFePO 4, or LFP], and lithium manganese oxide lithium-ion battery. And you can look and say - well look at these universal curves… clearly parasitic reactions are worse in this technology. Then we’ve done the measurements at 40 degrees, 50 degrees, and 60 degrees C.
If you were going to select the lithium-ion cell for a hot climate, would you select this one? If you weren’t going to thermally manage it? Or would you select this one or that one?
What did Nissan select? Nissan selects a blend of fifty percent of this and fifty percent of that in their cells and so does GM in the Chevy Volt. Nissan does not temperature control the battery pack. Lots a parasitic reactions going on at elevated temperature is going to lead early cell failure. GM does temperature control their battery pack and their packs a lasting longer than the Nissan under high temperature conditions.
Fisker, are another poor choice.
And Tesla has selected chemistries like lithium cobalt oxide that are very good.
These precision coulometry experiments, you look at them this way and they tell you a lot about competing technologies. Whereas, you know, a battery maker or a tester without access to this data have to test for a long time to come to these kind of conclusions about the severity of the parasitic reactions of the different technologies.
Now I want to use this equipment to start talking about how lithium-ion fails, what are we going to do about it, and how are we going to make it better.
I want to talk about what are called electrolyte additives. Every lithium-ion cell that you use, be it in your phone or in your laptop or tablet or whatever it is - the manufacturer has put in the electrolyte - some chemicals like a secret sauce that improves the lifetime of that cell, and they’re called additives.
The most famous is vinylene carbonate and it causes less electrolyte oxidation on the positive electrode as I'll show you in the next few slides. People add additives that reduce the impedance of cells and limit gassing in cells.
They add wetting agents because they’re trying to feed them through the manufacturing process as fast as possible. You add the electrolyte to the cell, and it has to fill into these porous electrodes. To add a wetting agent does that quicker. But how does that impact the cell lifetime and all kinds of other things?
A typical lithium-ion cell might have five additives in it for various purposes. Here I'll just show you the impact a vinylene carbonate.
Here are lithium cobalt oxide graphite lithium-ion cells. They're being cycled with the high precision charging equipment so as you charge and discharge you can see the voltage capacity curve again shifting to the right. This is caused by parasitic reactions taking place, causing electrolyte oxidation at the positive electrode. The thing is slipping to the right.
The cell measured at 40 degrees C but if you add vinylene carbonate to the electrolyte... back... just stops. So you really impact that parasitic reaction a lot with 2 percent by weight of an electrolyte additive. The same thing happens at 60 degrees C, there's a huge improvement in the rate of electrolyte oxidation at the positive electrode side.
[Minute 30:00]
Here is some other data, this is for lithium cobalt oxide cells with no vinylene carbonate in the electrolyte 1 percent and 2 percent. And then lithium cobalt oxide cells charged to a lower voltage. And cells that have a nickel manganese cobalt positive electrode.
What just want to show you here is that when you look at the data you can see that even one percent of vinylene carbonate really stops that slippage of the voltage curve to the right.
The way that we look at these data is not to look at curves like this, but instead to plot the charge endpoint capacity versus cycle number. I'll show you that on the next slide.
So here are the same cells on the previous panel, the lithium cobalt oxide cells charged to higher voltage and lower voltage. We’re plotting the charge endpoint capacity in percent versus cycle number.
So there's two cells here in the crosses. There's no vinylene carbonate added and you can see the end point slipping like crazy to higher capacities. When you add vinylene carbonate, either one or two percent it is very much reduced.
If you look at the coulombic efficiency and look at the scale here, and look how repeatable the pair cells are, (these are commercially made cells) without vinylene carbonate, the coulombic efficiency is poor. With vinylene carbonate the coulombic efficiency is much better. With the nickel manganese cobalt positive electrode, without vinylene carbonate it’s a much better situation.
Why is that? I don't know. And adding vinylene carbonate improves the situation over here. But the real take-home message here is if you measure capacity versus cycle number - I defy you to tell the difference between these different electrolytes from these measurements. They all look exactly the same.
You know, and this is what traditional battery testing is all about. You try to tell what's going on from discharge capacity versus cycle number and you're forced to cycle to end-of-life before you can tell what's going on. Whereas these high-precision measurements can distinguish between good and less good very quickly.
So this is using your head, and that's just "sausage factory" you know.
We've done this a few times where we take our short term measurements collected over a period of a couple weeks, and then we take the cells, and we've put them on a charger and run them for long periods of time.
So this is twenty hours for every cycle, 120 cycles, so 2400 hours of testing. And we increase the temperature too so that we could distinguish more quickly the differences between the cells. But you can see over here the cells that are best.
The top one over here, and then these blue symbols are next, and they’re next here, and the black is worst, and the red is next. The point is the short term measurements bear out in the long term.
If you're somebody like me, and you're trying to make lithium-ion cells better, and you don't want to test for a long period of time, you do these high precision measurements. You can tell - does the electrolyte additive help or hinder what you trying to do?
Here is some data from Medtronic for cells that are implanted in the human body to run a pain relieval system. They have cells in the lab that have eight years of testing accumulated at 37 degrees C.
You can see six to eight cycles a day, twenty thousand cycles, eight years of testing at 37 degrees C. That's pretty impressive! Cells like this with nickel cobalt aluminum [LiNi0.8Co0.15Al0.05O2] are in the Tesla Motors vehicle. Tesla Motors uses technology that's at least this good. This is eight year old technology, the test started eight years ago, it has to be eight years old technology.
How do you make it better? Well do you want to test for eight years before you find out if it's better or not? So Medtronic is working with us to improve these cells, and what we do is we take their cells with different electrode additives that we and they specify, and we measure the coulombic inefficiency divided by the time of a cycle.
The data that I showed you on the previous slide is for the additive set in the blue box. We've identified additives that are much better than the one in the blue box. And Medtronic is taking the ones that at the bottom and sets them off for long-term cycling and they'll of course be better than the ones that, you know, that are already demonstrated after eight years of testing.
So the point is in a few weeks you can identify things that are way better than what is currently being used.
Now here comes the ultimate challenge for this method. That is that sometimes lithium-ion cells show this kind of failure that's incredibly insidious. These are nickel manganese cobalt [NMC] positive electrodes with graphite negatives.
Cells are cycling to an upper cut-off of 4.25 volts and they look really good. If you change the upper cut-off voltage to 4.35 volts they start out looking really good. Imagine this was in your car - you say “oh everything's great, I love it, I love it” then all of a sudden you can't even get out the driveway.
There is no way for a lithium-ion battery manufacturer to learn about when they get this rapid catastrophic failure except to cycle it until they get there. If this happens after three years or five years, you gotta you gotta go there to find it.
We believe that this roll over or catastrophic failure comes about because of electrolyte oxidation at the positive side.
There's no capacity fade significantly here at all.
Lithium is not getting consumed in SEI at the negative. By contrast what's happening is the electrolyte is getting oxidized, oxidation products moved to the negative, and they coat across the service of the negative and eventually shut the cell down.
Now, if you charge to a higher and higher voltage, you accelerate electrolyte oxidation. This catastrophic failure moves to lower and lower cycle numbers as you can see. The point of this is, this is a great test bed for our methods. Coulombic efficiency measurements should capture this and should be able to predict the onset of catastrophic failure.
We did an experiment with E1 Moli energy in Vancouver where they built one-hundred and sixty 18650 batteries for us. These cells had four cells of every type with different electrolyte additives in them. Cells were all the same except for electrolyte additives.
Electrolyte additives are listed up here [referring to legend].
VC is vinylene carbonate, VEC is vinyl ethylene carbonate. It really doesn't matter what these things are - the different electrolyte additives in use. The way the experiment went was we got to specify the electrode additives in 80 cells and they got to specify the electrolyte additives in the other 80 cells and they didn't even tell us what they were.
Their additives are are these numbers, whatever they might be, and our additives are these known things which I can tell you what they are but I'll tell you it doesn't matter for the purpose of this talk.
The point is - take a look at the first 50 cycles of data, look at the blown-up capacity scale, can you tell me which are these are gonna fail first? You can't! You have to cycle them to death.
We selected a design that will show this catastrophic failure, now I’ll describe to you how you design a cell to fail like that in a few minutes.
Well, I give you 100 cycles to look at. There are 100 cycles now - can you tell me which of these is going to last longest this year or which is going to fail first?
You can see one starting to drop out here now at the bottom.
So this is the problem - you're trying to improve lithium-ion batteries and you have to wait until the end of life before you know which is better... it's too slow.
[Minute 40:00]
How did the experiment go with those guys?
So this is what happened: the cells were manufactured and then they were shipped to us for cycling on our high precision charger. We also did some storage studies that I won't talk about.
They came to us and we gave them sixteen cycles on the high precision station and here I'm showing you data for five different electrolyte additive mixtures. Four of them are knowns, and 2UB means to unknowns blend B.
You can see the coulombic efficiencies on this scale vary. So FEC is worse and then VC, then VC + FEC then 2UB and then these triangles up here. Quite a variation. Then after we tested them - we don't have the resources to do all this long-term testing that takes a year or so - we sent them back to the manufacturer for their long-term testing.
The long-term testing was done at 2 amp discharge and 2 amp constant current constant voltage charge, so C-rate for the battery people. We continue the testing until the cells reached 1.6 amp hours.
On the blue boxes where the testing was done at the manufacturer. If you look here at the first 50 cycles, and you'd say well the diamonds are looking best and maybe the crosses. But when the cycling continues the crosses die first and the diamonds aren’t far after.
If you look at that high-precision cycling data - look at that - well the crosses should die first and they do and the diamond should die next and they do and the squares and circles and the triangles.
So it's really what you want, so how do you design a cell to make it do this?
If the reason the cell shows this dramatic rollover catastrophic failure is because electrolyte oxidation products migrate to the negative where they’re reduced and eventually shut down the negative electrode: what would happen if you really highly compact the graphite particles in the negative electrode?
Here is kind of a cartoon. This is a negative electrode, it's made of graphite particles. It's been highly compacted so the porosity is pretty small.
You’re cycling the cell, you’re getting electrode oxidation products to come across.
When they get over there they see a low potential service at the front of the electrode and they get reduced and form some solidified junk there.
The cell capacity is not going down very much, and you cycle some more and the layer of junk gets thicker and the pore openings start to gets closed off.
And you cycle so more and the pores ultimately become filled. Now it's very hard for the lithium ions to penetrate into the back of the electrode because it's blocked
Then lithium plating begins on the surface and the capacity dies.
That's what we believe happens, and when you take the cells apart at the end of life, you see a lot of evidence from lithium plating in certain parts of the electrode.
If you had a more porous negative electrode, what what happen then? Well you would get the same scenario but the pores don’t close.
If you make the same cells with less compacted negative electrodes they don't show the catastrophic failure - the failure looks like this (top-right graph).
But it's still bad for the electrolyte oxidation that is going on because you're losing electrolyte.
So let's go back to our scenario. Let's say that we need a certain amount of fill material to block these pores and let's say that on every charge discharge cycle, one minus the coulombic efficiency measures how much electrolyte oxidation products moved from one side to the other.
If you get this much material on every cycle, and you need a constant amount of material to block the pores, then one minus CE times the number of cycles to failure should be a constant.
This constant is going to be proportional to the thickness of the film needed to block those pores.
So what you need to do is plot a graph of number of cycles to failure versus 1 over 1-CE and see what you get.
So we did this. Here's the cycles to 1.6 amp hours versus 1/(1 - Coulombic Efficiency) and there’s a pretty decent straight-line agreement here for the electrolyte additives that we know what they are.
It looks pretty good. There are some of them off the line but really there are only two sets or three sets that are significantly off the line. It's pretty amazing nobody's ever done this kind of thing ever before.
If you look at the positive electrode by SEM, I just picked one of the cells with VEC and FEC. After 420 cycles it failed before the cycling, and after the cycling the positive electrode looks exactly the same.
If you look at the negative electrode before and after you can see the buildup of this film of reaction products on the surface of the negative. So the square region has been expanded over here you, and see all this gunk on the surface of the negative and that's what is leading to the failure of the cell.
What about their additives, where they fall on the graph? I showed you the additives that we specified. Now I’ve changed the scale because the battery manufacturers are a lot smarter than university professors.
That's where there's fall So you take a look at some of these things, their coulombic efficiencies are similar, you know, to these guys, but the cycle life is way better!
This 4UA and 5UA differ only by the addition of one additive which is additive number five. This has 1234, this has 12345. Look at that - incredible.
How does it work?
From 5UA to the control with no additives there's a 20-fold increase in cycle life just with a few percent of a few magic ingredients. That's amazing - how does it work? Why are these points off our line?
Well our model assumes that any oxidation products which go over to the negative forms solid products that block the service of the negative.
Maybe when these guys go over, they don't form solid reaction products, maybe they're liquids, or maybe they’re gases - who knows. But then it wouldn't build up this film of reaction products that block the negative. So it's pretty mysterious.
Here's a graph that kind of summarizes that experiment. This is a graph showing you coulombic efficiency as a function of the number of electrolytes added to the cell. So there were four cell types that had one electrolyte additive and 11 cell types that had two and 10 that had three and three they had four and only one that had five.
But you can see in general the coulombic efficiency gets better and better as you go. And the corresponding cycles to failure generally gets better and better as you go.
So somehow these additives are acting in synergy in some way to improve things.
Now if you read the academic literature on electrolyte additives, people study one additive at a time. Are they going to learn anything relevant? I don't know because you have to put a bunch of them in to really do well. If you're not trying to figure out how this works, you're crazy, because this is the easiest way to improve lithium-ion battery technology. It's a way to really improve it like crazy.
So people got interested in our methods - I was lucky to get an automotive partnership Canada grant with a bunch of credible partners. We've expanded our are high-precision charger facilities.
This system has a hundred channels that can do automotive scale lithium-ion cells and we're using it with GM and Magna to test their cells. This came operational in April 20th. It's a pretty nice system.
I want to tell you one last thing before we stop
Sometimes it's a problem working with industrial partners. You may know that if you've ever done it. Sometimes you would suggest an experiment and they say “we don't want to do that, it wastes our resources” and we say well the scientific value is important we must do it.
But our experiments on these high precision cyclers, you need very repeatable cells to be able to say “okay the difference between that cell and that cell is because of the electorate additives” and not because some graduate student made a crappy cell (or a professor made a crappy cell).
Yeah, my cells are really crappy. So we want to be free to do what we want on machine-made cells. We've established some links with Chinese battery makers who make pouch type lithium-ion cells that we buy dry without electrolyte in. Those come to us in lots of 2000.
The minimum I can buy is 2000 which is actually a pretty good number. We bought a vacuum sealer so we can seal these pouch cells at Dalhousie with whatever electrolyte we want. So this is a big step for us, and it's good, really good.
I want to tell you what we're doing with these things in one experiment. That is any these parasitic reactions in a lithium-ion cell should make heat and if you use a very sensitive microcalorimeter - you should be able to see the heat.
So in our automotive partnership project we bought this microcalorimeter from TA Instruments. It's an amazing device - it has 12 calorimeter ports, so you can test 12 cells at once. We wired each of the ports so we can charge and discharge cells down in the calorimeter. So an isothermal calorimeter, all experiments were done at 40 degrees C, and it measures the heat that the battery is outputting or the heat that's flowing into the battery.
The machine works like a total charm, and it can hold these pouch cells that I'm talking about. The sensitivity is 10 nanowatts and the baseline stability is better than 500 nW over a month.
I'll tell you in a minute and show you the data on how much heat these pouch cells produce due to the parasitic reactions.
The heat that's given of an experiment like this - there's three sources.
When the lithium content in the electrodes changes, the entropy of the electrode materials change and there's a heat flow associated with those entropy changes - we're not interested in that.
Every battery has internal resistance or polarization between charge and discharge and there is a heat flow from that - were not interested in that either
The parasitic reactions due to the electrode electrolyte reactions - that's what we want to measure.
We have to be able to separate this from these other things that we don't want to measure. Now what sort of scale of heat flow are we looking about here?
So the cells store a watt hour of energy, they are 200 milliamp hours at four volts, so roughly a watt hour. The energy inside the complete electrolyte electrode reaction turns out is also about a watt-hour - that’s a rule of thumb for lithium-ion cells. The electrical energy is equal to the chemical energy that would take place if the electrodes reacted with the electrolyte.
If parasitic reactions occur at a rate that would consume all the electrolyte in a year, you would get a 100 microwatts. So 100 microwatts is bad. If you see 100 microwatts of parasitic reaction, that's very bad. Very, very bad.
Here's some experiments. So these are identical pouch cells, lithium cobalt oxide graphite pouch cells. One has control electrolyte and the others have different amounts a vinylene carbonate in them. They were the first charged and discharged in one open circuit. Then we discharge them, charge them, discharge, and charge them.
We did a very slow charge and discharge and I want to just concentrate on this range.
If you look very carefully up here, you'll notice on the heat scale, there's all kinds of stuff happening. Entropy changes, polarization, and so on, but the cells are identical so the entropy changes should be the same in all them.
The internal resistances are basically the same.
So the only difference between the heat output in these cells here is due to the parasitic reactions, and the heat from the blue and black is less than the red. So this is a crappy graph, right? That's what you would put on your screen just to see what happens. When you look at this you say when I really want to do is plot the heat flow versus the voltage. If you do that, what would you get?
I've added a data set for half-percent VC now as well.
At low voltage, 3.9 volts, all the four cells are about the same. Then there's a big entropy change due to an order-disorder transition in lithium cobalt oxide. But after that, between 4.1 and 4.2 volts - look - here's no vinylene carbonate, 0.05%, less heat, 2 and 4 percent, less heat again. And the difference gets greater with voltage.
So the vinylene carbonate is suppressing parasitic heat due to electrolyte oxidation. We saw that early on from our charge slippage measurements. You can see that at voltages above 4.1 volts or so, the impact of vinylene carbonate starts to get very important.
Look at the scale. So this is from that tick mark to that is 200 microwatts. So it's suppressing things by a border of 100 microwatts. That's important. So in a single experiment, you can learn about the voltage-dependence of the impact on the electrolyte additive or blend of electrolyte additives.
On just a single experiment. I don’t know how you can do this any other way but it all relies on having access to identical cells to do a measurement like this.
Pretty cool.
Alright, so, I’m done. I'll just make a few remarks:
High-precision coulometry and other methods like calorimetry will speed the development of advanced lithium-ion battery with longer lifetimes.
3M has been a partner with us for a long time but we have more partners now and everybody sees the value of these methods and the rest the world is catching on and moving into this area too.
But really the main part of the product is answering the questions:
This is by far the hardest problem I've ever worked on in my life. It will take the rest of my career to maybe make some answers to this and I don't even know if we will.
We've got a couple techniques like this high precision coulometry and microcalorimetry and storage and impedance with surface science measurements. XPS and FTIR and other things that people want to do to learn how these additives work. This is where my group is going now, is to answer the why questions.
We built the characterization tools from an electrochemical point of view and now it’s time to do the hard stuff.
Thank you.
[Minute 58:00]
Question 1
Now when you were predicting the failure of your batteries, it takes a model where, the failure, the gas, [unintelligible] negative electrode, right? But you have data to show the batteries from the manufacturer, they are not far from the prediction, which is using that model. So do you think there are alternatives, maybe, beyond what you do in terms of a model?
Question 1: Response
This is about the simplest model you can ever come up with. I thought of that walking home one day.I wasn't writing fancy equations on the blackboard for years. I'm a simple minded guy and I like simple stuff. So when you do science, it’s good to work with a working model in mind and you say, well maybe the data is gonna fit this. And if it doesn't then you have to say “this is insufficient, right?” So you have to go beyond that.
Definitely you gotta go beyond that, right?
Question 1 Follow-up
So have you got any advancement… or?
Response:
Well I will show you one thing. I skipped over this in the lecture. So these guys here, imagine that this one is not making solid reaction products on the negative. 3UE, okay? So what would the impedance of that cell be like compared to these guys. Well there's no film of solids, the impedance should be lower.
So we measured the impedance of all these cells before we sent them back to the manufacturer for the long-term cycling.
I’ll show you the impedance of 3UE compared to everything else.
These are impedance spectrum (I don’t know if you’re familiar with this) but the thing that's important is the width of the semicircle here.
Look at 3UE! It’s the smallest by far of everything. If you look at the difference between 5UA which is here, and 4UA which is here. 5UA has a lot less impedance than 4UA, and then you go back to the previous thing [he is referring to the previous graph], and here's 4UA and 5UA is building less solid products on the surface, you know, and less impedance - there it is.
So if you make a 3D graph that includes the effect of impedance here… here's one minus one over C. If you go that way things should get better. Here's impedance, and if you go that way things should get better, and all the points fall on sort of a surface except that guy, and there is one outlier.
So I think the missing ingredient here is the surface film on the negative. Are you making a solid surface film or not? If you are not, that's what you want. You want that kind of an additive. You want to limit the amount of electrolyte oxidation, but you also want to make those solid products.
Long answer to a question.
Question 2: [Video skips question]
Question 2: Response
We haven't done any work, with these methods, with silicon in any great degree. But you're right - different additives are beneficial for silicon, for sure, than graphite. No I don't think you need to bring the power of these methods to silicon at this point. Silicon shows so much SEI growth on every cycle because of the volume change, that you can see the parasitic reactions with a traditional charger.
If you just have a lithium silicon cell going, and you measure coulombic efficiency - it'll be 98 percent or 96 percent or whatever it is, unless you’re cycling really fast.
You need these fancy chargers for silicon-based electrodes yet.
[Unintelligible follow-up question]
Silicon is light years away from having lifetimes like these cells i'm talking about. Silicon is light years away, okay? Maybe in ten years it'll be a thousand cycles and last a few years but it's light years from there now.
Question 2: Follow-up
If you used this to look at something like lithium titanium oxide, which has a much higher potential, you can see where the electrolyte actually forms, actually where the electrolyte oxidized product ends up being reduced - and at what potential does that plus get reduced?
Question 2: Response
Lithium titanate is amazing. It's because the voltage is high. I don’t have a lithium titanate slide here.
Sort of the best coulombic efficiency numbers we get for C over 20 cycling at 40 degrees C for graphite negatives and lithium-ion cells is about 9992. Lithium titanate with lithium-ion cells we would get 99998. Amazing. Lithium cobalt oxide lithium titanate cells with a 4.1 volts... amazing.
They’re going to last till she's dead. [Laughing] No doubt - even in you they’ll last till you’re dead. Even though you have a big advantage in years.
Question 3
Is there a way to relate the lifetimes in CHBC [audio not clear] measurements to something like a drive cycle? Can GM say that because this cell in an HBC measurement is 10,000 cycles that relates to 10 years?
Question 3: Response
This is what's gonna happen. So we're working with GM now. It's an experience for me because GM doesn't make lithium-ion cells - they buy them. So they haven't thought about what all this stuff means too much and they want to do what you’re saying. Say “the high percent charge says this, and all of a sudden the drive cycle says that.” So what I tell them is “this what you gotta know, what is a lifetime of your current technology and the test you currently run?”
Then we do the measurements on your current technology and whatever's coming next. And we compare, and we can tell you what's coming next is gonna be worse or better and make a projection about how much better.
But for me to go from high-precision cycling data without any other knowledge to predicting what a drive cycle is gonna do... impossible. So GM is sort of coming around now and coming to see.
You can also do things like see what's the impact of the lifetime of the drive cycle - you look at how the coulombic efficiency varies with temperature, and then you can get arrhenius laws and whatever and go back to the drive cycles that way.
So I don't really know how to answer your question well today... probably in a year or two these kind of things will have developed somewhat.
Question 4
Just a quick question. For the purposes of lifecycle testing and determining the buildup on the electrode in these things, are all cycles create equal? So it seems that when they do this battery testing, they use a constant charge rate and a constant discharge rate. But if you’re looking at an EV for example, you drive to work, it holds at a constant charge, then you drive it a little more, it’s at a grocery store so you can [unintelligible] a little more.
So your charging is not a linear constant discharge rate, right? And it is discharging sporadically throughout the day. I don’t know if this affects anything though. But it was sort of related to his last question - they’re doing constant charging and might have overnight charging. But if they’re testing it at constant charge and discharge rates, this might not be indicative of drive cycles at all. I don’t know if this affects anything.
Question 4: Response
The biggest issue is the time spent at highest voltage. The longer you spend at the highest voltage the worse it is. You could see from the calorimeter experiment things got worse when you went up above 4.1 volts. So if you go to 4.2, it’s worse than 4.1. If you go to 4.1 it's worse than 4.0. So the GM Volt for example, it charges to 80 percent which is 4.03 for that cell, which is decent. Not too much parasitic reactions going on there. But if it charged to 100 percent, it would be worse. So all cycles are not created equal to answer your question.
The more time you spend at higher voltage, the worse.
I have cells from 1999 that were stored at about 20 percent state of charge so maybe 3.5 volts for those cells. We put them on in 2013… and they are like new. Because the positive electrode side is not doing anything bad at low voltage.
But if they have been stored at high voltage it wouldn't have been nearly as good.
Question 4: Follow-up
This might be a consumer education thing - don't keep your EV topped off at all times.
Question 4: Follow-up Response
Well the the battery manufacturer's way around that is going to be to select technology that is OK at the voltage it's going to. So it's it's gonna be under control. People will sort of understand this.
Question 5: [unintelligible]
Question 5: Response
There are no redox holes in in any of the cells. There are no intentionally added redox shuttles in any of the cells, let’s put it that way. Maybe some molecule gets created in some funny way that lowers the coulombic efficiency a little bit... some shuttle action.
Question 6: [no audio available]
Question 6: Response
No I would say interest is not waning at all. All the automakers have various things underway.
Mercedes has the EVs and Diesels and all that stuff going on at the same time. BMW has a big EV project, and I think the diesel guys are excited, the gas guys are excited, and the EV guys are excited. Everybody's excited, and I'm excited!
Question 7
Can we turn to page 22? [Rest of question audio not intelligible]
First it goes slightly to the left, and then it starts going to the right. It goes left first and then to the right.
It's a pretty tiny leftward shift and a pretty tiny rightward shift.
Do you know about overhang? Overhang in lithium-ion cells? The negative electrode is slightly wider than the positive. That's because if the positive electrode were opposite nothing, and you recharge the cell, the lithium would come out and electroplate on edge of the negative and form lithium metal dendrites. So the negative electrode is wider.
That means there's extra graphite out on the overhang so some of the lithium from the positive goes over there and you often get weird things happening at the very beginning of cycling when this overhang equilibrates with the amount of lithium in it. It’s very technical, but when you look at the fine scale like you're looking - things get technical.
Question 8: [no audio available]
Question 8: Response
A combination of both, absolutely. There's a lot of folks that are in the battery companies that just test stuff. What we've been starting to do, which is just a slightly higher level is, we’re trying to see which additives are working, and say there's a core on that like a sulfur double bonded to oxygen, or a sulfur double bonded to two oxygens. And then the rest of the molecule you can change in a systematic way and see what happens.
There are people there doing theory. We need more people doing theory.
Question 9: [unintelligible]
Question 9: Response
Keep it as cool as possible at all times. Put it in the fridge at night, then it won't bother you while you're sleeping too. [laughter]
Added advantage. No but I'm serious - if you keep any battery as cold as possible it will last longer. So any lithium ion cell, you should keep in the fridge when you're not using it, it will last longer.
If you don't charge to a hundred percent that will help. But you know temperature is a bad actor - keep in the fridge. If you don't mind condensation on the keyboard when taken out.
Question 10: [unintelligible]
Question 10: Response
That stuff is not what I would call SEI. This is the the reduced oxidation products coming from the other side - it's junk. That stuff you can see it with an SEM. The normal SEI, what you would call SEI, is you know, just a few nanometers thick. You can’t see it on an SEM at this scale. This junk that has come from the positive and been reduced on the negative surface.
]]>Here is a picture of their rover with a functional robotic arm attached.
Battery Bro recently provided 18650 batteries to the Mars Rover Design Team at Missouri S&T.
We are fascinated by space, and the see lithium-ion as an "enabling technology" that can help us reach the world's spacefaring goals.
As such, we asked the design team for an interview which they were happy to oblige!
We spoke with Alyssa who answered all of the questions below on behalf of her team.
Chief Executive Officer
1. What is the purpose of your project?
The Mars Rover Design Team is a student run design team located at the Missouri University of Science and Technology (Missouri S&T) in Rolla, MO. The purpose of the competition is to design & build the “next generation” of Mars Rovers, that will one day work alongside humans in the field. The team competes every year in the University Rover Challenge (URC), an international competition held in Hanksville, Utah. The team has been competing for three years. In 2015, we also became the first American team to ever compete in the European Rover Challenge, held in Kielce, Poland. The team placed 10th out of 44 teams from all around the world! Find out more here:
marsrover.mst.edu | urc.marssociety.org
2. Why did you choose LG INR18650HE2 lithium-ion cells for your project?
We chose these cells due to their high current output and excellent value
The custom lithium-ion pack configuration used in the rover
3. What kind of pack configuration do you use for your cells, and why?
We have the cells configured in eight modules in series, with each module housing 10 cells in parallel. We use this configuration to achieve our desired output of 33.6 volts at a maximum of 200 amps.
4. What kind of temperature extremes will the rover experience, and how will you control for them?
While the rover will not actually go to space, the deserts of Utah can have some pretty extreme heat. We are planning on implementing a cooling system with fans to prevent the batteries from overheating, and will be closely monitoring the temperature of the batteries between tasks.
5. Are there any other dangers to your battery system posed by the extreme environment in space?
Should the rover actually go to space, there would have to be some radiation-protection casing covering the cells, protecting both the cells and the rover from any extreme environments it may experience. In order to save cost, the competition does not require us to design for the actual atmosphere of Mars.
6. How do you regulate the battery output (e.g. BMS), and how does that have to be adjusted for space?
The battery output is regulated through our custom battery management system, which monitors the voltage of each module as well as the current output from the pack. The output is regulated further at our custom power board, which steps the pack’s voltage down and again monitors voltage and current outputs. Whenever these outputs behave unexpectedly, these systems are programmed to turn off voltage busses or disconnect the pack entirely from the rover. Again, the competition does not require us to design for space conditions, saving us both time and money.
The battery array will be a long, flat surface that will slide underneath the rover, instead of the cube-like array from last year. Leaner & lighter is one of the main themes this year.
7. Are there any unique or unusual aspects of your pack design (form factor, tabbing, etc.)?
To connect the individual cells in parallel to form our modules, tabbing is spot-welded across the cells’ terminals. To connect these modules together in series, custom 3D-printed moldings are used and screwed together. In addition, the batteries are laid in a pallet-like configuration, similar to the way Telsa battery cells are laid out. This lowers the center of gravity, and also allows for physical separation between battery terminals. Similar to Teslas, this configuration requires us to design and build a skid plate for the bottom of the rover.
8. What is the planned recharge / use schedule for the batteries?
a. Do they shut down during the Mars night?
b. If they recharge during the Mars day, how long does a full charge take?
This year, the BMS also charges our batteries, so we will not need an external charger. They will be charged between competition tasks and also at night. A 90% charge should take about 2-3 hours, plus varying time for trickle charging.
Learn more
If you are interested in learning more about space batteries, a .PDF published by NASA titled Guidelines for Lithium-ion Battery Use in Space Applications (54 pages) is the ideal place to start.
Current space batteries
Curiosity, Spirit, and Opportunity all use lithium-ion batteries created by Yardney.
Yardney batteries boast the following characteristics:
Future
As you can see, a key differentiator is the temperature which the cells can handle. Typical 18650 batteries are not able to perform under 20 degrees Celsius. This is a good target for cell innovation.
One such battery chemistry uses internal resistance to create self-heating cells (Link: Nature) which would save energy (lessen cell degradation and facilitate less environmental heating).
What other innovations are needed for batteries to work well in space?
Thank you Alyssa McCarthy for talking to us about your rover batteries.
]]>
A jumbo jet with its nose cargo door open. It sure would be a nice place to put some... batteries...
Electric airplanes are perhaps the most exciting prospect for the future of aviation.
The record-breaking Solar Impulse II is one of the projects that shows how much things can improve. In a previous article, we covered the tech involved to get the Solar Impulse II airborne.
Last year, the plane was grounded in Hawaii because of batteries overheating. After completing a five-day long, 7,212km journey across the Pacific, the Solar Impulse 2 showed us the feasibility and the opportunities that lithium-ion batteries can bring to the aviation industry.
The decisions required to make those advances are being discussed as we speak.
With rules as they are now, it’s nearly impossible to add technological improvements that modify the mechanics that have kept airplanes working since the 1960’s. This applies for almost every kind of airplane you can imagine, except those that are considered to be used as a hobby. That is, carrying 1 or 2 passengers. This turns out to be frustrating as there is great interest in offering more efficient designs that can reduce oil consumption during flights and reduce the environment footprint that today’s airplanes leave behind.
Yes, the proposal only applies for small airplanes, but the changes that could be done are of such a magnitude that they could open the doors for the whole industry. To get there, it'll take a long time because the improvements made have to be thoroughly tested for them to be safe, because that's the FAA’s highest concern right now.
To give an example, in 2013 Boeing introduced the 787 Dreamliner, an airplane that would add additional electrical systems, complying with the FAA’s requirements, in order to reduce fuel usage and be more eco-friendly. They used certain Li-ion battery from a manufacturer called Yuasa, and because it didn't have a proper short circuit protection built-in, it had a failure within the first few months of operation after its introduction, burning the circuit that goes over the battery in the process.
Here’s the comparison between a brand-new battery and the remains of the one involved in the incident.
This event caused a lot of concerns in specialized media, leading Yuasa to retire said battery from their website’s product listing. Boeing acted quickly and made the necessary modifications to their systems and no new reports of incidents regarding their electrical systems have come up to date.
This kind of circumstance is a headache because companies can’t use their full potential to provide more efficient designs to larger airplanes - a situation that this proposal can change if it provides results relevant enough for the idea to gain traction. An age of sustainable innovation in aviation with fewer roadblocks.
Considering the time it could take for such a change to happen in the industry, let's take a look at the feasibility of using electric batteries that are already in our homes and what’s available in the market. Let’s see how many we would need to satisfy the energy requirements of putting a commercial airplane in the skies and maintaining its energy consumption during a normal flight.
We'll take a broad approach to the calculations, to keep them simple and manageable. We’re not aviation experts nor are we considering the weight of the systems involved to keep the batteries connected and safe for travel. Just raw energy density.
For weight considerations, we used the weight capacity that the airplane has for fuel in kilograms.
As test subjects, we will be using three widely-used large airplanes that many of has have flown on:
Boeing 747-8F
Boeing 747-8l
Airbus A320
The specifications of each airplane took into consideration for the calculations will be shown in a table, for practical reasons.
As there’s such a wide variety of batteries in all types and sizes from each manufacturer, we’ll take two batteries that everyone knows - Blackberry and Samsung smart phone batteries.
Let’s also take two leading-edge batteries developed for more power-consuming applications, the Yuasa battery discussed earlier, and the Tesla Powerwall.
A typical mobile phone battery
A powerwall next to people for scale, image credit: Gizmodo Australia
Specifications used for calculations are shown in the table below, and the considerations that are taken for each case.
For each type of battery, we’ll determine:
If we compare the amount of batteries we can carry compared to the amount needed to feed the enormous energy consumption rates that commercial airplanes have, we can see that there's a lot of work to do.
Looking at the data, we'll see that:
The Blackberry D-X1 battery doesn’t look very good for these results, but that’s expected considering that fuel’s energy density surpasses greatly the one available to be used from the batteries by the airplane.
A custom lithium-ion pack would be an alternative to getting more energy density, providing at least three times the amount of energy these batteries provide with an improved configuration.
The energy stored rate for these batteries is the lowest of the batteries tested, but that’s likely due to:
At last, but not least, we have a Tesla Powerwall. If you don’t know what it is, it’s a big box full of lithium-ion 18650 batteries that can power your house (optimally in conjunction with solar panels).
What would happen if you stuffed jumbo-jet fuel tanks full of Tesla Powerwalls?
In this case, we can see that:
Compared to previous batteries, this battery is just below the Galaxy S4 battery in terms of stored energy. However, these batteries bring with them the idea of being constantly recharged via solar panels. If we manage to also borrow a few of the ideas used in the Solar Impulse II we could be looking towards a self-sustained airplane, at least for its in-flight energy consumption needs, as the batteries have more time to recharge themselves during flight.
After giving a look at the strengths and weaknesses of various battery systems we can come to the conclusion that there’s a long way to go in order to improve both energy density and weight of batteries if we wanted to use them as the airplane’s only energy source, but we can see there’s a lot of motivation and interest to bring the technological improvements needed to do so as soon as possible. With innovating designs regarding engines, batteries, and even aircraft designs, the approval of Rule 23 modifications proposal could be a golden opportunity to show off the improvements that alternative energy sources can provide to the aviation industry, and the much-desired pollution reduction in order to have a more sustainable future.
This NASA jumbo-jet breaks expectations and shows us that the future of aviation can be interesting.
Some possible further questions to ask:
What other advantages do lithium-ion powered planes have over traditional engines? Could they perhaps go faster than traditional planes without a loss in efficiency?
Note: if somebody wanted to improve the calculations made, it would be a good idea to calculate the amount of energy needed to keep the batteries at an optimal temperature, efficiency between charges, and the weight of the equipment needed to build a large, safe custom battery pack.]]>
In this short 2-minute video, MIT explores how lithium-ion 18650 batteries are produced.
These particular batteries are different because their electrolyte is stable up to 300 degrees Celcius. Whereas traditionally, the 18650 batteries we sell on Battery Bro for example only keep a stable electrolyte up to 70 - 80 degrees Celcius.
The steps to create the batteries are as follows:
Finally, the cells undergo charge and discharge testing at various temperatures.
*Did you know? The word hermetic comes from the Greek God... you guessed it, Hermes! That is because Hermes inspired alchemy. A hermetic seal just means it is air-tight.
---
Want to watch more? Take a look at this slightly longer 7-minute video for a broader overview, from mining to use.
]]>Cells deconstructed from the top, Panasonic A, Panasonic B, Sanyo FM showing various lengths of electrolyte foils.
This blog article will explore the differences between a sampling of Panasonic, Sanyo, and Ultrafire 18650 batteries.
To do so I will exclusively refer to a paper published here in 2015.
Background
Lithium-ion was first made available in 1991. Since then it has become more apparent that it is the best solution for energy storage. However one problem with lithium-ion and the 18650 battery is the difficulty in getting reliable, honest ratings.
It’s hard to know whether the specifications are true because:
Cells tested
The cells tested from left to right are:
The most important physical characteristics that distinguish the 18650 are:
The 18650 (18mm by 65mm) has evolved as the best trade-off between capacity and charge/discharge ability in terms of these characteristics.
Other 18650 battery characteristics
There are many conditions that will alter the performance of your cells.
The max and min voltage can be reduced from the extremes.
For example instead of charging a battery to 4.2 V and discharging to 2.5 V, one might only use a range between 3.2 V and 3.8 V. This can lead to an increased cell cycle life.
The capacity at the beginning will be greater than any proceeding time because of natural cell degradation.
An increase in charge or discharge amperage will decrease the working capacity and life cycle of a cell.
Furthermore, any deviation from the testing temperature of 25 degrees Celcius the cells will result in reduced performance. This is especially true under 0 degrees and above 60.
Other testing variables that should be accounted for when accurately testing cells:
Initial results
P 3100 | P 3400 | S 2600 | UF 4200 | UF 4900 | |
Typ. Charge Capacity (mAh) | 3070 | 3350 | 2600 | 4200 | 4900 |
Min. Charge Capacity (mAh) | 2950 | 3250 | 2500 | - | - |
Meas. Charge Capacityb (mAh) | 2862 (2961) | 3166 (3267) | 2480 | 757.1 | 579.4 |
– (% of typical) | 93.2 (96.4) | 94.5 (97.5) | 95.4 | 18 | 11.8 |
Meas. Energy Capacity (Wh) | 10.19 (10.61) | 11.33 (11.78) | 9.25 | 2.74 | 1.96 |
Nominal Weight (g) | ≤47.5 | ≤48.5 | ≤48 | - | - |
Measured Weight (g) | 44.66 | 46.7 | 45.62 | 32.24 | 37.98 |
Nominal Length (mm) | ≤65.3 | ≤65.3 | 64.9±0.2 | - | - |
Measured Lengthd (mm) | 65.08 | 67.34 | 64.96 | 65.74 | 65.44 |
Nominal Diameter (mm) | ≤18.5 | ≤18.5 | 18.3±0.2 | - | - |
Measured Diametere (mm) | 18.28 | 18.57 | 18.28 | 18.27 | 18.22 |
Specific Energy (Wh/kg) | 228.3 (237.6) | 242.6 (252.3) | 202.8 | 84.8 | 51.6 |
Energy Density (Wh/l) | 596.9 (621.3) | 621.3 (646.2) | 542.6 | 158.7 | 114.8 |
Cost per Cell (AU$) | 11.48 | 13.48 | 5.31 | 1.45 | 1.63 |
Cost/Meas. Capacity ($/kWh) | 1125.9 (1081.8) | 1189.7 (1144.0) | 574.1 | 530.1 | 831.7 |
Cost/Meas. SE ($kg/kWh) | 50.29 | 55.56 | 26.19 | 17.09 | 31.59 |
Step 1: Charge and discharge
Charge to 4.2 V at 1A and then taper charge to 50 mAh and terminate.
Then,
Discharge at 1A
Stage 2: Weight and dimensions
Taking measurement of weights especially enable comparisons of 18650 battery energy density. Weight is a critical constraint in electric vehicles especially as it reduces the km driven per charge.
Stage 3: Impedance
Checking the impedance - cells tested at a frequency range of .1 Hz and 100 kHz.
Step 4: Aging and life cycle of cells.
Testing to conclude after 100 cycles, or by the end of the month whichever happened first - how much the capacity has faded and impedance has changed.
Step 5: Rest and test
Let the cells rest for anywhere between a couple days to a few weeks. And then take a final capacity test in the same conditions as the very first test. That will show how much the cell degraded between first and last test.
Dimensions
All 18650 cells are actually slightly larger than 18mm by 65mm. The paper found the diameter is 3.2% and the length is 3.6% larger than the 18650 standard. It’s important for those who want to create large battery packs with thousands of cells.
Interestingly, it also skews the “lithium-ion energy density measurements” that everyone uses as the size is a critical component of the formula and seldom is it accounted for.
Capacity
Battery | mAh | Cycle | Av. Capacity Reduction per 100 Wh Throughout (%) |
Panasonic | 3100 | partial | 0.43 |
Panasonic | 3100 | full | 0.7 |
Panasonic | 3400 | partial | 0.57 |
Panasonic | 3400 | full | 1.51 |
Sanyo | 2600 | partial | 0.75 |
Sanyo | 2600 | full | 0.66 |
Ultrafire | UF4200 | partial | 3.71 |
Ultrafire | UF4200 | full | 2.24 |
Ultrafire | UF4900 | partial | 16.6 |
Ultrafire | UF4900 | full | 67.9 |
Panasonic cells achieved over 93% of their advertised rated charge capacity. The Panasonic cells did not reach their full capacity because they did not use the proper cut-off voltage (2.5V) and they used a “fast” charge current of 1A where they might use .5A or lower. Furthermore optimizing the temperature would have likely allowed them to reach their full potential.
Ultrafire cells were between 12% and 18% worse. There is no surprise here.
Full Cycle Life
There is clear downwards aging trend after 50 - 130 cycles
Partial Cycle Depth of discharge study
Charge and discharge from 3.2 to 4.0 V, to decrease the depth of discharge. This should offer an increase in the cycle life of the cells.
Note, the Depth of discharge, or (DOD) differs from the state of charge (SoC) by being an alternate way of measuring charge, albeit somewhat reversely. When one goes up, the other goes down.
The comparison between cells fully cycled and cells partially cycled is interesting because it can help you decide between two options:
If we look at the chart we can see that the Panasonic cells to degrade slower when having a decreased voltage range. Unfortunately, the Ultrafire cells do something not expected for 18650 batteries - they degrade much faster.
Unfortunately, this makes the data (because of the cells) unreliable - calling for more cells to be tested for conclusive comparisons.
However if you just focus on the Panasonic and Sanyo cells you can see by limiting the depth of discharge there is some improvement in the life cycle.
Panasonic Cells
What is charge transfer?
Now most readers have no idea what charge transfer capacitance is, but if you are curious you want to know. It begins with something called the charge transfer coefficient.
In lithium-ion cells, charge transfer is defined as the fraction of over-potential that affects current density.
Overpotential is a measure that directly translates to voltage efficiency (using more or less energy than thermodynamics require). Inefficiencies are seen as a loss of usable energy in the form of heat.
Sanyo Cells
The same thing happened to these cells (charge transfer capacitance decrease, diffusion increase).
The difference between the Sanyo and the Panasonic cells are an increase in ohmic resistance (how much is the cell opposing the flow of current). This is due to the battery chemistry type, notably the electrolyte formulation which is outdated.
Ultrafire Cells
The same trend continues here.
The big difference is the Ultrafire cells had a much higher increase in ohmic resistance. This could have been predicted - these cells are terrible.
Initial capacity testing found the Panasonic and Sanyo cells performed within 8% of their rated capacity.
Panasonic and Sanyo cells:
Ultrafire:
More on the Ultrafire cells
The authors of the paper found that actually inside many Ultrafire batteries are smaller batteries. It’s not Russian dolls, it’s cheap 18650 batteries!
Counterfeiters purchase blank 18650 steel tubes and then don’t fill them up all the way. It’s the classic potato chip bag bait-and-switch.
The electrolyte foils were found to only comprise 73% to 74% of the space the Panasonic or Sanyo cells did.
CT scan of Ultrafire batteries.
Last picture - the Ultrafire 4200 from this article cut in half.
Source:
Vyroubal, P., et al. "3D Modelling and Study of Electrochemical Characteristics and Thermal Stability of Commercial Accumulator by Simulation Methods." Int. J. Electrochem. Sci 11 (2016): 1938-1950.
]]>"Effect of variable power levels on the yield of total aerosol mass and formation of aldehydes in e-cigarette aerosols", March 2016, link
But since its a scientific publication, it is not very readable or quick to skim through.
So let's break it down into ELI5 language (explain like I'm 5). That way anyone can quickly, in a couple minutes, gain critical knowledge to make better decisions about their health.
Please note: Battery Bro is not making any opinions or advising on any health decisions you might make. We are simply looking at one recent paper and breaking it down.
Chemicals involved in vaping
E-cigarettes (EC) work by heating a coil which is attached by a wick to a tank. The tank contains:
Propylene glycol (PG) is the most common liquid for ECs that is aerosolized when inhaled. Aerosolization is the process when some particles are made small and light enough so that they can travel through air (and in this case into the mouth and lungs).
The problem occurs during the heating of mixtures of glycerol (GLY) and propylene glycol (PG). During this complex process, something called Aldehydes are known to form. Aldehydes are a relatively common organic compound - that is a member of a large class of things which contain carbon.
Aldehydes that are claimed to form during the heating of PG and GLY are formaldehyde, acetaldehyde, and acrolein.
The paper this blog post is about, is trying to determine how watts (power) might play a role in the production of dangerous chemicals. Some questions you might ask yourself:
So far, studies have come out in two fields.
Group A has studied low power, prefilled disposable devices - often called version one e-cigarettes. These smaller devices look like a cigarette and don’t use 18650 batteries. In these studies, the aldehydes produces are much lower in comparison to tobacco cigarette smoke.
Group B has suggested that newer vaporizers, mainly those with refillable tanks and using higher power 18650 or lipo batteries may actually produce more aldehydes than tobacco cigarette smoke.
So that’s the problem, that this paper attempts to address. Who is right? And how much does wattage actually affect the production of dangerous chemicals?
Devices
Five devices were used I’m sure many readers are familiar with:
Liquid
The liquid used for all tests is: 48% (wt/wt) propylene glycol (PG), and glycerin (GLY), with 2% nicotine. Liquid was never allowed to be less than half-full in the tank.
Power
The battery for devices 1, 2, 3, and 4 used was the Innokin iTaste VV4 battery. Voltages were tested at 3.8, 4.2, 4.7, and 5.0V. Device 5 used a DNA 40 at 10, 15, 20, and 25 Watts.
Mass
They calculated the total mass of the “cloud” or aerosol per each puff. Each puff lasted 4 seconds, with a wait of 30 seconds in between. By adding more power they were able to make clouds ranging from 1.5 to 28 mg.
To give you some perspective, a paperclip is 1g, so the maximum mass of the aerosols produced could be thought of as 30/1000th of a paperclip’s weight. A box of 25 puffs weighs between 38 mg to over 692 mg.
What they found
By purely comparing mass, three vaporizers were found to produce more aldehyde when more power was given to the coil. But two of the vaporizers actually had a decrease in aldehydes with increased power
The range of bad chemicals produced across all of the devices tested:
Calculating daily exposure for vapers
They averaged the amount of vape juice or e-cigarette liquid across both normal and experienced users, and found that on average, 3mL is consumed every day.
3mL of daily vape juice is approximately 3g. Multiplying the above range of figures for 3g yields the following daily range of possible aldehyde consumption:
In comparison to what is found in one pack of tobacco cigarettes:
We have made some charts with the data:
As you can see, the upper range when vaporizers are working poorly they are competing with cigarettes for toxins released.
However on the lower range of the data, you can't even see the effects of vaporizers compared to cigarettes. (You can hold your mouse over the bar to see the data for vapes).
Results the paper finds
All devices performed very differently!
Overheating the atomizer because of insufficient liquid may be the cause of aldehyde production
The purpose of the paper is not to say tobacco is better, or vapes are better
Device 1 - Very bad
[Important note! This device was found to have a charred coil, indicating that “dry puffs” and damaged coils should be replaced immediately as they may cause increased aldehyde yield.]
Device 2 - Needs work
Device 3, 4, 5 - Good
Device 5 - Excellent
We have taken the creative commons data from the paper and made some charts so you can more easily see what is going on.
The intention is to see if wattage does increase the amount of aldehydes produces in each device so note the direction of the trend lines.
The data is comparing a vapers aldehyde consumption per day to the amount of power (watts) applied from the battery.
Problems with this paper
The interesting effects of wattage on e-liquid are just beginning to be understood. No one really knows what is going on, and the researchers who published this paper will most likely be the first to admit that.
The paper does indicate that dry-puffs (not enough liquid on the coil) may be causing the production of chemicals like formaldehyde.
More power and higher watts may not directly make e-liquid more dangerous. However higher watts, without liquid to be efficiently aerosolized may produce more dangerous chemicals.
Thanks for reading, if you have any questions or comments please post them below.
]]>General on shipping lithium ion batteries:
http://www.iata.org/whatwedo/cargo/dgr/Pages/lithium-batteries.aspx
Specific to the April 1st update:
http://www.iata.org/whatwedo/cargo/dgr/Documents/lithium-battery-update.pdf
---
Bulk shipments of lithium-ion batteries will be banned from passenger plane cargo holds. The recommendation will start being implemented on April 1st 2016. It is mandatory for 36 airlines which are members of the International Civil Aviation Organization, but is not compulsory for everyone else.
To be clear, this ruling does not have anything to do with carrying lithium-ion batteries onboard a plane, in your pocket or your laptop bag. ICAO’s ruling on the personal transport of small lithium battery powered devices (including hoverboards) is here:
http://www.icao.int/safety/DangerousGoods/Documents/eb001e.pdf
To summarize the bulletin:
But again, that is about personal use, not about bulk shipments. ICAO has released a clarification stressing this point here:
To summarize:
This new ban on lithium-ion batteries as cargo is temporary. The ruling is only expected to be enforced until 2018. Why are they expecting 2018, and not setting an actual date? The problem, always, comes back to safety.
In the current situation there is no safe, viable way to put bulk shipments of li-ion batteries onboard planes (passenger, or cargo). Well there are, but they are far from affordable (think, heavy fireproof cases and gases needed to moderate the atmospheric pressure). Even as scientists try to predict that they will have a solution by 2018, it is likely the date is arbitrary.
It may be that a solution will be reached much sooner because of push-back. Or maybe it will be reached much later because of fundamental physical constraints.
This is what a cargo hold on a 747 passenger plane looks like. Note the interesting sign at the back stating "Do not hit - portable water tank inside".
There is a lot of friction and the decision was not an easy one. New markets for electric vehicles and other lithium-powered devices are really driving demand for batteries from Asia. Reducing the efficiency of transport for the integral commodity hurts growth in high-tech sectors and has wide-reaching implications.
One of those is medical devices. The Rechargeable Battery Association has argued that transport restriction and logistics issues will reduce access to lithium-ion battery packs in developing countries. While this may be true, it is also likely that smaller carriers in developing countries will opt out of the unforced ban.
Luckily, bulk shipments of li-ion batteries are still allowed aboard cargo planes - those designed specifically for dangerous goods that do not carry any passengers. There have been several deadly cargo plane crashes over the last decade because of li-ion thermal runaway events, but grimly they are an understood workplace hazard.
I personally welcome the UN ruling with open arms. Lithium ion batteries pose a danger to both crew and passenger safety and removing bulk-shipments from passenger planes really is a no-brainer. Imagine travelling in an airplane, with TNT onboard… and that is precisely the danger we are talking about.
A thermal runaway event is when one battery catches on fire, setting off a chain reaction. The combined heat starts triggering fires and explosions in adjacent cells and so on. Bulk shipments may contain 10,000 cells or more.
While the danger of passenger plane thermal runaway events has been mitigated, there are still two grey areas which pose risk:
So far they have not been discussed in detail by the aviation board. Possible scenarios are tougher enforcement and higher fines for undeclared battery shipments and counterfeits - but there would have to be large-scale cooperation with China where most of the fake batteries come from.
Interestingly enough, China was one of the countries in favour of the ban in a panel vote in 2015. The other countries that voted favorably were the US, Russia, Brazil, and Spain. It may be because of the importance China places on their aircraft manufacturing industry.
If you are purchasing from Battery Bro there is absolutely no change in our logistics. We use cargo planes and official shipping labels.
Traders previously using passenger planes for reduced shipping rates will either increase cell cost or raise their shipping price accordingly. Chinese suppliers (Shenzhen, Dongguan, Guangzhou) may see less responsive supply as challenges in acquiring and shipping cells accumulate.
For the original ICAO April 1st ruling in Arabic, Chinese, English, French, Russian, and Spanish:
]]>Terminology for 18650 batteries can be very confusing. In this blog post I will clear five common myths.
I decided to go into some detail for each point so that readers may fully appreciate what lies behind each myth. With detail also lies some complexity. Admittedly I'm worried. I want this post to clear up 18650 battery myths, not confuse even more.
For that reason I added as many metaphors for phenomenon as possible. When you come across these, really take a moment to think about what is going on. I find these metaphors are really the best way to quickly grasp complicated concepts.
And lastly, if you come across any mistakes, have any questions, or disagree with something I've written, please let me know in the comments!
Answer: Technically, you have individual 18650 cells, not batteries
The terminology problem here arises because of the difference between consumers and engineers.
Technically speaking, an individual 18650 battery is actually a cell. A cell is the smallest packaged form a battery can take (and for 18650 batteries a cell is normally 4.2V).
The next step up in the hierarchy is a module, which can consist of several 18650 cells connected in either parallel or series. Modules can range in size from several cells to several hundred cells depending on energy requirements.
A BMW i3 lithium-ion battery pack, with viewable individual battery modules
A battery is a group of cells or modules connected together in either parallel or series, commonly referred to as a battery pack. Both engineers and consumers refer to the final package as a battery pack. However, only engineers typically refer to the pack with the single world “battery” in the context of lithium-ion 18650 batteries. 18650 battery packs almost always contain a BMS (battery management system), which is circuitry that regulates the cells and modules.
Do I really have to start calling them cells and not batteries?
Well it depends who you are and what you’re doing.
Calling an individual 18650 cell a battery, is completely acceptable for most people. We do it frequently on Battery Bro. This is because for most consumers, an 18650 is a battery just like an AA is a battery. It a little cylinder thing that gives us power - it’s easy to communicate.
But nomenclature for engineers is different. Concerns for efficiency dictate an adherence to standards and depending on their work philosophy, some engineers can take this quite personally. I have come across such, and do not disagree with them.
That is because typically a battery is a self-contained system capable of powering a device safely. The key point is battery safety. An 18650 cell on the other hand, needs additional regulation circuitry to operate safely because lithium is so chemically reactive.
The addition of a BMS is also critical to maintaining a li-ions expected long cycle life. Individual cells do not have a BMS, that is the job of the pack.
Remember the three tier system used in building battery packs - cells, modules, and battery. Each category has a different set of rules so they can’t share their names. So in some cases the distinction between cell and battery is necessary.
To recap, an individual 18650 is a cell, and a group of 18650s is a battery.
Answer: You can not actually compare the two.
There are two uses for the word LiPo (lithium polymer).
Many years ago, there was development of a chemistry dubbed LiPo. It never really was applied, and is not often menioned. In this type of cell actual polymer electrolytes are used - but it has not reached commercialization and is very much a prototype research cell.
Today, the word LiPo means Lithium Polymer. Polymer being a malleable, soft material that creates the external shell of the battery.
This is a bulging (decomposing) lipo cell (usually from age). Note an 18650 could never bulge like this.
Lithium Polymer (LiPo, LiPoly, etc.) is used for mobile phone and tablet batteries; think of their varying shapes and easy-to-puncture material. Contrast that with the steel-shelled 18650 cylindrical battery - which is standardized, hard, and cylindrical. 18650 (18mm by 65mm) batteries never share the characteristic of using a soft, malleable polymer pouch casing.
If we take a step back we can then see, that both the hard-shelled, and soft-shelled batteries use the same fundamental electrochemistry. They are both lithium-ion (li-ion, liion, etc.) batteries.
That is, they both give us usable energy by shunting lithium ions between the cathode and anode sheets. The ions move in one direction during charge, and in the other direction during discharge. This fundamental movement is present in both the hard 18650 and the soft LiPo type batteries. Both are lithium ion batteries.
Awesome, aren't all these different polymer architectures nice?
So what is polymer exactly? In ancient Greek, polus had the meaning “many, much” and meros “parts”. A polymer is a large molecule composed of many repeating subunits. This broad definition means there are many types of polymers - notably synthetic plastics, and other natural biopolymers like DNA.
That means even an 18650 cell without a polymer separator, or any electrolyte may still contain “polymer”. In fact lithium ion cells do have internal polymer but it accounts for less than 5% of the total weight and does not provide any electrochemical reactions.
This polymer is often a binding agent. It may be poly(vinylidene fluoride) or PVdF - which helps the mix of chemicals stick to the copper and aluminium foils inside the battery.
This binding agent shouldn’t be confused with the true meaning of lipo. Lip means “pouch format”.
Answer: When you charge a cell, its charge increases and not its capacity.
The distinction between charge and capacity is not intuitively clear so this myth arises.
The fuel gauge is a great way to think about battery charge
The easiest way to explain the charge is with an analogy to a fuel or gas gauge of a car. With this gauge you can easily compare the energy left in your car with the energy you had when it was full. The fuel gauge quickly lets you see how much energy you have left, until you need to recharge.
For batteries, this condition is called the State of Charge (SOC)(%), also known as the “Fuel Gauge” function.
Now think about holding your battery and asking “How charged is it?” It’s the same type of answer you expect if you ask “How much fuel is in my car?” That means when you are talking about charge of a battery, what you really want to know is its SOC (state of charge) - not its capacity.
To recap: When you want to see something like a fuel-gauge for your battery, you are asking about its charge, and not its capacity.
In contrast with the fuel gauge, buckets are a great way to think about battery capacity
The best way to understand capacity is to think of it as a bucket. A bucket in the middle of a sandstorm. Every day you can see how much water is in the bucket, and how much can be refilled. However, every time you open the lid, sand gets in and builds up at the bottom of the bucket. Gradually your capacity decreases as sand increases.
The bucket is capacity, and the water is energy. The sand is battery degradation (due to cell oxidation) which is a naturally occurring and irreversible process.
Jump to France in the 1780’s - a man named Charles-Augustin de Coulomb invented the SI unit of electric charge - which is now named after him. The coulomb unit is equal to the amount of electricity produced or consumed in exactly one second by one amp.
When we are talking about battery capacity, we are talking about its coulometric capacity which is derived from discharging the battery.
Coulometric capacity is calculated with the following formula:
*Discharge time is the range between its fully charged SOC to the cut-off voltage.
For example:
The resulting coulometric capacity is expressed in amp hours, or often translated to milliamp hours.
That is the equivalent of “I know how much space is in my bucket, if I drink it with a 2mm straw and it takes me 2 hours, I can say I have 4 millimeter hours left in my bucket.”
If you take this measurement when your bucket is brand new (no sand, no degradation) it is called rated capacity. If you take the measurement after some use, it is called current or actual capacity.
Environmental conditions like temperature and variations in amperage during charge and discharge can significantly alter the useable capacity of a cell. Think of the bucket analogy - if the water is too hot you can’t sip it at full speed. Likewise with brainfreeze on the other end of the spectrum. You can’t measure the bucket well unless the water is at or near its optimal temperature.
Furthermore,
SOC depends on capacity
The SOC reference can be either the current capacity or the rated capacity. Remember current capacity is what the cell or battery can hold, while the rated capacity is what it can hold when it’s brand new, in optimal conditions.
Using the rated capacity can be very misleading because of cell degradation over time.
Without accounting for the loss of performance from degradation, the fuel meter would always read 100% when charged, even if it could only hold half as much fuel as it could in the beginning of its life. Imagine if your fuel tank slowly shrunk over time, and car manufacturers did not tell you.
Charge is like a fuel gauge - it’s easy to see how much you have left. Capacity is the total amount of fuel you can carry. You can measure the capacity for any given SOC (state of charge) but it is only an estimation.
Answer: All 18650 batteries are secondary cells.
A primary cell is one that is not rechargeable (or can not be easily recharged) after it is discharged. Primary cells are like disposable plates - used once and then discarded.
A secondary cell is one that is rechargeable.
Secondary cells have become more and more popular and have replaced primary cells in many applications. However, in some use-cases like smoke detectors it still makes sense to use primary cells because their self-discharge rate is much lower.
Lithium-ion batteries are secondary cells, but they are used as primary cells were used in the past - for example when they direct power in laptops, mobile phones, and electric bikes. Even though li-ion is often used as primary cells have been in the past - liion is still considered a secondary cell.
Answer: There is little relationship between the two, and while they both function with the same purpose - the output (in Ohms) is always different.
To understand the difference between DC resistance and AC impedance you should understand that electrical loads have both resistive, and reactive phenomenon.
So keep these two things in mind:
Know these interchangeable terms:
Measuring internal resistance disregards the reactive elements.
Looking at the internal resistance of a cell or battery from a purely resistive value (ohms) disregards reactive elements. The best analogy I have heard for this is that of a heating element that produces heat by the friction (resistance) of current passing through. The more internal resistance, the more heat is generated. In this scenario there are no reactive components, only one resistive one determining the output.
When your voltage drops from use, this is because the battery current is flowing through its internal resistance.
The DC approach is dubbed: Internal Resistance
The first and most common approach is to load-stress the battery. You apply a certain number of amps for a certain given time (eg. 20 amps for 5 seconds) and measure the resulting drop in voltage.
This is like adding friction to the heating element from the previous analogy, and measuring its resulting increase in heat.
A note should be made regarding signal-to-noise ratio. Early DC tests required high-amperage for this reason. Imagine being at a cocktail party and trying to listen to a conversation across the room. It is only possible to do if the person is screaming.
The AC approach is dubbed: Internal Impedance
A newer, improved approach to measuring resistance came after the DC approach. Using AC power, battery scientists were able to send an AC signal through the battery at a very specific frequency. The frequency here is the key point.
If we go back to the cocktail party. Now imagine we are a dog, and the person across the room has a dog-whistle. This is what using a specific AC frequency can do - it can allow us to very accurately discern the signal from the noise with a unique signature.
The problem is that this AC ripple will interact with other elements of the battery (inductive reactance from coil, and capacitance reactive from capacitor) which will degrade the signal quality. This is akin to the dog whistle bouncing off the walls and people.
There are newer approaches where high amperage is no longer required, and tiny amounts of pulsed current can be applied to accurately discern the signal. This is akin to now being able to clearly hear a butterfly flap its wings across the room at the cocktail party.
As we can see, the DC approach to measure internal resistance does not measure anything reactive. It is like a heater, you have more friction and you have more heat - there is nothing else. On the other hand,- the AC ripple reacts with coils and capacitors. One utilizes a DC load, the other an AC signal.
When measuring an 18650 battery or cell, it’s important to note which approach you are using because the resulting ohm values will be different.
Comparing resistance to impedance is not comparing apples to oranges - they are different non-interchangeable terms.
And that is the end of these five battery myths. Here is a recap of the myths and their answers:
Automated warehouse for small electronic parts
In this blog post, rather than do my own testing - I will rely on the specification sheets provided by Panasonic, Samsung, and LG. We'll look at the storing section of these spec sheets, and break down the important factors and what they mean. Scroll to the end, the overview, to get to the conclusions of the post quickly.
A Panasonic NCR18650B 18650 cell
Storing Conditions | less than 1 month | -20 ~ +50°C | Percentage of recoverable capacity 80%* |
less than 3 months | -20 ~ +40°C | ||
less than 1 year | -20 ~ +20°C |
*= (Discharging time after storage / Initial discharging time) *100
The discharging time is measured by the discharge current of 0.65A until 2.5V of end voltage after the battery is fully charged at 25°C.
There are three rows, each with different storage conditions. Note the second and third column are locked in place by the fourth. Each row represents recovering 80% of the battery's usable capacity. Since the rated capacity of the NCR18650B is 3200 mAh, this 80% represents 2560 mAh after storage.
In the last case, storing for one year with a 20% drop in capacity translates to 1.6% loss of capacity per month, or 53 mAh.
In the first case (storing at high temperatures for less than one month) translates to a loss of 21 mAh per day.
We can see from the above 3 items, it is temperature as the main factor determining the resulting capacity after storage, and ultimately how long you can store your battery for.
18650 batteries can be stored at very low temperatures, but high temperatures degrade them quickly. Rule of thumb: They must always be stored at less than 60°C.
Lithium-ion batteries, in most cases must maintain a voltage above 2.5V before they start to break down and decompose. Therefore, for long-term storage it is best to "top-up" your batteries when their voltage drops too low.
A close-up of the 25R top cap (positive terminal)
Storing Conditions | less than 1 month | -30 ~ +60°C | Percentage of recoverable capacity 90% |
less than 3 months | -30 ~ +45°C | ||
less than 1.5 year | -30 ~ +25°C |
The Samsung 25R performs better during storage on all fronts. Across the board, the 25R can store at ten degrees lower than the 18650B. As well, the difference in higher temperatures, in favor of the 25R from 1 month, 3 months, to 1.5 years, is +10°C, +5°C, +5°C.
Most importantly, this 18650 battery can be stored a full six months longer and retain 90% capacity (10% more than the NCR18650B).
The 25R spec sheet notes that for long-term storage, the voltage should, rather than be fully charged, set at a lower, more optimal voltage. This is to prevent the degrading of performance characteristics. In the case of the 25R, the recommended voltage is 50 ± 5% of its standard (4.2V) charged state.
Other batteries have different ranges, but most are close to ~50% voltage which is usually around ~3.7V.
Storing Conditions | less than 1 month | -20 ~ +60°C | Percentage of recoverable capacity 90% |
less than 3 months | -20 ~ +45°C | ||
less than 1 year | -20 ~ +25°C |
It is good to reference at least three batteries, and off the blog I have checked more. All 18650 batteries researched need a storage range of between -20 ~ +50°C (-4°F ~ + 122°F) or they will degrade, so this is a good rule of thumb to use.
Also keep in mind the maximum temperature for storage should never exceed +60°C (140°F). It is better to store in a cold environment, than a hot one.
Optimally, a good storage temperature should be closer to 25°C (77°F) or a somewhat lower. The closer you are to an optimal temperature, the longer you will be able to store your batteries without "topping up" and recharging them.
For the most part, the maximum time for 18650 storage before recharge is about one year.
If you are intending long term 18650 storage, a storage charge closer to 50% of usable capacity (~3.7V) rather than 100% (4.2V) will prevent faster battery degradation.
It will cause a loss of performance and your cells may leak and/or rust, and ultimately become unusable. Cells becoming unstable enough and exploding in storage is a possibility. In the worst case - explosion - it is not clear why this sometimes happens but it could be due to static, pressure, temperature, or packing incorrectly (allowing metal objects or batteries to touch).
His device was a mechanical mod, not a regulated mod. If you do not clearly understand the difference, please take a few minutes to get these points down.
A mechanical mod is as simple as it gets, and is dangerous for newbies
So when does it get dangerous?
Since there is no protection circuitry, a user can easily stress the battery in terms of:
All of which, can cause a battery to smoke, fire, or explode.
A regulated mod is more complicated, and much safer for newbies
This is the actual mod from the incident, captured by WINK news
A man in Naples Florida was burned both externally and internally by an exploding battery. The lithium-ion 18650 battery was inside of his mechanical mod. He was vaping as normal - when it exploded.
His sister found him not breathing, with a badly burned neck and face. The mouthpiece of the device possibly shot down his throat and exploded again (however this is not confirmed, just a possibility at this point.)
This particular mod did not have any protective circuitry that could have prevented an accident like this.
First, before selling a device the vape shop owner must clearly assess the level of expertise the end-user has. An unregulated device should only be sold to expert level users.
A vape shop owner must use their own discretion when assessing the ability of and end-user. Some helpful questions to ask are:
After assessing the ability of the end-user, the vape owner should spend several minutes going over the details of battery safety. Spare no expense. This will not scare off your customers, it will do the opposite - create trust and a sense of authority for your shop. Preventing accidents should be any vape shop’s number one priority, always.
You may also ask Battery Bro about our safety booklets. If your shop would like to start add battery-safety as part of your customer experience we would love to send you 50 free safety booklets.
]]>LG Chem
LG Chem has announced the building of a lithium-ion factory in Europe to mass produce li-ion batteries for electric vehicles. Europe has so far been supplied by a mix of Chinese and Korean cells.
A battery factory in Europe means two things. First, the growing demand for lithium-ion is evidenced by this move - and electric vehicles using over 2,000 individual cells each are reported as the main driver of demand.
The second thing is that the European battery market will soon get a better supply chain. Better because some Chinese suppliers can be potentially cut out as European wholesalers crop up. Quality control will likely improve, logistic difficulties (air shipping) will be reduced, and the overall life cycle of the cells are likely to go up as a result.
At 2,000+ cells per electric car, even a slight improvement to a cell’s capacity and life cycle will be multiplied and magnified.
Just how many batteries will this factory be able to produce?
The factory set to open in Europe will have an expected capacity of 50,000 batteries per year. And it will probably open in Poland where LG has many of their European headquarter buildings already up and running.
Slightly unrelated: I found this picture when I Googled "Negev Desert". This is a solar trough which is actually a parabolic mirror that collects sunlight on its focal line. This particular one has a tube running along the focus.
The Facts:
Surrounding the tower are 50,000 computer-controlled heliostats. [Etymology breakdown:Helio means sun, Stat means stationary. First use: "an instrument for causing the sun to appear stationary" (1742)]
Each of the heliostats will slowly track the sun as it passes overhead of the mirrors throughout the day from dawn to dusk. This slow movement will be powered by lithium-ion battery packs. Each heliostat will have its own battery pack. Each battery pack is meant to last for 25 years before needing replacement.
Normally a centralized battery would be considered first as lithium-ion batteries perform best and last the longest when they are in a temperature controlled environment.
On the flip side, since each unit is self-reliant, one failure will not make a big difference and will not need to be fixed immediately.
In the end, the most important reason to give each heliostat energy independence was cost. If you have not figured it out yet, removing all cabling from such a system is the answer - and an insanely great way to remove complexity, and associated costs.
One of the battery modules Nissan produces
Recently this story came out where you can see a bit inside a battery factory. Here are some highlights from that article:
Quote: “There is only one step in the process where an employee actually touches the battery,” said Chris Whitaker.
Now here is a really interesting one. On each battery is a code - that code obviously does quality control, tracks location, manufacturer date and so on of each cell when it is looked up. We have all seen a line of random numbers, symbols, or something that looks like a QR code on our batteries.
Nissan pointed out their codes track everything including the humidity of a cell on a certain day after it started “baking” to its particle count after finishing baking. The amount of data stored per cell is likely far beyond what the average consumer expects.
Here are some more facts:
To see all the pictures, please visit the original article.
]]>The BEAST 18650 battery in a new Battery Bro case.
Battery Bro was founded about a year ago with one intent - to fight against fake and dangerous batteries. Since then we have grown but kept this core value.
We’re quite content selling brand name cells and building custom battery packs. But there is always an unusually high number of emails that we get that go something like this:
“Hello Battery Bro, I want some 50A cells because they are the best.”
or
“I know 35A batteries are the best, and you are telling lies!”
The problem is, a really large group of people are skewed to the side of believing extreme amp numbers. There are a number of reasons for that:
But, it happens time and time again.
There really is only one way to solve this problem, and it’s not solely education. It’s a battery brand. So the first aspect of BEAST is that it is really the battery brand you can trust. All of our cells are checked for authenticity and grade. The chosen cells are curated as being the highest-tech and most reliable.
The BEAST vape battery in a mod. Behold the electric squid.
We like to think of this as the Popeye factor. If Popeye were a robot he wouldn’t want spinach - he’d want BEAST batteries. Something he can always rely on, and something that is more powerful than anything else.
The second factor with BEAST where we thought it would be interesting to experiment in was with artwork.
No one has produced art batteries before. Batteries should look badass, just like all your other gear. There is no reason for a battery in a high-priced device to look like crap.
We are informed by Samsung, Panasonic, and LG on release schedules for new batteries. After they go through some months of testing in the real-world we decide if they should be wrapped by a BEAST or not.
BEAST batteries are first covered in a 3M adhesive sticker and then wrapped in a heat-shrink clear PVC. This is the Kraken-Z model, rated at 20A is a rewrapped Samsung 25R5. Note: no fake ratings. Ever.
We only use world-class artists. Like our first artist Frank, who has made artwork for games like Deus Ex and Star Wars.
The designs for all BEAST batteries after the Kraken (first model we make) will be voted upon via Reddit.
A special 3M paper is printed on which does not insulate heat at all. Normal printing paper would, so this is one big difference to emphasize. Our wraps will not make your batteries hotter than normal - whereas if you print one at home it will (by about 5 degrees Celsius).
At the heart of things, BEAST is still an experiment. We are making BEAST to solve a problem. There are really no gold standard vape batteries on the market. Everyone knows the brands that exaggerate their specs. They all look like crap, and are absurdly dangerous.
It’s hard not getting ripped off. We want BEAST to be the safe option. Just like Popeye’s spinach.
View full thread here.
]]>This is LG's new brown battery - the LG HG2
A post on the HG2 is long overdue.
While the original release of the LG HG2 was in 2014, production has become available in Summer 2015. A 20 amp, 3000 mAh milestone is, in some way a holy grail of stats. A battery that can both be high-drain, and high-capacity is just what everyone wants. The LG HG2 can be seen as a 500mAh capacity upgrade from its predecessors the HE2/HE4 which also have a 20A discharge limit.
LG Chem is on a rolling schedule of releases and research, all planned years in advance. An average of between 6% and 10% increase in battery performance is expected, compounding yearly. That means, taking into account the battery specs and LG Chem's release schedule, the LG HG2 will likely be a good contender for one of the best 18650 batteries for some months to come for high-drain applications.
That said, there are many cases where the newest 18650 battery with the latest specs never gains mass adoption. That can be due to a number of reasons including a quick upgraded release, unforeseen safety problems, supply chain insecurity, market ignorance, and so forth. It's for that reason I am not crowning the HG2 as the new king on specs alone.
To test that claim, I'll do the standard Battery Bro review:
2.1 Capacity
3,000 milliamp hours is the highest capacity ever for a true high-drain (20A+) cell. If you are interested in maximizing both amperage and capacity you should consider this cell because it doesn't get better at the moment.
2.2 Nominal Voltage
This is the standard voltage for all 18650 batteries. (3.7V 18650 batteries are older, a standard of measurement was changed but actual voltage remains the same.)
2.3.1 Standard Charge
A 1.5A standard charge is good.
2.3.2 Fast Charge
A 4A fast charge is also good. However keep in mind that fast charging will decrease the cycle life of the HG2.
2.4 Max. Charge Voltage
Standard, no comment
2.5 Max. Change Current
N/A
2.6.1 Standard Discharge
These are normal standard discharge values. The nominal capacity of the HG2 is determined while discharging at these values. When discharging at its max. continuous discharge rating the capacity will be slightly reduced (watt hours more so).
This has likely led to the claims that the HG2 under performs. However many of these tests neither distinguished between the standard discharge vs. max. discharge testing conditions, nor did they take into account fast discharging conditions outlined by LG Chem in the spec sheet (see next section).
2.6.2 Fast Discharge
The Fast discharge has been tested at both 10A and 20A. What is important to note is the cut-off voltage of 2.0V. LG Chem’s testing conditions for rating Fast and Max. discharge values are as follows:
Cells shall be charged at constant current of 4000mA to 4.2V with end current of 100mA. Cells shall be discharged at constant current of 10000mA and 20000mA to 2.0V. Cells are to rest 10 minutes after charge and 30 minutes after discharge.
2.0V is considered the lowest possible safe cut-off voltage for discharging any 18650 cell. Most 18650 cells cut-off at 2.5V. This 0.5V difference translates to a higher milliamp hour rating, but at expense of utility. (We see a similar parallel between the LG HE2 and HE4 fast discharge conditions).
Most people do not want to go below 2.5V for safety concerns, and if they do the low voltage environment does not provide ideal performance.
2.7 Max. Discharge Current
A 20 amp cell - very good.
Note that this is the cell's maximum continuous discharge rating. Some people seek pulse ratings, which are often fabricated.
Remember: a pulse is defined as current over time. Without stating time, pulse lacks meaning. An example of a proper pulse rating would be 30 amps for 2 seconds. A cell rated at anything above 30A, without an attached unit of time is, in essence meaningless. None of the big three (Panasonic, LG, Samsung) make an 18650 battery rated at over 30A.
2.7 Weight
(Maximum weight)
2.9 Operating Temperature
Standard, no comment
2.10 Storage Temperature
Standard, no comment
Here is the top-cap, or positive terminal of the HG2. Note there are four top-cap connection points on LG 18650 batteries.
There should be no rust, discoloration, spots, burn-marks, excessive scratch marks, or anything else out of the ordinary. As this cell has been recently produced (Summer 2015 batch), they are new and the steel will reflect that. If your new HG2 has any of the abnormalities listed above, request a return with your vendor and suspect a counterfeit battery.
This is the negative terminal, or bottom of the LG HG2. Nothing abnormal here. There are a few scratch marks (usually circular) on the bottom even on brand new cells. This is normal and from production, as the cells are tested and charged and the steel scratches easily.
Height: 65.1mm - check. (Do not do this with metal calipers as you may short-circuit the cell.)
Width: 18.5mm - no problems here. If you are making a pack, note they are a little bigger than 18mm.
Weight: 44.86g. Let's call it 45g from measurement error. Where does that leave us? With a max. specified weight of 48g - it leaves us just fine. Albeit I will weigh a few more later just to confirm, a 3 gram discrepancy from maximum value does not cause alarm.
Accounting for the test's environmental temperature. This is five points off an ideal temperature (LG Chem's test opted for 25 degrees C), but at this difference the efficiency loss is negligible and I will go ahead.
I enjoy charging my 18650 batteries on the VC2. The big display just makes my life better.
This is our 18650 discharging unit. The readout is volts (that last digit is a V and not a U if you were wondering). As you can see this battery is running out of juice, and the discharge test is almost complete. This unit runs off of USB power and as such it has an unfortunate current limit of 3A.
For the first discharge test I used a 2.50 amp current with a cut-off voltage of 2.50V. The capacity is 40mAh hours short of the rated capacity of 3000mAh. Does this mean the battery is not meeting its rated stats?
Yes and no.
Here's what I mean.
The Yes
For one, the cell in this test is a few months old. A lithium-ion battery will lose some capacity every month it sits in storage. When we are concerned about 40mAh, some of that is attributed to its age.
I could also tweak my testing environment to fit LG's testing conditions by:
The No
Having said that, calling this a true 3000mAh battery is stretching the truth. It is more accurately stated as a 2960mAh battery.
Discharge test two confirms the HG2 capacity at ~2960mAh.
For discharge test three I changed the current to 0.50A. As you can see, at lower amperage discharges, the capacity goes up. (In this case, about 6 mAh were gained).
In this image I overlapped the 2nd (2.5A) and 3rd (0.50A) discharge test so you can see what is really going on.
If you look at the bottom-right of the chart, the difference along the X-axis (mAh) is small.
However the Y-axis of Voltage shows a bigger difference. You can think of this as the batteries lasting about the same amount of time, but the low amperage one gaining more working power. A higher voltage for longer results in more watt hours. The watt-hour rating can be argued as just as important as the capacity (mAh) rating.
There are three markings to be found on this particular LG HG2 battery.
These are quality control markings and likely batch identification codes. If you unwrap your HG2 and notice it has very different markings please leave a comment describing them.
Here is another look at the top-cap in all its glory, this time without the heat-shrink PVC or washer.
In the beginning I claimed the HG2 may be the best high-drain battery available right now. Unfortunately the cell I tested does not quite meet its mark at 3000mAh. It however does clock in at 2960mAh.
Even if we call it a 2900mAh, or a 2800mAh battery - it still surpasses the Samsung 25R (2500mAh) and the LG HE2 (2500mAh).
There are cases which this can be shown wrong, in particular in high-drain tests at 20A which I did not perform. It is however, highly unlikely that the capacity will be effected enough so that it can not exceed 2500mAh.
It is for that reason I am fairly comfortable claiming the HG2 is quite a beast, and I crown it as the current king of high-drain.
]]>Boeing aircraft factory
For this week in lithium-ion news I want to highlight the three stories I think are the most interesting. Battery technology is part of a complicated system with far reaching complexities. One critical component, is shipping them. As many people in the industry know - shipping lithium-ion batteries is by far the most difficult and most dangerous legal good to ship in the world. That’s right, your beloved batteries are savages unfit for airplanes - more dangerous than ammunition and fireworks combined. They are thought to have brought down passenger planes which have taken hundreds of innocent passenger lives in recent years. Is it all bad though? Isn’t there a better way?
Earlier this week Boeing released some statements about shipping li-ion batteries - and some of the information is not old and rehashed. The rehash goes like this - shipping lithium ion batteries on passenger planes is dangerous. Especially bulk batteries, as they can cause extremely hot lithium fires and thermal run-away events (a chain-reaction of lithium-ion batteries overheating).
What is new about the message is that for the first time, Boeing has formally urged every airline in the world to stop bulk battery shipments of lithium-ion batteries on-board passenger planes. Enough time has passed and substantial evidence has been collected - so large airliners like Boeing have realized such a danger is bad for their industry and airline.
They are pushing for more thorough safety standards, which includes some kind of protective packaging which can stop lithium fires. The equipment must be able to withstand thermal runaway events which yield really hot fires (an excess of 500 degrees Celsius ignites such an event) and a change in the chemical nature of the atmosphere within the plane's cargo hold.
On the other hand, the PRBA (Rechargeable Battery Association) agrees with Boeing but notes, that in the last 25 years no properly labeled and packaged lithium battery shipment has gone awry. They apparently do not know of a single incident where a li-ion battery malfunctioned on board an aircraft when it was put there under the proper protocols.
If this were entirely the case, airlines might not need better fire suppression systems - they just need stricter rules for their transport. In my own experience lithium-ion batteries are already extremely regulated and hard to ship. Offending countries such as mainland China have much looser shipment rules (people always seem to look the other way) as opposed to a port like Hong Kong where everything is done according to the books. More scrutiny should surely be payed to countries where the rule of law is more relaxed. Having said that - many readers including myself know the solution here is not in the books. Cultures with more relaxed attitudes towards things like packaging safety will almost certainly always offend. And then, it comes back to what Boeing said. The only sure-fire way of protection is to regulate - no more lithium-ion batteries on-board passenger planes until they can adequately suppress the fire if things go wrong.
Regardless of the solution, the aviation board will review this case in a few months and if a solution hasn’t been found (it very much certainly might not be, as the tooling is so expensive and putting out lithium fires is difficult) then the industry will be forced to only use cargo planes and sea freight. For consumers it might mean more restrictions, however the rulings will likely only affect bulk battery shipments in the thousands.
Battery Bro respects Saft, because they make some of the world’s best lithium-ion batteries. So good in fact that many are exclusively for use in space - on satellites, probes, and even rovers.
Space geeks might rejoice knowing that the ExoMars project is well underway and Saft was just awarded about a million dollars to test lithium-ion batteries for their use on the next Mars rover.
But first, let’s talk more about what exactly ExoMars is so we can understand the rover more. ExoMars stands for Exobiology on Mars, which is a partnership between the European and Russian space agencies to explore life on mars, in particular to find biosignatures of past or present life on the red planet. Thus it is classified as an astrobiological mission and its chief explorer - the rover will be launched in 2018 on a Russian heavy lift Proton launch vehicle (UR-500).
The mission includes satellites and other things of this nature to prepare for the rover launch. But the rover is the bread-and-butter as it gives us the closest thing to the capabilities of a human scientist on the planet’s surface. The rover is going to have something called a “Pasteur analytic laboratory” for checking out potential life, as well as a suite of tools like rock drills and so forth. Like with other missions, there is a good chance of luck - and likely the landing site selection will be the determiner for finding life.
This is a render of the rover that will use lithium-ion batteries from Saft
Powering the rover
To do all this, it needs a source of power. Like many things in space, the rover will use solar panels instead of a nuclear reactor. This choice is usually for safety concerns - because if the Proton rocket fails and explodes in Earth’s upper atmosphere the radiation fallout could be potentially lethal. So we stick with solar.
In this case the rover will get 1200 Wh of working power and 1142 Wh in nominal battery capacity - which is enough to allow the rover to run continuously and uninterrupted throughout the dark nights on Mars. The cell of choice right now is the Saft MP 176065 integrated xtd cells.
Any battery fit for a Mars rover in 2015 has interesting specifications. To look at the cell’s spec sheet please visit this link (http://wamtechnik.pl/files/specs/839.pdf).
Here are some quick specs for your reference:
But these are not ordinary 18650 batteries, Saft custom makes them for space so there are certain features that make them ideal.
For example, let’s look at some of this battery’s key features:
And while each cell is technically an 18650, the whole battery (pack) has features particular to its mission to Mars. That includes mechanical and electrically integrated battery management systems (BMS).
They also market the 176065 battery as longer lasting. However there is no indication of that on the spec sheet. If the life cycle is similar to other 18650 batteries, it may be limited to less than 500 cycles (at 80% capacity) but continuing past this performance mark it will likely last thousands of cycles. Each cycle might translate to a night on Mars, so a battery system using lithium-ion on the rover will probably last years. Some chemistries can easily last ten times as long, so rating them for ten years or more by my speculation is not far-fetched.
I think at this point, people will just write about Elon Musk and it doesn’t matter what about necessarily - it will get attention. Regardless of the perhaps over-saturation of articles about one guy - they continue to be quite interesting. Especially for people like us at Battery Bro that are interested in such things as lithium-ion batteries.
The new Tesla model S is being framed with phrases like “ludicrous speed”. And well, it’s true the latest batteries are really fast, and can last even longer.
The main cause of this transformation is the inclusion of silicon into the battery anode. You might be spitting coffee all over the screen if you are a proclaimed battery guru. You know many 18650 batteries already have had silicone in them - and it’s true. You can find the papers and supporting theory just by searching Google. However it seems this particular element is a little bit special. And Tesla plans to include more and more of it in the anode to replace the currently popular graphite.
It is also supposedly the first time a lithium-ion battery with a silicon-based anode has been used in an electric car, or at least a mass-market one. So in this sense it is a little game-changing. If it’s not the end result that people will admire, it’s the process to arrive there. Can you think of any other automobile company at the fringe of battery science? Not really, and that’s what makes Tesla so unique.
So what’s special about a silicon anode? Why choose silicon over graphite anyway?
So, do the math. Silicon must be the solution, there is no other way. Stick with graphite and you have to deal with the obvious disadvantage. It is a bottoms-up approach to fundamental physics. For the added amount of lithium ions the silicon can store, a single battery would be able to transfer far more lithium between anode and cathode. Simply speaking, that translates to a higher capacity.
There are problems though, and some interesting things still need to be overcome. My favorite is the “swelling” problem. That is, when lithium ions shuttle into the silicon anode, the silicon gets fat - four times its normal size. When this happens, the battery will immediately die. It will shatter, and that’s that.
The second disadvantage to such an anode is that after all is said and done, it works down to only about a 10% increase in overall performance (non-linear increase in performance). So it is a lot of small gains and tweaks, over years, that will really make a difference to electric vehicles. This is just one of many.
]]>The nickel-based battery system used by the London Underground
Batteries are already used on many trains as a backup power system. The London Underground uses batteries on all their trains for this reason. If it were to stall or need emergency power, the batteries can provide enough energy to bring everyone to the next terminal (as well as for radio, controls, and other electronic devices like the broadcast and security systems). Basically the train stays on. These are not lithium-ion batteries however, they are a nickel-based. Because they are public, backup batteries - metrics like longevity and upkeep are favored. The cells made by Saft only need to be topped up once every two years and will last up to fifteen years.
Saft does not only make nickel-based batteries for the metro - they also make more exciting lithium ion batteries, especially for space and defense. They have a slogan “powering outer space for half a century” which is pretty cool, as they powered Galileo (the first li-ion batteries for permanent constellation) and have put a grand total of 30,000 lion (1.3MWh) of cells into space. But that’s for another post.
Having a subway that runs on specifically lithium-ion batteries is possible. The Kawasaki Municipal Government now has goals to do this, and they want to start building cars this year. It’s going to be a 17 kilometer line to like the north and center part of a city. So, a minimum viable product with good societal impact. Many of the more exciting transportation advances are only for relatively short distances, like the Hyperloop. The technology does not exactly exist for a Japanese electric train yet, and rather than start from scratch the team behind this project is scoping out the Eliica.
If you haven’t seen or heard of the limousine-sized Eliica, now is your chance. It’s a prototype from 2004 that runs on lithium-ion batteries and can do excellent acceleration as we now come to expect from EVs. It got attention for breaking some speed records - and it has something interesting called wheel hub motors. That is, each of its eight wheel hubs is mounted with a self-contained motor system.
[A side-note on the Eliica’s battery specs]
The Kawasaki train may also employ wheel hub motors. I’m sure there are certain factors about a train which play into the efficiency of such an idea - the length of the train being one. As with all electric vehicle startup projects, the project managers noted battery capacity, and speed were their largest markers for improvement. A government tends to look farther into the future than say, an individual like you or me. An 8% or so increase in lithium-ion battery efficiency every year seems slow, but in a 15 year timeframe it is very quick.
Something else trains are good at is regenerative braking like you’ll see in the Prius, Model S, and other vehicles. While it has been used for a long time, for one reason or another is hasn’t caught on in the US until recently. Just last week, Philadelphia showed off their new hybrid subways that do this.
The energy is not received directly by lithium-ion batteries, but instead are met by supercapacitors first as a buffer. The supercapacitors (also sometimes known as ultracapacitors) can store high amounts of energy very quickly. They can then safely drip that energy into the batteries for more efficient discharging. The supercapacitors are also more of a permanent fixture - being able to last between 30,000 and 1 million cycles. This is perhaps the future of lithium-ion batteries, but for now li-ion is generally under 500 cycles. Supercapacitors are also about ten times more expensive.
The Philadelphia subway will make some money back by feeding the excess energy directly into the grid.
]]>Those two blue boxes hold the Volt batteries that power an admin building
Old Chevrolet Volt batteries are helping to power a high-tech building in the new General Motors Enterprise Data Center. Managing a data center is all about managing its energy consumption. Making completely green and sustainable data centers has always been a foremost use of li-ion in buildings. That is because lithium-ion batteries are so often paired with solar energy. As panels collect the sun’s energy, the batteries store and hold it for later use.
The friction preventing mass adoption is caused by price. The cost per kilowatt hour needs to decrease before it will see full adoption. However small research projects, the pioneers, have already popped up. In Milford, Michigan, the General Motors Data Center has linked up five Volt batteries with a solar array to power administration offices. The batteries are also fed by two wind turbines which continue powering the batteries in the dark.
The Volt’s batteries, like most 18650 batteries, are rated until 80% of their rated capacity has been reached. This capacity decrease happens over time, determined by the cell’s cycle life. An 18650 cell typically has between 200 and 500 cycles. This cycle life increases year by year, which is an often overlooked factor directly influencing their price.
This data center will probably soon be powered by lithium-ion batteries too.
While 80% of capacity is bad for car owners, who depend on that high-voltage energy of a new battery (mainly because it influences driving range), it is great news for buildings. Lithium-ion batteries can often run thousands of cycles until they are completely useless. The recycled Volt batteries may be able to effectively last between a year and two more before their capacity is reduced beyond their utility.
An inside look at the Volt batteries.
Why is this interesting? In the short-term, projects using old Volt batteries will be relatively inexpensive. As more electric cars are produced, it is likely more used EV batteries will come to market. If we measure cost per kilowatt hour without minding accessibility of the cells, the used volt batteries can bring the world in a sub $200 range. However used Volt batteries are not applicable for many uses - most notably in electric vehicles (the industry forecasted to eventually be the main driver of demand). See how that works? They are also not readily available, and manufacturers wishing to build custom packs with the cells have the difficult prospect of unreliable supplies.
Used Volt battery specs (as of June 27, 2015)
This works out to, ~$166 per kilowatt hour, and is applicable to industries like home energy. This cost is even lower for large manufacturers. Remember the goal for batteries is not to make them cheaper, exclusively. 18650 lithium ion battery prices have remained the same, however an increase in energy density means the same sized cells hold more energy and last longer than before (about an 8% improvement per year).
This line of thinking is challenging however. As pointed out earlier, used car batteries are very cheap in terms of kilowatt hours - but they are not a great source of information to evaluate a formal “cost per kilowatt hour” metric everyone likes to refer to. A better metric would disregard used batteries as a secondary market and focus on the primary driver - the 18650 battery.
The 18650 battery is the most produced cylindrical lithium ion cell. It is used in the world’s laptops and in Tesla cars like the Model S. A brand new 18650 battery (one that is the highest capacity like the Panasonic G series, or MJ1) that is accessible in smaller quantities for anyone who wishes to create a custom pack - is a much more qualified candidate to determine such a metric as cost per kilowatt hour.
So when people say used Volt batteries have exceeded a limit placed on mass adoption for lithium ion, they really need to look closer at the definitions used. A better metric would only include the used Volt battery as a side-note and focus on the commodity 18650 battery.
The research station has proved that home energy for sub $200 per kilowatt hour is possible. This technology is immediately applicable to those in rural parts of the US or abroad that want to stay off-the-grid. Companies can also decide to become self-sustainable and earn a certificate like the LEED Gold certification with projects like this.
There are numerous regions with severe whether and unpredictable power which can use such a system as a town-wide UPS. At that point, it becomes an economic matter as decreased productivity from blackouts can really cost tourism or mining a lot of money (think ski resorts).
Mining can benefit from lithium-ion driven energy storage right away. A small handful of companies operate a majority of mines, so the distribution network to supply such an industry is fast. Mines are often physically far from being able to tap into the grid and being entirely off-the-grid makes economic as well as environmental sense.
In the future more and more building systems will become energy independent. The limit will probably not be reached for 25 years. Until then, more and more buildings will take responsibility for their footprint with novel energy storage solutions. There will always be pioneers - in this case we’re talking about the first use-cases of used electric vehicle batteries being implemented. But soon there will be settlers, and this type of approach to energy will become mainstream.
]]>The LG MJ1 model is INR18650MJ1. It is a rechargeable lithium ion battery, just like all other 18650 batteries we review on Battery Bro.
The MJ1 is new, that is why it is exciting. Every new generation of batteries provide just about an 8% increase in capacity (generalized) over those of the previous year. The MJ1 is certainly no exception, as it's nominal capacity is of the highest of all 18650 batteries on the market, and it achieves this without sacrificing much of its maximum discharge rating.
Let's take a look at its official specifications:
As you can see, the MJ1 really boasts a high capacity - 3500 mAh. A max. discharge current of 10A means the battery also can pack quite a punch. This is good news as it is proof that battery scientists have really started closing the gap between capacity and max. discharge rating.
400 cycles is a good lifetime, and will mean these cells may be able to last up to two years or more depending on the application.
The capacity was tested under the following conditions:
Voltage
The total safe voltage range for the LG MJ1 is between 2.50V and 4.20V. However, for many purposes it is best to recharge the battery before it discharges to 2.50V. Many people prefer to keep their lithium ion batteries charged above 3.0V.
Temperature
For what it's worth, 23 degrees Celsius is a slightly lower than most optimal temperatures. Most 18650 batteries are tested at 25 degrees. Your temperature will effect your battery's performance, and the farther you deviate from the optimal temperature the greater the loss of efficiency and overall capacity. 18650 batteries should not exceed 60 - 70°C, and should not be charged when below freezing.
Tapering
Charge tapering is what lithium-ion batteries do to get as high-voltage as possible, as safely as possible. To taper means to "reduce towards the end" which is what a high-quality charger does when reaching a voltage close to 4.2. It gradually reduces the amount of current put in the battery as it reaches the end of a charge cycle. If you are still wondering what is charge tapering or if you want to learn more I recommend this short paper titled Battery Charger Termination Issues. by Texas Instruments. Most 18650 chargers on the market do not have great tapering, and as such charge termination suffers. This leads to a shorter battery life, and less capacity in the long-run.
Discharge current
The standard discharge current is .2C. To find out what this is in amps, take the nominal capacity (3.4Ah) and multiply it by the C (maximum safe discharge capacity, where C stands for capacity) rating. That is 3.4mAh multiplied by .2C = .68A. For those readers working on electric vehicles, this is the same discharge conditions as the Panasonic 18650B. You might think this testing condition is low, and you are right it is the minimal viable current draw, which is where capacity ratings come from.
However the MJ1 goes a step further and also defines testing conditions for high-drain and fast-charge conditions:
Letting the MJ1 rest
Something worth noting if you are using the MJ1 for high-drain and fast charge (which most of you will probably take advantage of) is that LG Chem recommends that cells are to rest 10 minutes after charge and 20 minutes after discharge. Take note of this if you are doing cycle-life tests.
Storing the batteries
Storing the batteries, whether in a bunker or a warehouse should be done their maximum voltage (4.2V) and charged as per the standard charging conditions I outlined above.
Take your battery and look at the top, sides, and bottom. Look for:
The color of the PVC I would call a standard green or shamrock green. No blue or yellow hue at all.
The bottom or negative terminal (pole) of this 18650 MJ1 battery. Not unlike most other unprotected 18650 cells - just flat, unfettered steel.
The metal positive terminal (pole) of 18650 batteries produced by LG Chem always have four connection points to the top cap.
Quality control codes on the steel case can be seen through the translucent PVC skin.
The max diameter of the MJ1, and my actual measurement are both 18.5mm.
The max. height of the MJ1 is 65.2mm, and my measurement of 65.4mm is acceptable because it is inside the range of error for these digital calipers.
Important! Don't do this with metal calipers as it may short-circuit your battery. If you use metal calipers, you must make sure to insulate the ends with something like electrical tape.
The approximate maximum weight is 49.0g. My weigh in does not exceed this so everything is good.
Testing the batteries in an environment a bit hotter than optimal. It will make a little difference to overall capacity (but not too much).
This is the first discharge test I ran at 2.50A discharge current and a cut-off voltage of 2.50V. Noitce that the capacity does not seem to meet the spec sheet, as it turns out to be 3307 mAh.
Here is the second test, with the same parameters as the first. The capacity readout is the same.
For the third and final test I used the amperage discharge which the battery was rated with (.68A). This test slightly exceeded the minimum capacity of the MJ1 which is set at 3400 mAh. Also note the increase in total energy as the voltage remains higher throughout a lower current discharge (12.21 Wh, about one watt hour more than the tests at 2.5A).
Resistance
At the same time I can put a 1000mA pulse through the cell and get a reading of its resistance. A reading of 70mR is not bad, but this resistance is typically seen in high-capacity, low-drain cells. The higher resistance is one reason there is a decent loss of capacity in the higher-drain tests.
The MJ1 is definitely an exciting new cell for 2015. It will compete with the best Panasonic cells (like the G series) at the highest ever 3500 mAh. As we can see, my cell just barely meets this spec, and actually the cell's rating is closer to the minimum capacity of 3400 mAh. And that's in a minimum-drain situation. I feel that if given a full 10 amp discharge, the capacity would fall to 3200 mAh at this time.
I should also note this is a sample research cell sent to distributors like Battery Bro before it goes to market. The final production model should be even more polished and it should be given a second-look when that time comes in the next several weeks.
]]>Battery Bro was asked for clarification to distinguish between the blue 25R and the green 25R.
When requested, Samsung SDI responded with the following model names:
Bottom-line: The green 25R5 has a better cycle life.
A cycle is one full charge and discharge of the battery. If someone asked you how old a battery is, you should answer by telling its cycle count. So what is the cycle life the 25R? A quick check of the spec sheet yields the answer:
The 25R2's life is: 250 cycles. This is tested at 20A, the cell's max. continuous discharge rating.
After 250 cycles the maximum capacity the 25R2 can hold dips to 1500mAh or lower (this is at 60% of its starting capacity, at 25℃).
So we can say that the 25R5 has a cycle life greater than 250 under these same conditions.
Samsung listed three different chemical tweaks for the 25R5 - FEC, SN, and PA77.
This paper published in 2011 by the American Chemical Society describes the effect of FEC on battery performance in lithium-ion battery electrolyte compositions.
When batteries are cycled there are a small impurities, that over time reduce the capacity of the cell. This is why batteries do not last forever.
Every time you charge or discharge your 18650 battery (cycling), you are destroying nanoscopic structures that store bits of energy.
In this image you can see the structural and performance differences to an electrolyte with FEC added. The red (b) and green (c) lines include FEC, their lines never dip below a 1000mAh capacity, and the photos show materials which are structurally more complicated and precise. The black (a) line is nearly depleted by cycle 35.
Scientists look at the different morphologies of the battery chemistry with images like these. For fun, see if you can identify any of the following traits in the image:
In this paper, scientists created NiO (nickel oxide - a transition-metal) which is nancuboid (small, cube-shaped). The nice clean and sharp edges that make up the nickel oxide cubes are interesting because they are able to discharge energy at a high rate (high amp charge/discharge), and also store a lot of energy (high capacity). They applied FEC (fluoroethylene carbonate) as an additive to the cubed nickel oxide, which produced better cycling stability.
Some seriously awesome nano cuboids are shown here. These two images courtesy of the paper linked to earlier.
The FEC addition gives the nano-cuboids better performance, and the degradation caused by cycling your battery is lessened. They found NiO is relatively stable until its 35th cycle ,where a sharp drop in capacity is observed. The drop is attributed to the degradation of the NiO - particularly it undergoes a reaction that features large volume changes which cause cracks, reduce conductivity, and pulverize the electrode. When an FEC additive was introduced, great improvements to capacity were observed: the measurement being almost twice the theoretical capacity of NiO. The changes are attributed to nanoscopic morphologies but the precise reasoning is not well known.
Bottom-line: Adding FEC increases the cycle life of li-ion batteries.
This paper from 2014 describes the effect on a cell’s impedance (a measurement of resistance) when the electrolyte includes an SN (succinonitrile) additive.
In summary, adding SN to the electrolyte greatly increased the impedance (resistance) growth during cycling. As lithium-ion batteries age, not only does capacity go down, but internal resistance goes up. This makes it more difficult for lithium-ions to flow, and places added stress on the battery causing further degradation.
So the SN electrolyte actually increases battery resistance between cycles. By reducing the amount of SN in the Samsung 25R5, Samsung SDI has also decreased the 25R’s impedance growth.
Bottom-line: Decreasing SD will keeping resistance low, for longer.
Actually I can find no information about this additive in an electrolyte, so I think it is probably Samsung SDI proprietary research. They have increased the balance of the PA77 chemical in the 25R5 electrolyte, and I assume it improves cycle life in some way but I don’t know how.
Could the secret of the green 25R5 be... protactinium?
PA (protactinium) is very toxic and a highly radioactive chemical element, but is present in small amounts in most natural things. We eat it, drink it, and breath it. Government even regulates the amount of allowed PA in the atmosphere. Samsung SDI stated “PA77” as the chemical in the letter-of-guarantee, where normally the ‘77’ should denote the element’s isotope number. It is possible Samsung uses a special isotope of protactinium which is very stable called protactinium-77.
But there is no indication of this, anywhere.
Argonne National Lab, holds thousands of lithium-ion patents. They have invented some of the most widely used 18650 chemistries like NCR, and lease them out to others like Panasonic. Owing to the chemical protactinium's scarcity, high radioactivity, and high toxicity Argonne Labs stated in 2005 that PA has no use outside of scientific research.
So has Argonne started putting it in batteries since then?
It’s possible because I can’t think of what else the PA77 would refer to. If it followed the same naming convention as the other two chemical changes, all roads lead to this conclusion. However it may very well be something completely different. If you are a chemist or battery scientist that has a different idea, please send me a message! I would love to get to the bottom of this.
A reader has pointed out that there is no way protactinium could be in the battery. This makes sense to me, but also it means I have no clue what PA77 might refer to.
Bottom-line: I don’t know what PA77 is.
Samsung guarantees performance will be identical to the 25R, so I ran some discharge tests earlier to verify their statement as part of our supply-chain inspection process .
My testing environment is good and conditions here match Samsung's testing requirements of:
Actually we are exactly 30 degrees, the 1.5 degree extra is coming from the photo lamps.
Before the discharge tests I had to charge up the cells. Samsung stores the 25R at 50 ±5% charged state (from 3.640V to 3.710V). When I received them that was the case according to my Soshine charger - indicative of brand new cells.
The first two tests I ran are at a continuous discharge of 2.5A - which is our standard here for discharge tests as this is the upper limit of what a USB drive can provide for power, and we graph via USB for speed.
Very nice! The cell easily exceed manufacturer specs - being able to provide more capacity than rated, at a higher discharge current than tested for.
The third test is run to compare more closely manufacturer specs. The Samsung 25R is officially discharged at .2C or .50 amps to achieve its rated capacity. This is low, as most 25R use is maximizing its max. continuous discharge rating of 20A. But that is how all 18650 cells are rated for capacity, at a minimum viable drain. The more amps you draw, the less total capacity generally is available. This is called a loss of efficiency, and the efficiency lost from high-drain scenarios ranged between different chemical makeups.
Here is the Samsung 25R2 at .50A:
Take a look, it's interesting. At .50A the resolution of the discharge curve becomes more detailed. You can see three different peaks in voltage. Each one of these voltage peaks is accounted for by a chemical change inside the battery.
You may have noticed the capacity stayed the same, but the total energy increased.
How can this be?
By overlaying the graphs we can clearly see where the difference is:
A 0.10 volt difference between the discharges.
And this everybody, is exactly why capacity ratings can be misleading. Both discharges started, and ended at exactly the same time. They followed the same path, except the 0.50A discharge stayed 0.10V higher than the 2.5A-discharge. The same amps, for the same amount of time, albeit at a different voltage is in turn a higher total energy.
Analogy: Imagine a sink and a beaker. The beaker is very long and very thin - like an elongated pencil. You want to fill it up using the faucet. But every drop of water wasted is valuable energy lost. If you turn the sink on full-force you will fill up the beaker quickly, but water will splash and many drops will escape. So what do you do? You bring the faucet down to a drip, and you can actually catch all the water.
Most batteries do lose capacity when they are discharged with a higher current. The fact that the 25R5 loses no capacity between a .50A and 2.5A discharge is an excellent trait. Older battery chemistries (just a few years ago) were not this efficient.
The performance of the 25R5 is really outstanding.
A typical discharge test for a 25R2 (with same conditions as 25R5 test 1 & 2).
As Samsung SDI originally stated, the main difference between the blue Samsung 25R and the green Samsung 25R is the increased cycle life. A small capacity gain, or efficiency gain may be a side-effect of improved chemistry (the 25R5 has two years of research over the 25R2 so it's not so far-fetched).
Visual Inspection
The green Samsung 18650 25R we have have been talking about in all its glory. Let's go through a quick check list:
The diameter is 18.3mm, check.
The height is 64.9mm, check.
IMPORTANT: Digital calipers are recommended by Samsung for this test - but you must remember not to use metal calipers as they may short-circuit your cell.
I weighed both batteries, they are identical in weight which is very nice to see. Actually I fully charged one, and fully discharged the other because I wanted to see if there would be a weight difference. Just to be clear, I theorized no difference... and it does turn out the case is that there is no difference.
You may recall from the previous post about the Samsung 25R, that all Samsung top caps have three connection points.
I took the PVC off this one. These quality control markings can be seen through the PVC with a keen eye.
The most unique external characteristic of the 25R2 and the 25R5 are the etchings in bottom of the negative terminal of the battery. This battery has an 'H10', and I had to peel back the PVC somewhat to see it. No other 18650 battery series I've seen except the 25R has this (but that may be because I haven't seen enough).
Take a look at previous posts we did on the blue 25R2:
Is it a fake Samsung 18650 25R?
Awesome batteries - the Samsung 25R
Thanks for reading!
]]>SolarPlanet, the first solar-powered boat to circumnavigate the world.
In this blog post I look at 18650 batteries for electric boats, and take a closer look at the safe LiFePo4 battery chemistry which is gaining popularity for 18650 marine batteries.
There are two distinct uses for marine batteries:
The word ‘troll’ actually means to go round and round in repetition. The trolling motor is simply a system with an electric motor, propeller, and controls.
In fishing, trolling is when your cast one or more fishing lines with bait or lures. Often this is achieved by drawing the lines from behind a moving boat. This is not the same thing as trawling, which is using a net instead of lines. Open water fisherman often use trolling to catch big fish like kingfish.
A “trolling” motor is used to catch these game fish as a secondary means of propulsion to the main engine. Main engines don’t often operate as efficiently or quietly, or might need the extra help.
A trolling motor can also be used:
Trolling motor batteries have traditionally been lead acid. But lithium-ion for electric motors is becoming more popular and there are several reasons why.
LiFePO4 is a lithium-ion battery chemistry (particularly it makes up the cathode). LiFePO4 (lithium iron phosphate) is often acronymized down into three characters like other battery chemistries - in this case LFP (lithium ferrophosphate).
Google Trends
Google trends of popularity of "LiFePO4" search term. It looks like this battery has been popular since 2010, when PlanetSolar finished its circumnavigation; and the battery type has kept its popularity at the same level ever since.
Compared to lead-acid:
Chemistry |
Voltage |
Energy Density |
Working Temp. |
Cycle Life |
LiFePO4 |
3.2 V |
> 120 wh/kg |
-20 - 60 °C |
2000 |
Lead acid |
2.0 V |
> 35 wh/kg |
-20 - 40°C |
250 |
LFP is a naturally occurring mineral that is rich in iron. Its unique characteristics give the cathode a great thermal and chemical stability and make a safe battery. The drawback being that capacity is limited because lithium ions have a hard time moving through this material. As such, LFP particles are often coated in a conductive materials like carbon and have a lower capacity such as 1200mAh for a LFP 18650 (The LiFePO4 battery has also been made into a AA size "14500" that have a capacity of 600 mAh.). The anode is graphite or carbon as in most other 18650 batteries.
Lithium-ion is most notable for its exceptional and continually improving energy density. It is this reason that lithium-ion marine batteries are gaining in popularity above others.
LFP chemistry is particularly favorable because it has:
Other advantages of the LiFePO4 battery chemistry:
When a battery is overcharged, this excess energy has only one way out - it is converted to heat. Think about heat as the path of least resistance for the chain-reaction powering the lithium ions. The cell structure can no longer handle the load and play in the system it wants to, and volts can not be increased further. The energy only has one choice after the battery system breaks down, and that is to convert into heat. This is true of all batteries, and the LFP chemistry is no different. If they are overcharged enough, or mishandled in other ways (like being pierced by a nail) they still have the ability to heat up enough to ignite, smoke, or explode.
The bottom-line is the LFP chemistry is very stable, and does not react exactly like other lithium-ion cells. Heat generation is bad, but fire and explosions as an outcome is what everyone really wants to avoid. A fire is chemically a very specific process, where some substance combines with oxygen from the air. In LiFePO4 batteries, the bond is strong between the Fe (Iron), P(Phosphorus), and O(Oxygen) called the FE-P-O bond. This makes it much more difficult for oxygen atoms to be removed and cause an exothermic reaction.
The ‘Po’ at the end and ‘Li’ at the beginning creates a lot of confusion when distinguishing between these two battery types.
As you know, LiFePO is a chemistry. Li-po on the other hand stands for lithium polymer batteries. The polymer part refers to a soft, flexible material. Li-poly batteries are soft-pack lithium-ion batteries, like the ones found in drones, and mobile phones.
The LiFePO4 battery chemistry often finds its way into cylindrical 18650 batteries - with a hard steel case. They are then put together into a lithium pack with a BMS (Battery management system).
Li-poly is a term that only refers to the battery’s shape - a flexible polymer shell. A li-poly battery may be made out of a number of different battery chemistries.
Electric boats are a thing of the past, really. The first electric boat powered by batteries was in 1882. It was a seven meter long electric boat called the Electricity. Batteries were under passenger seats to maximize space for passengers. The boat ferried people around the River Thames and was very comfortable and accommodating. It could run for six hours at eight miles per hour.
They were not only quaint. There were some beasts in the water too. In the 1893 Chicago World Fair, electric boats carried over a million passengers. Luxury vessels could reach 70 feet long.
But by the 1920's the internal combustion engine started gaining dominance. Ship and boat engines had matured enough to harness the efficient use of combustion - which is still much more energy dense than batteries (kerosene has ten times the energy density of lithium ion). In 1920, William Oxford & Sons (the second largest shipyard in the UK) stopped making steam-powered ships and switched exclusively to Diesel engine. It was also the time Diesel powered engines were really commercialized, costs brought down substantially, and the first diesel car introduced.
Electric boats seem to have been forgotten except in some special cases. Most recently, solar power and lithium-ion batteries are giving them another chance.
Sail-boats can theoretically coast forever, circumnavigating the globe with wind alone. Solar boats have this potential too, which is very desirable for boating people. Sail-boats are at the mercy of the winds, while sunshine and energy storage in batteries have much more flexibility and less margin of error. Energy density will eventually decrease so that boats never have to stop running. Imagine giant shipping container boats that will not have to refuel. The largest shipping boats in the world produce more CO2 than all automobiles combined so there is also a dire environmental element to battery technology.
The Turanor PlanetSolar was the first boat to circumnavigate the world using only solar power and storage batteries in 2010. It has since been refitted as a commercial vessel, ferrying people around. It is all-in-all a good project. The founder stretched the limits of technology with this project, had a great adventure, and has turned it into something of a commercial success so it may live long,
Specs:
They fitted the ship with scientific equipment to measure and record currents, aerosols, and other natural phenomenon. One benefit of solar vessels is for research, where scientists do not want to disturb their environment with oil and gas.
These two partially-submerged hulls contain all of the lithium-ion batteries and the two electric motors. (Photo credit: Verge)
The crew can access the li-ion batteries from this waterproof encasement. (Photo credit: Verge)
The ship uses a 1.2 MWh battery with about 800 lithium-ion cells, each rated at a capacity of 500Ah. The total weight of the cells is a whopping 8.5 tons*. The cells were totally custom-built, by a company whose website no longer exists so it is difficult to find out their exact specifications (particularly their chemistry). Their use on PlanetSolar proves the usefulness of lithium-ion as an energy storage solution for vessels that use electric propulsion.
*Keep in mind the hull is built out of very light materials and the total weight of the ship is about 100 tons. That makes the marine batteries 8.5% the total weight of the ship.
A great view of the solar panels on-board this boat.
The top of the boat is fitted with around 130 photo-voltaic modules that cover about 500 square meters of the ship’s sun-facing surface.
Electric ferries have much more practicality than long-range “best of burden” ships. A ferry usually has calm waters and land very close-by. If it is too cloudy, the ferry can likely use the power-grid to charge while on either side of the route. Ferries on fresh-water bodies do not need to protect against corrosion, or a list of other hazards on the ocean - and thus can use cheaper batteries.
The Solar Shuttle is one such service in Europe, where there are a handful. This one connects Germany, Switzerland and Austria. It has the capacity to carry up to 60 passengers and obtains its energy, like you guessed, from solar cells on the roof. It has batteries under the passenger seats which carry energy if the day becomes cloudy. Keep in mind, this is almost the same design as the original Electricity from 1882 but looks much nicer.
Take a look at some of these pictures. The design is really nice and organic and is good to symbolize the environmental friendliness of the craft and the motifs behind their inception.
Photo Credit: Ippolito Fleitz Group
In many competitions, players are trying to get lighter. Energy density is the way to do that, and so for boat racing and boat tournaments the LiFePO4 battery is well suited. For example in bass master tournaments it can be critical to shed a few pounds of weight off your boat so you are able to get to the prime locations first.
This post was a small overview for LiFePO4 marine batteries. But there are other uses for this battery chemistry.
Solar power is particularly price sensitive and it takes a long time to repay investments in the field. The life-cycle of batteries is very important. Having to replace the batteries because their cycle life is too short can add years to a payback period that might already take 15 years. So a lithium-ion with a long cycle-life actually also translates to the li-ion battery with lowest overall cost, making LFP is very desirable for solar battery packs.
LiFePO4 batteries for electric vehicles are abundant. Electric cars, motorcycles, electric gold caddies, electric skateboards, and more all use lithium-ion (LiFePO4) batteries.
LiFePO4 batteries for laptops are also employed, most notably in the One Laptop per Child project. They use LFP batteries because they contain no toxic heavy materials (to comply with EU restrictions). The batteries are used in Gaza and the West Bank for community projects and in schools.
Other uses include:
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The original Formula E William’s battery needs to change, and some claim it is no longer desirable because of its high costs. The races have to be profitable and thus the price of batteries (one of the most expensive components in any electric vehicle) is being looked at very closely. The problem is that developing a completely new battery will cost millions or tens of millions of dollars and will take time as the whole industry must mature.
Possible rescheduling for a better battery
The battery competition section of the Formula E races is under consideration to be delayed until 2018 or 2019. The reasoning follows, as the old battery is not good enough to really kick-start the concept. The new battery needs to be a whole new generation of cell, one that can deliver more power and for a longer time.
The next evolution can’t just be good, it has to be a leap ahead of the current tech. The proposal to delay the match until a better battery is decided will have to be agreed on by all teams.
Formula E Williams electric car battery
Williams Advanced Engineering has been closely aligned with racing for decades and produces more parts for the F1 cars than any other group. They are now manufacturing the batteries for the FIA Formula E championship. They will have to deliver cutting-edge lithium-ion batteries to forty vehicles, with very tight restrictions, all in record time.
Technical highlights (Mandated by the FIA and Spark Racing Tech.)
As well the electric car battery has these constraints
Key technical challenges
Soichiro Honda
I’m not sure who said this first, but it is often attributed to Soichiro Honda, the Japanese engineer that started Honda more than half a century ago. What does this adage mean and what does it have to do with Formula E? The notion here is that by selecting for the best, and by using competition to make it better, the improvements incurred will drip down into the whole system.
So racing and the Formula E is not just exciting to watch as a bystander. It’s also an important part of the evolutive system that electric cars are part of of. Racing is, and always will be pushing at the boundaries of knowledge and technology.
KERS
This was evident when the Formula 1 started using KERS or the Kinetic Energy Recovery System. It recovers kinetic energy that would otherwise be lost as heat to the automobile through the braking system. The newer ERS system uses two motor generator units, an energy store, and control electronics.
The first motor generator is called the MGU-K, which converts kinetic energy under braking into electricity. The energy goes into the “Energy Store” which is comprised of lithium-ion batteries. The second motor generator called the MGU-H, centers around heat, specifically the heat created by gases in the exhaust. The heat is converted into electricity and also stored in the same li-ion batteries.
The Team behind the Formula E battery believe electric car batteries need to improve these characteristics the most:
The BD is grey and the BE is green
The Panasonic NCR series is perhaps the most important line of lithium-ion batteries. If that is too far a stretch because you prefer li-poly which is also good, no one would argue that they are at least big-shots of the 18650 world. The NCR18650A was the first really high-capacity lithium-ion battery in the marketplace, which is the key metric driving demand of electric vehicles - the largest market for these type of cells. The NCR18650B which came some time later is the NCR18650A's usurper with an even higher capacity. These are the two commodity cells which mostly define the "energy density metric" which all energy analysts follow so closely.
The Panasonic 18650 B is the battery powering the current generation of Tesla Model S and as such receives good attention.
The Panasonic 18650 B has cousins. They are slight variations to the original chemistry that produce slight variations in end performance. Electrolyte balances are slightly tweaked, or other changes are made to the original chemistry such that variables like cycle life, or capacity can be honed in and maximized. The Panasonic B is no exception, especially with its popularity, so it receives many variations. One variation may one day lead to the next generation of battery with a substantially (+200 mAh) higher capacity.
In this blog post I will compare the specifications and visual characteristics of two popular variations of the NCR18650B - the NCR18650BD (grey) and NCR18650BE (green). I will first post the original manufacturers specifications and then put them in a table for easy comparison. I'll walk through each spec, and finally take some pictures so you can identify the battery and its parts.
Panasonic 18650 BD | Panasonic 18650 BE | |
Rated Capacity (mAh) | 3000 (at 20°C) | 3200 (at 20°C) |
Min. Nominal Capacity (mAh) | 3080 (at 25°C) | 3030 (at 25°C) |
Typ Nominal Capacity (mAh) | 3180 (at 25°C) | 3180 (at 25°C) |
Discharge current for ratings (A) | 0.61 | 0.61 |
Nom. Voltage (V) | 3.6 | 3.6 |
Charging Voltage (V) | 4.2 | 4.2 |
Charging Current (A) | 0.9 | [Fixed] 0.909 |
Charging Time (hours) | 8 | 5 |
Max. Continuous Discharge (A) | 10 | 3.63 |
Discharge End Voltage (V) | 2.5 | 2.5 |
Max. Weight (g) | 49 | 48.5 |
Max. Diameter (mm) | 18.5 | 18.2 |
Max. Length (mm) | 65.3 | 65.5 |
Max. Temperature (°C) | 70 | ? |
Rated capacity, nominal capacity, nameplate capacity, or maximum effect - in many industries - all share the same meaning. That is the intended full-load sustained output. For lithium ion batteries the definitions are actual separate. Rated capacity and nominal capacity are often written as two distinct variables on a spec sheet, one followed by the other.
The United Nations Manual of Tests and Criteria define Rated Capacity as the capacity, in ampere-hours, of a cell or battery as measured by subjecting it to:
For lithium-ion batteries, nominal values are used for factors with variability to distinguish them from real or actual values. For example, 18650 battery manufacturers have levels of tolerance for the capacity of their batteries. It is impossible to refine the materials and processes so exacting as to produce 18650 batteries with capacities within a single milliamp hour. That is why even within Grade A 18650 cells are Ranks A and B, the latter with a capacity 10-30 mAh less (in application this difference usually only matters when putting cells in a series).
This variability in battery capacity makes it impossible for the manufacturer to approximate a single real value. Instead they use a nominal capacity (one with a certain tolerance) and usually divide this factor further by a minimum and a typical rating so you can appreciate the range of capacity this cell might have in reality when you receive it.
I am referring to a United Nations regulation from 2010 which found that rated capacity was not adequate to rate a lithium-ion battery. The determining factors going into the rating can too easily be exaggerated by manufacturers to gain an unfair advantage by claiming capacity higher than they should.
If you are in the European Union, this is not the case. The EU uses International Standard (IEC 61960) as a globally recognized standard to evaluate the rating of a battery. The EU does not require a watt-hours label.
The new regulations state that battery manufacturers must include Watt-hours. So when you are determining which cell and which capacity will fit your application, take some time to look at watt-hour rather than only a rated capacity it your capacity demands are stringent.
The United Nations Model Regulations are such:
"Watt-hour"
"Rated Capacity"
Differences
So which battery has a higher capacity? Well, with such ambiguous definitions, it is quite difficult to say out-right. My instinct after reading the United Nations report on the definition of rated capacity is to go with the more variable nominal rating, especially its typical designation. In this case both the 18650 BD and the 18650 BE have exactly the same typical nominal capacity of 3180 mAh.
With every battery discharge test you run at home, you also have to consider the three factors (load, temperature, voltage cut-off point) if you want to get your own battery specs to match with the manufacturer's. You can see the proper conditions in the comparative spec chart posted above.
The characteristics of the discharge test for both batteries are:
To find out more accurately in my own case, with two battery samples, one BD and one BE which has a higher capacity I used an 18650 charger and custom-built Arduino lithium-ion battery discharger with an 18650 adapter and a port through USB where I can chart the discharge curve.
I always like to run through three to five discharge cycles before using the data from the discharge curve for analysis. I find that some cells do not need the initial cycles, but others do. It depends on what tests the manufacturer performed on them, how they were stored, and how long they were stored. It also depends on their chemistry type and how they particularly handle the transfer of ions. To have a more accurate test it's good to cycle them a few times, seeing that they charge up to their full capacity.
Discharge tests should start with a fully charged battery at 4.20 V but with my set-up and in application my tests start at ~4.16 V. This quick volt drop in the beginning is just a millisecond and does not account for a notable change in the ending capacity. Also make sure the end-voltage is correct as some unaccounted volts at the end of the curve can easily account for 100 or 200 mAh. Every battery is rated differently and in this case of the BD and BE the discharge tests should end when the batteries are at 2.5 V.
BD Capacity (mAh) | BD Energy (Wh) | BE Capacity (mAh) | BE Energy (Wh) | |
Test 1 | 3136 | 10.59 | 3115 | 10.5 |
Test 2 | 3114 (-0.70% change) | 10.52 | 3101 (-0.40% change) | 10.47 |
Test 3 | 3061 (-1.70% change) | 10.34 | 3099 (-.006% change) | 10.46 |
Average | 3103 | 10.48333333 | 3115 | 10.47666667 |
Capacity difference (mAh) | 12 | |||
Energy difference (Wh) | 0.01 |
Here is the data from the above tests in an easy format to compare. I wanted to know which cell had a higher capacity - but there is no winner. The Panasonic 18650 BE has a higher capacity but only of 12 amps (about 0.3% of the total capacity), which is well within the margin of variability. From these discharge tests I would conclude the BD and BE both have the same capacity, and my numbers line up very well with what I would have expected by following the manufacturers nominal capacity rating.
Remember the typical nominal capacity for both batteries as outlined by the spec sheet is 3180 mAh and had I limited my amp drain from 2.5 V down to .61 V as per testing conditions for the spec sheet I would have easily hit this capacity target.
This goes very much against the rated capacities of each battery. The BE is rated at 3200 mAh while the BD only 3000 mAh. However under closer look, both batteries share exactly the same capacity rating.
Most aspects of these two batteries are the same. However charging time and maximum continuous discharge ratings are very different. In a higher-drain situation you must choose the BD over the BE. The BE has a very low drain limit (about 3 amps) compared to the BD (with about 10 amps). If you need acceleration, torque, or burst power of high amps - there is no contest, the BD wins.
Interestingly enough, for the 18650 BD to achieve this it had to be compensated for with a longer charge time. The BD takes eight full hours to charge on its rated charge current of .9 amps. The spec sheet states 3 amps is the limit this battery will take. Compare that to the BE with a reasonable five hour recharge. That is actually a 40% decrease in charge time.
So you must weight amp discharge with charge-time if you are choosing between these two batteries, as all other specs are more or less the same.
The appearance of your battery
Should not have
You should also take a look at the pictures below and see that they match your own batteries.
Profile Shots
Compare your batteries to these shots. How similar are they? The color in my BE shots is really off because of the blue background yellow lighting. They are a lime green and not so yellow in real-life.
QC Code under PVC
Here is something you can quickly check for. The Panasonic BD and BE both have a quality control code printed directly on the steel underneath the heat-shrink PVC. However you can still see it, albeit faintly. Check to make sure your cell also has a code somewhere visible. Other markings may also be visible, for example my BD had an alphanumeric near the negative terminal as well. If your battery is missing all QC codes it is a red-flag.
Top-cap comparison
Panasonic has the most variety of its top caps in 18650 batteries. The grey BD has a circular positive terminal very similar to that of the Samsung 25R. It has three connection points between the positive terminal and the rest of the top cap.
The Panasonic 18650 BE on the other hand has a sharp, triangular positive terminal.
Here you can see the two batteries and their positive terminals side-by-side.
Negative Terminal
The Panasonic BE is also unique because of its bottom terminal with an indented ridge.
Length Measurement
IMPORTANT! Never measure your battery like this using metal calipers. You always want to be extra careful not to connect the positive and negative terminals as this will short-circuit your battery and potentially cause an explosion.
All the measurements check out to the spec. sheet max values and actual values do not exceed what was expected.
Weight Measurement
The BE weighs in slightly heavier than the BD.
If you are building rechargeable battery packs, Panasonic cautions the following on design:
Designing a lithium battery back
The protection circuit for the battery pack requires:
Avoid connecting cells together by soldering. Many DIYers weld directly on the top-cap of the batteries which can (pretty easily) lead to short-circuiting. As the negative and positive terminal meet right near the top of the battery, a bit of solder which slides to the edge of the battery is all it takes for a thermal runaway event.
The proper way to connect batteries is with lead plates and spot welding.
*Water ingress is the leaking of water into an enclosure.
You should store the batteries under the following conditions:
If you are storing them longer than three months the only difference is
The Panasonic 18650 BD is shipped out at 48% charge which is just about 1500mAh. Every month the batteries are stored, they will lose some voltage. This is why when you receive the batteries they will have a slightly lower charge.
The BD should has a lower limit of 2.0V - so consider discharging your batteries but monitoring that they do not go under 2.0V. Maintenance every few months might be necessary to top up capacity. Cells under 2.0V will start to decompose.
]]>A new semi-electric rocket engine named Electron with the new Rutherford engine is being developed by Rocket Lab - a Lockheed Martin-funded rocket startup. Their edge is purported to be 3D-printed parts and their use of lithium-ion batteries. The 3D-printer allows a faster iteration for the engineering team (which is also a core edge SpaceX has over NASA). The batteries are used, not as the main fuel source (which may never be possible for rockets), but as the power for its turbopump.
The turbopump is used to pressurize the liquid propellent and then feed it into the combustion chamber part of the engine. Traditionally, gas or liquid fueled turbopumps have been used in rockets since the 40’s and are used in things like the Ramjet motor too. The extremely high pressure (50 psi -> 1400 psi) the Rutherford engine’s turbopump creates is required for the force to propel the rocket and payloads into orbit. These pressure extremes put the turbopump under such stress and heat (up to 760°C) that it glows bright continuous red.
The Rutherford engine
This red glow is indicative of two major difficulties when pushing the limits of the turbopump. That is mechanical strength (which is roughly equal for electric and traditional pumps) and heat dissipation. Electric turbopumps have been claimed more efficient on the basis of far less heat dissipation - but it seems not the case with the Electron rocket as their turbopump is indeed pushed to its limits.
Battery-power translates to a smaller turbopump - just the size of a soda can. It doesn’t need to be attached with tubes and pipes to the rest of the engine; it doesn’t share any fuel. It is a 3D-printer electric motor powered by batteries.
Other specifications
Electric circuitry on-board the Electron rocket
Batteries maintain their weight when they are completely discharged. As fuel is used on a rocket, it becomes lighter. Empty cells are still very heavy.
The engineering behind a rocket turbopump is the most complicated aspect of a liquid-fueled engine. Replacing it with a simpler battery powered solution does not address the fundamental problem which is the power-to-weight ratio. Electric motors do not come close to the horse power per pound of a propellant-powered turbopump.
So far, it seems batteries won’t matter much. The energy density and weight of the batteries for a rocket do not necessarily justify the switch. The fuel for the main engines can be used to power the turbopump instead as it is done traditionally. The new SpaceX Falcon 9’s payloads are about ten times cheaper and the turbopump does not use batteries. However the Electron is purported to be a tenth the price of conventional boosters.
What is true, is that using batteries for rocketry would probably not have been possible just ten years ago. The energy density was too poor and the added weight simply too much. But will they catch up anytime soon? There are very large challenges ahead, so we will just have to wait and see.
Any advancement is energy storage, rocketry, and lithium-ion batteries is interesting. Rocket Lab intends to lower the cost of launching communications satellites into orbit. Everything they are doing and planning on is great, and Battery Bro wishes them much success.
Solar Impulse is one of the most interesting projects anywhere in the world. It is a fully-solar powered plane, that one day in the future will never have to stop flying. During daytime, the wings which are covered in solar panels charge the plane’s lithium-ion batteries. There are four engines (two on each wing) with a propeller and inside each engine housing, high-capacity lithium-ion polymer (soft-pack) batteries covered in a protective and proprietary foam.
The plane is now standing by in Nanjing, China, gearing up for leg 7 of 12 - where it will take flight across the Pacific to Hawaii. The adventure will take six days and six nights and will be piloted by André Borschberg. Go over to their website and follow the flight in real-time.
You definitely don’t want to miss Solar Impulse’s journey, it is simply incredible. Their prototype electric aircraft broke eight world records. It was the first plane with lithium-ion batteries to fly through the night, between continents, and across the US. The current leg of the journey is completing a full circumnavigation - an around-the-world flight.
General characteristics
Performance
Lightness
The carbon fiber plane has a 72 meter wingspan, which is roughly equal to that of a Boeing 747. This plane is really a gentle giant, and shares ideals with the albatross - a bird that soars across oceans with a massive wingspan. And despite the large size, the skeleton is light and the total weight is less than a Volt electric car.
Solar panels cover the wings - 17,248 to be exact. This is enough power to fully charge the batteries in about six hours, and allow the four electric motors (17.5 CV each) to stay airborne all night.
Inside the lumbering giant is a small, hollow room with a few monitors a controller and space enough for one person. Piloting the first solar-powered plane to fly around the world is no easy task. The Solar Impulse 2 has capabilities to allow a pilot to live for one week without landing.
The cabin is not pressurized like normal passenger planes are - that means the pilot needs to wear an oxygen mask. Weather conditions vary from -40°C to +40°C so the pilot must also wear protective clothing. Every morning, the pilot climbs to 28,000 feets to harness the most sunlight, and at night descends to 3,000 feet to conserve energy. Actually the descent is a use of potential energy created by height gained during the day to help the plane get through the night.
Food is being developed by Nestle, and is making meals and snacks that can withstand extreme temperatures. Going to the bathroom is surprisingly simple - and unlike in the International Space Station, gravity does most of the work for the pilots of the Solar Impulse.
Pilot of Solar Impulse in cockpit
Whoever is piloting the craft will also have to adapt to polyphasic sleep cycles, where instead of sleeping once per day (monophasic) or twice per day (biphasic), a person sleeps many times a day. Pilots of Solar Impulse sleep in short 20-minute spurts. Some people have been on this sleep schedule for years, and it is used by the military and NASA. After waking they will often stretch, meditate, or do yoga to exercise the body and mind.
"If you work eight hours in front of a computer, you are in terrible shape. It’s the same here — if you fly all the time, you end up in terrible shape, so we need to find ways to get rid of these strains that you have on the body." Said Piccard.
Energy storage represents is the plane’s primary inefficiency, but also is a very achievable goal to improve upon. Piccard has this to say on the state of battery technology for aircraft:
"The batteries we have used have been specially developed for optimal maintenance but are still 10 times heavier than kerosene. I would imagine that we are still 20 years away from attaining parity on this point.”
Motors output 8 hp (6 kW) during a full day and night cycle, which is roughly the amount of power in the Wright brother’s plane. This major constraint by the batteries puts the aircraft just on the edge of flight, with no margin for error.
This solar-powered aircraft Solar Impulse uses four main lithium-ion batteries, each containing 70 lithium-polymer cells. It does not use a commodity cell like the 18650 that Tesla uses. There are several reasons, foremost being weight. An 18650 battery is in a steel housing, and a lithium-ion polymer battery like what is in this aircraft or in a cell-phone is housed in a soft, thin, flexible material. That is why nearly all drones, RVs, and electric planes use polymer (soft-packs). The polymer pack used by Solar Impulse is completely custom-built.
Particular concerns for lithium-polymer batteries fit for airplanes:
Things that need the most work:
The batteries for the Solar Impulse were produced by the Korean manufacturer named Kokam. The special chemical formula improves the cell’s oxidation issue. The analogy that Solar Impulse use is “Just as an apple gets dark and rots when peeled and left outside, batteries age faster and lose efficiency when oxidized.”
They claim the technology is two years ahead of the industry which is realistic as large Asian manufacturers like Panasonic or Samsung which dominate the market are much slower to change. Perhaps smaller battery manufacturers outside of Asia are on-trend as the market competes to adapt to high-demand and quickly changing battery technologies.
More battery specs
As was said earlier about extreme temperatures that pilots must endure, the li-ion batteries on electric airplanes have the same issue. Efficiency loss is very troublesome when flying through the night. If many of the batteries underperform and battery capacity is compromised - the pilot would have no choice but to use his parachute, survival training, and bail from the plane.
To maintain optimal temperatures, they treat their batteries like NASA does and heat them. Scientists found that the optimal temperature for their batteries was a constant 25°C. This temperature is maintained throughout the entire motor gondola with a heating system. The efficiency from running lithium-ion at their proper temperature is critical to keeping the craft airborne all night.
Like with all other aspects of this plane, there is little margin for error when charging the batteries.
The plane can reach a speed of 100 mph, but the optimal speed to get the most distance out of the batteries is around 60 mph.
Monoflourethylencorbonat solvent was added to the crafts lithium-ion batteries. It is developed by Solvay Chemicals, and depending on blend can account for up to 20% of the batteries’ total electrolytes. The main advantage of their blend was a higher energy density.
The insulation foam that cover the batteries were developed by Bayer Material Science. It has thin pores, high rigidity, and good strength, all while being extremely light.
The lithium-ion polymer batteries are all independent of each other. A balancing controller is in place to insure power between cells can be transferred in the case a motor fails. And each battery is fed to a particular solar panel which corresponds to a certain motor.
Volt Air electric aircraft concept
Picard said the following about the broader significance of such a project:
"It’s really to show what we can do with renewable energies, and with key technologies that can save energy. This is really the vision I had in the beginning, to do something extremely difficult, something that people would consider impossible."
Others, such as Tesla’s Elon Musk have said that the first fully-electric passenger plane that could cross from California to New York will be available in around twenty years.
If predictions of trends are correct and battery energy will be on parity with combustible fuels in twenty years - will aircraft actually become electric? The foremost metric is “Cost per kilowatt hour” which continues to steadily decrease year by year, and has very achievable goals ahead of it to improve. It may even be decreasing at an exponential rate.
It might be that one battery break-through immediately makes electric planes accessible. Until then, it seems it will be a slow, adventurous journey. The margin for error will grow as energy density rises, and items of comfort and more passengers will be added to the planes. And if battery technology continues as it is doing now, within twenty years, the future generations of Solar Impulse will help define parts of our sky.
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Quickly knowing whether a battery is counterfeit is possible, here I'll show you how by taking a look at the Samsung 25R.
I picked the Samsung 25R because of its stellar reputation as a great high-amp cell. It finds use in electric cars, power-tools, vaporizers, and more and will almost certainly continue as one of the most popular 18650s at least until late 2015 when a newer generations could gain traction.
You might ask "Are the 25Rs even faked?" It was once thought unlikely because of their availability.
News Story: Houston woman gets a year for selling fake Samsung batteries
(April 2015) A 53 year old Mexican woman named Graciella Balderrama in Houston pleaded guilty and was sentenced to a year in prison for selling counterfeit Samsung batteries on Ebay. She’ll almost certainly be deported after her time in prison and has to pay $90,000 in restitution to Samsung SDI.
The court heard from a Samsung representative who clarified that Samsung takes pride in creating quality products. He noted that Samsung is very concerned anytime counterfeit goods, in breach of its own logo, are introduced to America. Of special concern is when these counterfeit products present a public safety threat like counterfeit lithium-ion batteries do.
And Balderrama participated in a conspiracy. Police have messages of her talking with her contact in China, where she acknowledges understanding the batteries were not genuine but consented to continue working.
Balderrama confessed to authorities she understood the batteries are not genuine Samsung batteries, but she continued to package and offer them as legitimate. Counterfeit lithium-ion batteries really are a public security concern since they cannot follow security regulations. Fake batteries can be dangerous and even explode. This is particularly a growing issue in China where the batteries are created.
Reported here.
So how likely is it that there are fake Samsung batteries on the market? Very likely indeed. Therefore it is vitally important consumers and suppliers are able to tell the difference.
Here are the official 25R specifications for your reference:
The first, easiest thing you can do is a visual inspection. Look at key features of your batteries and compare them to pictures on this blog post. For this blog post I used two 25R cells for each section so we can take a look at the differences between cells. They were bought from two different suppliers.
Here are two Samsung 25Rs side-by-side. Do your cells have any noticeable differences? Variations that are safe include slightly different hue for blue than picture (because of different lighting conditions), placement of any printed components (can be offset in both x and y planes). For example the text printed on the PVC is never aligned with the text printed below on the steel.
You may have noticed the text is actually made up of small circles. Counterfeiters may not take care to have exactly the same font and number of circles so sometimes I will count the top-most row of the text's circles and see if they match. It takes about 20 seconds to count, so for your reference, a genuine 25R has the following number of circles in its top row: [I:3, N:2, R:4, 1:1, 8:3, 6:2, 5:5, 0:3, 2:3, 5:5, R:4].
You should be able to see some kind of printed text on the steel under the blue PVC cover. If you look hard you can see an 'E3C4' in the center of the left battery in the image above. The right battery also has a code - see if you can find it. If your battery at home has no faded code underneath the PVC it is likely fake as I have never come across a 25R without them.
Take a close look at your top-caps (positive terminals) and the white washer - there should be no variation between this photo and your battery when looking at the top cap. Important: The Samsung 25R has a very circular positive terminal with three points of connection.
Take a look at the negative terminal of the battery. This is a normal amount of wear on a brand new battery, as the machines which move and test the batteries in the factory often leave scratch marks like these in the center. Beware of unusual amounts of wear and tear.
Make sure that the metal seen is a "silvery" steel color and not "golden" copper. Copper is used as the conductor for nearly all printed circuit boards, including those employed on protected batteries often found with flashlights. If you have a copper negative terminal you also likely have a protected battery that a 3rd party supplier added. You can confirm this by measuring the height of the battery - a protective board can add around 15 mm.
Keeping these contacts clean with a microfiber cloth will help prevent arching.
Besides copper negative terminals, you will also find outdented bottoms on re-wrapped batteries like this Ultrafire with an unknown metal. Original 18650 batteries do not have any protrusion and the 25R is completely flat.
Simple DIY Measurements
For these measurements, you will need some rudimentary tools, like digital calipers and a jewelry scale. So feel free to pass over this section if you don't have these things at your disposal.
Digital calipers are a cheap way to add an extra bit of evidence when determining authenticity of cells. Manufacturers release data that can be used to confirm authenticity - like the nominal specifications posted above. Width is not the most telling factor, as there is little variation in 18mm 65mm (18650) batteries. However, it takes a small moment so I'll have a quick check.
IMPORTANT: Do not use metal calipers without putting some electrical tape or other insulator over the ends. I don't use metal-tipped calipers. If you connect the positive terminal and negative terminal with anything that conducts, you can short-circuit your battery.
The width should be between 18.26 mm and 18.40 mm. My calipers only have an accuracy of .20 mm, the measurement I took was 18.20 mm, so the actual width of my battery matches the nominal size in the manufacturer's specifications.
Checking out the length, there is more variation here between different batteries. My measurement comes out to 65.30 mm, with a .20 mm error. Nominal specifications require 64.85 mm with a 0.15 mm error. The total error is .35, so my measurement actually falls short by .10 mm even accounting for the error. After realizing this I went back and took the measurements again and made sure to zero the calipers. My actual length measurements now match the nominal manufacturer specifications and everything is fine.
I put a dot on the battery so I don't mix them up. This is what the first battery weights in at - 43.63 grams.The nominal specs say the 25R should be 45.0g max and nothing else. So the first cell checks out fine.
Here is the weight of the second battery, with nearly no variation from the first it also checks out fine at less than than maximum 45.0g allowed.
Getting naked, taking off the PVC heat-shrink
Markings part one. These markings "J5E8, 48332" and "J5E9, 498B2" can be found one one side of the battery near the top-cap.
When I spin the batteries around I get more markings. Written here is "E3C4" and "IED6, IED6".
Now I don't expect your Samsung 25R batteries to match exactly, but if they have these two types of markings on either side it is a nice piece of evidence to add that your batteries are genuine and not fake. I am not sure why the right battery has its code printed twice or that it appears to be darker, but these two factors play no role in determining authenticity apparantly (as each cell was later tested and confirmed to be genuine).
This is the vent of your battery - it spews bad stuff when the battery overheats to relieve pressure. Something mildly interesting about the Samsung 25R is that is has quality control markings right next to the vent, and most batteries do not. Pictured above is a good viewing angle to check out your battery's vent.
If you get the lighting and angle just right you can actually see the etching marked into the 25R battery near its vent. The other 25R also had a one letter + one number combination. A magnifying glass makes this much easier to do and it can be challenging to find the code especially without removing the white washer and PVC.
I looked at other cells from various manufacturers like the LG HE2 to see if they also have markings near the vent. They do not, and my small search indicates it might be a unique marking to the 25R. So this is a fairly straightforward way to verify your battery as a 25R.
Here is a better look at the battery top-caps with their PVC and washer removed. Aren't they pretty?
Now this is an interesting feature! Both Samsung 25Rs that I'm testing, once the PVC is removed, are revealed to have a tiny '0' marked into them. As none of the other 18650's I've tested have this marker - it may be an excellent way to quickly identify a genuine 25R from a fake.
A closer look at the symbol, with some "enhancement" so you don't have to squint. The cross through the circle designates a zero. I do not know if all Samsung 25R cells have this mark, but the two that I tested for this blog post do. You will have to peel back the PVC on the bottom-rim of your battery to do this test. While there is likely little danger in doing this - it is best to completely replace your battery wrap with a new heat-shrink tube afterwards.
I am interested to hear if others also have this 0 marked into the rim of their negative terminal. If you do, please send us a picture or a comment and I'll attach it to this blog post.
I needed to check that other brands of batteries and other Samsung batteries do not also have this zero etched into them. They do not, and it seems to be a unique characteristic of the Samsung 25R.
Stickers on your battery?
Note that many lithium-ion batteries have a separate sticker on each cell which states the cell’s size, voltage, and capacity. International shipping rules mandated by the United Nations require this information for each cell when shipped via air freight (note: this is not necessary for sea shipping.) Suppliers will print batteries or tape a piece of paper with this information and stick it to the battery. It does not mean the batteries are fake, just that they were shipped via air freight from Asia and the suppliers needed a simple way to comply with the rules.
Here is an example of a couple 25Rs with shipping stickers on them. I found this image on Ebay; you can deduce that the supplier had them shipped via a cargo plane (because ships don't require the stickers). You can also deduce the supplier bought less than 10,000 cells as this is around the number where shipping by sea becomes necessary.
Top-cap Identification (Top-cap ID Method)
You may have never noticed, but each brand of 18650 has their own specific top-cap which is very difficult to counterfeit. A counterfeiter would need a very cheap way to completely take the battery apart, and put it together again with a low (undetectable) amount of damage. In my experience, this just doesn't happen and is too difficult. Therefor it is possible to ID an 18650's manufacturer just by glancing at its top cap.
The lithium-ion battery manufacturers like Samsung, Panasonic, LG, patent absolutely every new idea they have. Licensing technology like the NCR chemistry or other parts of a battery is very profitable so intellectual property protection is important.
It is for this case I suspect each brand of battery has their own particular style of top cap. I do not believe there is any real advantage to any of the designs, and a consumer will never notice a difference. That is, unless they’d like to identify the battery’s brand.
I took about ten batteries of each brand and put them all together in groups to see if I could notice a difference. The difference was obvious immediately, and held up for each group of batteries. So this is a very quick and easy method to see which brand a battery is.
View this image larger on Imgur: http://imgur.com/4gnFl7m
Cells made by LG Chem have four connection points between the positive terminal and body of the top cap. Samsung cells have three. Panasonic cells have more variation and both triangles and three-point contacts were found. As well, many suppliers re-wrap these cells and add a button-top which is seen last. There is also variation in shape of the positive terminal excluding the connection points between being round, straight, or a combination of both.
Maybe you noticed the Samsung and one variation of Panasonic positive terminal were very similar compared to the others. Can you tell the difference between them in the picture above? The correct answer is that the right battery is the Samsung. Check out the small differences, the most notable probably being the dark ring around the circumference of the Panasonic, where the Samsung does not appear to have any such ring. The Panasonic also seems to have a flatter surface near its vent.
Difference between washers
Washers are probably not something you are very interested in. But it adds another piece of reliable evidence to the authentication process. Counterfeiters have a very difficult time being so thorough so it is our edge to have a more complete picture than them.
It is probably true, because of patents, that the washers between manufacturers are also different. I've taken an LG HE2 and Samsung 25R washer for comparison above. With the naked eye and discernment of my fingers it was much easier to distinguish differences... the photo does not do a great job at showing the differences.
The left washer is the Samsung 25R - it is brighter, more brittle, and smoother with a glossy finished surface. The LG HE2 washer is slightly browner, without a glossy finish, and is much more elastic and less brittle. The 25R will resist well against bending, and the LG HE2's washer bends easily like paper. The 25R washer can be pulled apart and snapped quite easily, while the LG washer stretches and is harder to snap apart.
There might be advantages to different washers at high-heat and how they react and help stop thermal-runaway events. But I think that's really a stretch and likely one does not have any benefit over another. However it is another indicator of authenticity that can be corroborated with the others.
Let's just measure them before moving on. The hole is about 9 mm in diameter. The 25R's ring is .30 mm thicker than the LG HE2's.
Taking a look at batteries under a blacklight
Black lights are pretty cheap and small key-chain lights for identifying fake currency are easy to buy. So half-way while writing this blog post I realized the opportunity and took a walk and bought one. Let’s see if there are any peculiarities while putting a line-up of 18650 batteries under the black light.
Note: The 25R wrapper is not on tightly, as I took this picture after I had already deconstructed the battery somewhat.
The 25R glows brightly when under blacklight, at about the same level of intensity as the other two Samsung batteries. From this I may conclude that Samsung batteries show brightly under blacklight. I can not say exactly how bright without equipment I do not have - but I can compare them to some fake VTC series batteries I was sent as samples from a Chinese supplier. What is interesting is that the fake batteries show a much less saturated reflection of the blacklight, indicating a difference in the chemical composition of the PVC.
If you have a little blacklight key-chain you can check your Samsung 25R PVC. It should be fairly bright, if it gets darker under blacklight it is indicative of a counterfeit cell.
Defects and visual signs of wear and tear
Here are some other ways you can quickly see whether your battery is new or used. There are some obvious defects that a manufacturer would never allow to be sold off to a reputable dealer. If your “new” batteries show any of these signs of wear and tear you have likely purchased used batteries.
The Burn Mark. This battery came with a burn mark that must have been very hot to both scorch the steel and burn away the plastic washer. It was being sold as a new VTC5 but is certainly not. This battery should be recycled.
The rust spots. What is rust doing on your batteries? This is bad news and indicative of a really old battery. Again, this cell was being sold as a new VTC5. If your battery is rusting like this when you buy it, it should be put directly in a nearby recycling bin.
Large amount of bottom scratches. This photo did not do the scratches justice. The entire negative cell was very scratched, in many direction and with scratches reaching the rim of the battery. This is far more damage than the regular wear and tear from a manufacturer's assembly line. This battery was also being sold as a new Sony VTC5 - but is obviously not.
Samsung 25R discharge tests and voltage noise
Ok so discharge tests are not easy, or quick at all to do and is an exception to the title of this blog post. However I wanted to show you discharge tests quickly to show you what a good clean discharge looks like, and what a dirty discharge looks like. First I charge each battery up to 4.2V with this charger. You can see over 2500 mAh is now held by the battery.
I then use this custom Arduino battery discharge with an 18650 adapter. I have taken countless Samsung 25R discharge tests. I have recorded all kinds of discharge curves and want to give you a quick sense of the curve so you may appreciate voltage symptoms in low-quality or counterfeit 25Rs.
This is what a normal, brand new cell's discharge looks like. It is not as flat as a high-capacity cell but it is a very flat curve (lithium-ion) for batteries nonetheless.
This is the discharge curve from a Samsung 25R too, but notice the two small blips in voltage. This is indicative of a lower quality cell.
The third is the worst. And this is also the curve of a 25R, albeit with large amount of noise and excessive voltage swings. These voltage dips also caused the final capacity to drop by 100 mAh compared to other tests. If you notice a lot of voltage jumping your battery may be discharging in a similar way.
Identifying fake batteries (like the Samsung 25R) quickly and easily
As this post is so large, it only makes sense to break it down with some take-away points if you skipped all the details:
Thanks for reading! Any questions or comments please let me know below.
]]>New tests performed by a United Nations effort called the International Civil Aviation Organization have just confirmed that the fire-suppression systems onboard airlines do not have the ability to stop thermal-runaway events in the case lithium-ion batteries catch on fire.
The authorities are now scrambling to come up with a new way to package the batteries that would prevent these issues. Until a solution is found, analysts predict more airlines will ban the batteries from ever boarding flights, and in October a bulk ban will be offered, and probably eventually be approved.
An interesting test was performed by the FAA in February of this year inside of a pressurized cabin. The main gas used by fire suppression systems on board flights today is called Halon. The systems are triggered by smoke and continually pump out Halon gas into the cabin until five percent of all air in the cabin is this gas. In the test, the batteries actually exploded, causing the pressure to increase from the average of 15 PSI to 70 PSI quickly - which could be catastrophic for the structural integrity of an airplane.
It has always been the case that the FAA’s stance is that a high concentration of Halon can put out any fire, including those started by lithium-ion batteries. However that is no longer the case, and the opinion has been shown as fallacious. In March, the International Coordination Council of Aerospace released a paper about bulk battery shipments which labeled them as an unacceptable risk.
What is interesting to note, is that on the top ten list of most dangerous goods - lithium ion batteries rank number one, ahead of ammunition and fireworks. Lithium ion fires are extremely difficult to extinguish - carrying the same risk as class D metal fires. So what kind of packaging might solve the problem?
If a lithium-ion battery fire starts inside a passenger cabin, the crew are instructed by the FAA to not use a dry-fire extinguisher - but instead to use water or soda. This is likewise in the famous Tesla Model S fire, where the fire fighters used water instead of a dry-extinguisher. Since there is actually no lithium metal inside the battery - it is safe and won’t react with water. This is a common misconception between ltihium-ion and lithium-metal batteries. Lithium metal requires an altogether different kind of suppression system and will react with water.
Water however should only be used to stop the spread of the fire, and a foam extinguisher, powdered graphite, or CO2 are front-line methods which can be applied directly to the battery.
One may also speculate that the airlines should put protection or fire-shields between the batteries to isolate the fire. This is what happened in the Model S fire, where it was isolated to the front of the car as metal separators stopped the fire from spreading. However this simply is not feasible for shipping bulk 18650 batteries. UPS already uses more than 1,000 metal containers specifically for this purpose, and each can suppress a fire for about four hours when in conjunction with an aerosol suppression - hopefully enough time for the crew to land.
Ventura Aeorospace has developed a fire suppression system for aircraft based on foam - dubbed Cargo Foam. So far it has shown the greatest success at actually extinguishing lithium-ion fires. A telling test was performed with a whopping 192 laptop battery packs inside an AMJ cabin - and it worked, the fire went out. This foam system is used on over 60 Fedex cargo planes since 2009 - so if it works, why isn’t everyone using it?
Well that has to do with the difference between suppression and extinguishing. A fire suppression system only guarantees that a flight can make it safely to the ground and the crew can evacuate.
If that is not enough of a hurdle, one must still consider the toxic fumes which spew out of the batteries. Recently a 747 cargo flight in the United Arab Emirates caused both pilots to wear oxygen masks but they still crashed close to the airport and did not survive. After this incident full-face masks were required for pilots on several major carriers.
What all these system lacks is a true solution which can extinguish the flames. So far, the suppression systems are not powerful enough to stop a true thermal runaway event. Suppression is a soft-approach to a very hard problem.
In any case, li-ion batteries will almost certainly never be banned from sea shipment where there is far less risk. A fire will rarely spread to other containers, and surely can not damage the ship’s frame.
Battery Bro will continue blogging about new lithium-ion shipping regulations as they are made public. If you have any questions, feel free to ask in the comments section or send us an email.
]]>If you watched the video above, you may wonder why the batteries are rotating. This is much like cooking some good barbecue ribs, the circumference of the battery needs an even distribution of heat.
A team at the University of College London published a paper in Nature titled “In-operando high-speed tomography of lithium-ion batteries during thermal runaway” to better understand what happens inside and outside a battery when it overheats, explodes, and potentially causes a thermal runaway event.
Thermal runaway events are a big problem for the safety and mass-market acceptance of li-ion cells. Thermal runaway describes an uncontrollable feedback loop where an increase in reaction rate leads to more heat, which leads to an exothermic reaction, leading to a further increase in heat. This continues until finally the heat is lost in a fire, explosion, or the venting of dangerous chemicals. The temperature that may trigger a thermal runaway event is between 90 °C and 120 °C.
Furthermore, it creates the possibility of adjacent cells also initiating and perpetuating the event. This is particularly a problem on airlines, where tens of thousands of these cells are packed tightly together. Flight fire extinguishing systems are not strong enough to cope with a lithium-type fire, thus leading many to suspect thermal runaway events in lithium-ion battery fires have caused some of the world’s most notable modern air crashes. United, Delta, American, and others restricted bulk shipments of these cells on cargo flights last Christmas for this very reason.
The paper uses high-speed synchrotron X-ray computed tomography (CT scan) and radiography along with thermal imaging to track the evolution of internal and external structural changes throughout the thermal runaway event in li-ion batteries. In x-ray tomography a synchrotron is a particle accelerator which guides a magnetic field and is synchronized (hence the name) to a particle beam. You may have never heard of it, but it’s used in everything from geology, to life-sciences, to medicine. The largest synchrotron-type accelerator is - yes you may have guessed it - the Large Hadron Collider built by CERN.
This synchrotron allows the scientists to create a highly detailed image using X-rays as a penetrating wave. The X-rays are processed by a computer, and the resulting tomographic reconstruction provides a 3D model of the internal structure of the battery as it undergoes a thermal runaway event. This allows us to see inside the battery without cutting it open.
The researchers used the LG 18650 NMC type commodity cells to do their testing. What they found was a certain gas-induced degradation of the internal structure caused short-circuiting, leading to the thermal runaway. In layman terms, they saw gas pockets inside the battery. These pockets allowed the positive and negative electrodes to touch and short-circuit which helps create even more gas pockets. The author’s believe that by first identifying and understanding the problem, they can apply the knowledge to finding a solution - which is very agreeable and desirable for anyone working with battery technology.
In their experiment they found the thermal runaway even did not start until the shell reached 230 °C. There thermal imaging camera only goes up to 250, so the moment of explosion is too hot to see, however they are still very interesting videos.
If you would like to watch them, simply download them here. To read the full paper and read the authors conclusions follow this link.
Bolivia’s salt-flats have been talked about before on Battery Bro. They are some of the largest deposits of lithium anywhere in the world, and are relatively accessible. The trouble is Bolivia does not have the infrastructure of technical prowess to completely take advantage of this resource by themselves. In this light, they are seeking outside investment to develop these resources, and this week in particular the spotlight has been on German and Swiss companies who are bidding on the contract to build a lithium carbonate plant in Bolivia.
The Uyuni salt flats cover a 10,000 sq. kilometer area and is thought to be the largest reserve of its kind. This is where the 3 to 5 million dollar factory will be constructed. The lithium will be refined and turned into battery material, predominantly for use in electric vehicles.
Boliva is not the only country competing to be the primary provider of this resource - as Cobra Montana - an Australian company also released a press release this week with bold claims.
They state an aim to “control the greatest lithium resource base of any company worldwide.” There claim does not rely on the salt brine that today’s most popular mines do, but instead on something called mica. Mica comes from the latin word meaning crumb and also micare meaning glitter. They are a group of sheet silicate minerals with a tendency towards pseudohexagonal crystals. They are found all over the world, with global production at 350,000 t and have a very wide range of uses. However, lithium-ion batteries so far is not one of them.
However, technology to potentially change this is owned by Cobre for the next 26 years. The technology supposedly gives them the ability to mine lithium from mica (previously considered un-commercial) which would radically change the global lithium marketplace if it is true. This could further drive down the costs of storing energy.
Electric cars using lithium-ion batteries are here to stay. But they are still far from perfect, and one of the restraints is charging time. The Model S allows Tesla’s customers to recharge their car to 80% in about 30 minutes, but this is still quite an inconvenience when compared to a gas station that takes just a few minutes of pumping.
Stanford’s new aluminum battery prototype has a lot of potential because it can charge fully in just a minute. It is also flexible, and can bend without problem. It can be torn or punctured without any safety concerns, as opposed to most cell phone and tablet li-po batteries which would explode under the same circumstance. Lastly the cycle life of the cells is phenomenal with little degradation in hundreds and even thousands of cycles.
These are not lithium-ions, this is an aluminum-ion battery. The aluminum-ion battery perhaps holds some of the greatest potential in battery technology, but is still many years away from being commercially available.
Warehouses of batteries are popping up all over the world, in particular the United States. Recently a $10 million dollar facility was built near a small town in Washington. The reason is simple, winter storms take out the power of this tourist town every year. This significantly huts their largest industry and costs them a lot of money. The 2 megawatt facility can store enough power to keep all the lights on even during peak-usage.
The ability to keep power on is an extremely lucrative endeavor. When no electricity flows through a city, the economy also is brought to a halt and money is lost every second of a power outage. Take a country like Nigeria for example, where power in major cities can only be had for an hour a day. If the infrastructure was built to turn on electricity for the whole country, it would turn into Africa’s largest economy overnight.
The problem thus far has been the cost of lithium-ion storage solutions. They are supported by government subsidies right now, but as the cost per watt hour comes down they will be more and more accessible. Once energy storage costs are comparable to coal or gas, there will be unrivaled opportunity for places which previously has access to only unstable energy storage.
California seems to be leading the march, with a required 1,325 megawatts of storage to be implemented by 2020.
]]>For this blog post I will be comparing the ever-popular LG Chem 18650 HE2 battery with the LG Chem 18650 HE4 battery. Both are commodity cells of the same size, made by the same manufacturer.
Most people attribute the difference in model number to the first date of production, where it is of popular opinion that the HE2 first came to market, and that the HE4 is a newer version. Most people also think the HE4 is superior in performance. I’m going to have a quick look at the cells and see how these opinions hold up.
I purchased these two cells from an unnamed vendor in China who supplies some of the largest online marketplaces in the US with LG batteries.
While the following tests are interesting, they should be taken with a grain of salt. For a true comparison, many more tests should be performed with multiple cells in varying conditions.
Google Trends
To get a more accurate picture of when these batteries were introduced I decided to refer to Google Trends. This shows the very first time Google crawled either the phrase “LG HE2” or “LG HE4”.
Both cells were first mentioned in 2014, with a span of five months, the HE2 in June and the HE4 in December. These phrases are mentioned on Google 69,000 times for the HE2 and 30,100 times for the HE4.
The conclusion that might be drawn, is that the late introduction and scarcity of the LG HE4 compared with the HE2 is contributing to the popular opinion that the HE4 is newer.
Luckily, LG spec sheets list a revision history. So we see, while the HE4 is newer, it is only newer by one month, and both were released as early as 2013.
First I measure the HE2 with my digital calipers. Note the ends are non-conductive. You might want to think twice about measuring this way with metal calipers, as there is a chance you could short-circuit the battery. It measures at 65.0 mm. This is exactly to specifications on the official data sheet.
The HE2 measures at 65.3 mm. The maximum length determined by the spec sheet is 65.2 mm but I think this difference is just from measurement error on my part.
I calibrated the scale to a 100 gram weight before measuring. The weight of this HE2 battery is 44.16 grams. The weight on the data sheet reads 48.0 grams. Hmm, something seems not to be right as 4 grams is quite a notable difference.
The weight of the HE4 comes out to 45.73 grams, almost 2 grams more than the HE2. Checking the data sheet, the official weight should be 47 grams. This is within the same limits of difference and checks out.
So the question remains, why does the HE2 show such notable disparity between its actual weight and the weight described in the official data sheet?
Well it turns out the data sheet lists the maximum weight in grams. After finding a technical manual to supplement the data sheet, I found the actual weight being 43 ~ 44 grams which matches my measurement exactly. So if your numbers are off, take a closer look to see whether you are comparing to the battery's specification ratings, or to their actual ratings.
For these discharge tests we use a custom-built Arduino-based discharging unit with a special dock for 18650 batteries. It receives power through USB, with the computer plugged into A/C while testing. This enables us to record the and chart the discharge curve of the batteries. The higher amperage draw used, the lower the overall capacity will be at the end of the test. And since USB can not provide great current, each test was discharged at 2.5 amps. I did three tests of each battery, although in hindsight I should have done more.
Before I do anything I recorded the ambient temperature of the batteries. The measure 27.3 degrees Celcius. This is pretty close to the testing conditions of 25C LG performed under. I will then compare this temperature with that of the cells after they are discharged and put under a bit of stress. The energy loss in the form of heat can indicate an under-performing lithium-ion battery well.
I then fully discharged each cell down to 2.5V, and charged them using a Soshine Universal 18650 charger (green). The nice thing about this charger is the easy to read capacity display. Right away I noticed the HE2 was holding 100mAh less than the HE4. My first thought was that perhaps the LG HE2 was of a lower grade. But after the discharge tests below I reached a different conclusion.
This is the discharging unit earlier. The LED displays the current voltage of the cell after it is being drained. Looking at the chart below, this photo was taken 2.5 minutes after the test began.
Lithium-ion batteries are well noted for their flat-discharge curves. The only significant drops in voltage occur at the beginning and end of a cycle. Discharging at a steady 2.5 amps resulted in fifty good minutes of run-time, and a recorded 2397mAh worth of capacity. Checking the official data sheet, the mAh should be closer to 2,500mAh (nominal) and 2,450mAh (minimum). The cut-off was at 2.5V.
What is important to note about the disparity is how the official data sheets record capacity. The conditions of such a capacity test are set to the cell's standard discharge ratings. In the case of the HE2 the standard discharge is 500mA, with an end voltage of 2.0V. The lower te amperage discharge, the higher the capacity of the cell - this runs true in all discharge tests. For example if we discharged at 20 amps (it's maximum continuous discharge rating) the capacity would be much lower. The second note is that the tests I ran cut-off at 2.5V. If I followed the official specifications for a discharge test, this HE2 would have in all certainty met its ratings with flying colors.
On discharge test 2, there was a significant disturbance in the battery's flow of current. At first, I thought I had disturbed the equipment while taking a photo. As the device is not fully grounded, touching the metal body can modify the voltage output. However, as I noted earlier I took the photo at minute 2.5 and the disturbance happened sooner than that. The small hump you see at minute five is where the actual curve should b. So this disturbance permanently modified the resulting capacity of the cell. This time it rates at 2381mAh, 16mAh lower than the previous test.
In the third and final test the discharge looks clean and the capacity rates at 2397mAh - exactly the same results as in test 1. From this we can tell, that the capacity rating of the cell almost certainly matches with its specifications. However, the disturbance in the second test leads me to believe this particular cell is of questionable quality.
Here is the discharging unit in all of its glory. At the time the photo was taken the battery was discharged down to 3.85V.
In test 1, everything seems normal. It was discharged at 2.5 amps, down to 2.5 volts as its cut-off in the same fashion as the HE2. The resulting capacity of this test is 2493mAh. Checking the official data sheet of the HE4, we find the nominal rated capacity to be 2500mAh. This is very good news, and the HE4 is performing excellently at this point.
Herein lies perhaps the largest difference in specification sheets between the HE2 and the HE4. While the the HE2 was officially tested at a standard discharge of 500 mA and a 2.0V cut-off - the HE4 has a standard discharge of 500mA and 2.5V cut-off! The .5V difference in end voltage for the tests can easily account for a 50 to 100 mAh difference.
To refresh your memory, the HE2 had a capacity of 2397 on test 1, which is a 97mAh difference with the HE4. If I had let the HE2 drain all the way down to 2V, the capacity difference between the two cells could be totally eliminated.
The second test is done with all the same parameters and measures in at 2490mAh. This is a 3mAh difference which is only a -0.12% loss in efficiency.
In the third and final discharge test of the LG HE4 we find 2474mAh of recorded capacity. This is a -0.64% loss in efficiency.
When referring to the HE4's official data sheet I find the following about its cycle life: 300 cycles at 10 amps and 200 cycles (20A). The HE2 differs in this regards, as it is recorded at 300 cycles at 10 amps and 200 cycles (15A). That means the HE4 has a longer cycle life when put in high-drain scenarios of 20 amps, whereas the HE2 will degrade quicker at higher amperages.
So considering your application, if you are always draining these two cells at their maximum discharge of 20 amps - the HE2 will degrade quicker and will likely not exceed 200 cycles.
In conclusion, the two cells do indeed have difference albeit they are hard to notice. If you are constantly draining at 20 amps, the HE4 will last slightly longer. In terms of capacity, the two cells are equal. However, for the HE2 to maintain its 2500mAh rating it will have to drain all the way down to 2 volts.
This is from tests with LG performed on the HE2. You can see after 200 cycles the cell dips below 2000mAh - a 20% decrease in capacity - which is LG's official cut-off point for their rating of cycle life. The cell continues operating past 300 cycles but the capacity is greatly reduced at that point.
For your reference, this chart shows the typical cycle lives of 18650 lithium-ion cells.
Ambient temperature of batteries was 27.3C. After the HE2 discharged it averaged 36.5C and after the HE4 discharged it averaged 34.5C. This is not a significant difference, but the HE4 did perform slightly better in this regards.
Using the same discharging unit I can also shoot a certain amount of amps through each battery and measure their resistance for significant differences. I ran each test five times.
The HE2 measures a resistance of 49.0 mR.
The HE4 measures a resistance of 54.0 mR.
There is no significant difference between these two cell's resistances.
I did not take any pictures of this test because I did not have any hands free. I used a digital lux meter, positioned one meter away from a stand which held a flashlight. I charged both batteries to a full 4.20 V and then one by one placed each in the flashlight and measured its output in lux. The HE4 measured at 85 lux, and the HE2 at 84 lux. After one minute the HE2 settled at down at 68 lux, and the HE4 at 70 lux. There is therefore no difference between the output of these cells in this case.
The PVC tube which covers the LG HE series can be taken off, just like with any other 18650 battery. The following images can be used as a reference in identifying your own batteries. This is especially true in the case you suspect you have fake or re-wrapped battery, as the HE2 is one of the most commonly re-wrapped cells you may take off the skin of your own battery and compare it to those below to try and make a positive identification.
It is best to begin ripping off your skin at the bottom, or negative terminal. This is to avoid damaging any of the more sensitive parts contained in the top cap, or positive terminal. You can use a pin or some scissors, or just your hands. A funny side-note: the PVC smells just like balloons and is probably of similar material.
Here you can see each cell unwrapped. For the following images, the HE4 will always appear on the left. Note the HE2 has a 1, and the HE4 has a 4 marked on the steel case. These markings may vary between battery, and should not to be speculated on much. These are factory markings and indicate things like factory location, assembly line, and even which machine was used, so that manufacturers can track and debug their operations.
The top cap of these LG 18650 batteries come with white washers which protect the rim and sensitive safety circuitry underneath. The rim is where the negative and positive terminal come together and is a point of potential failure, for if he rim is pinched or a metal object is inserted the battery can short circuit and have thermal runaway. The washers are made from paper, pure white, and not overly shiny, or glossy, and of medium quality.
Both steel cases and top caps are exactly the same upon visual identification, with the only difference being the marking printed on them.
Near the top of the cell, the HE2 has a "D" printed, and the HE4 has a faded "A" printed on it. While you may speculate these are quality ratings, they are probably not and likely determine the date or location of manufacturer instead.
The final difference in markings between the two cells is that the HE4 has extra information towards the bottom end. It reads JCC2 on the top line and 2135 on the bottom line. This is probably very specific information as to where in the factory, and what machine the cell was produced. As the HE2 is lacking this marking, we can say the quality control employed on these cells is better for the HE4. This may differ from the batteries you have, and if so please leave a comment letting us know what the markings on your cell read.
If you did not follow the whole post, here are the main points from the tests:
If you are testing the HE2 and HE4 yourself at home. Remember, the standard discharge they are rated for is of 500mA. Also note that the HE4 will always seem to perform better unless you take special care to set the cut-off differently (2V for the HE2, and 2.5V for the HE4). If you are in a scenario where you are always draining the battery at 20A and want to maintain a higher voltage for as long as possible, the HE4 is the better choice.
Both cells are currently available on the marketplace. However the HE2 is in very high production, while the HE4 is much more scarce. The HE4 is generally between 50 cents to two dollars higher in price per cell. I have heard rumors from a large factory that the HE4 was a limited production run, intended for one client and that it is no longer in production. As the cell can currently purchased, I can not confirm this rumor. But if the HE4 becomes more difficult to find in the future, this may well turn out to be true.
There are no official pulse ratings for these cells to be found in any specification sheets. Many battery vendors claim that the HE2 has a pulse rating of 35A. This is most likely entirely fabricated. A pulse rating is meaningless without two variables, the first being amperage, and the second being time. As a pulse denotes a certain amount of time, without this variable the rating is not useful. Generally in tests I have seen for the Samsung 25R, a 35A pulse will last only about one second. It is important to keep this in mind, as the HE2 most likely matches this specification, if it does at all. Also when pulsing at higher than max. continuous discharge the cells will degrade more quickly. If constantly pulsing at 35A for 1 second, the cell is likely to only last a maximum of 100 cycles rather than its full 200 because of the added stress.
These batteries should only ever be safely discharged at a maximum of 20A, as the manufacturer does not indicate what the safe pulse discharge ratings are. Added stress from exceeding ratings can cause the cell to fail, catch on fire, explode, and have a thermal runaway event which is very dangerous.
The chemistry of the LG Chem HE2 battery is: Chemistry Li[NiMnCo]O (H-NMC) / Graphite + SiO. I can not find an official reference for the chemistry of the HE4 unfortunately. The HE2 is an NMC (nickel-manganese-cobalt) battery. NMC is inherently safer than other chemistries, and finds its use in e-bikes, power-tools, military, and even medical devices.
The dominant negative electrode (anode) material is graphite which is normal for lithium-ion cells. The second part of the negative electrode is made up of (SiO) Silicon monoxide which is a more unique inclusion. The inclusion of SiO particles in the carbon form a network of randomly distributed pores with sizes in the nano-meter range. This translates to reduced surface activity, which is important. In graphite anodes, the lithium ions travel to the outer edges of the sheet before coming to rest, and this route takes so long that there is congestion around the edges. Reducing this congestion foremost has shown to increase the cell's cycle life.
You may compare it to other chemistry types with this helpful table:
I hope you enjoyed this little look at the differences between the LG 18650 HE2 and the LG 18650 HE4. If you would like more information, or more posts like this, or have any questions or comments please leave a comment on this blog post. Thanks!
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