High-capacity packs using 18650-format cells have become popular, and we will have some interesting options soon with the new 21700 cells that are just now becoming available.
Some EV battery history
Many years ago in the early 1990’s (just when GM was confiscating and crushing the existing EV1’s), the founders of the start-up called Tesla were test-driving the T-zero prototype and contemplating what a successful electric car drivetrain would look like.
I am normally skeptical about most conspiracy theories, however…I read that at that time, the most common large-format battery was the NiMH cells that were used by the Toyota Prius and the Ford EV Escape. The global oil-conglomerate Chevron-Texaco purchased a controlling interest in Cobasys, who had owned the patents on those cells. I had hoped at the time that this indicated a shift in the powerful oil-company paradigm of their recognizing that they needed to evolve, and become a big player in the EV field, instead of competing with them. Someone with “big money” was finally investing in EV’s!
Instead, their newly-found control over the large-format NiMH cells was used to severely limit their use. This forced Tesla to focus on using thousands of small 18650 lithium cells as the next best alternative. This ended up being a good thing. In spite of the extra time and effort to design and manufacture a large pack out of thousands of smaller cells…I am only recently seeing the benefits of how heat affects lithium cells (and having many small cells helps their heat-dissipation), and how individual cell-fusing means that…if one tiny cell out of thousands fries, the pack as-a-whole will continue to work safely.
Lithium-based 18650 cells (18mm diameter, 65mm long) came-to-fame as the cell of choice to power laptop computers and cordless tools. Laptop cells compete on lowest price, but…it is the cordless tool cells that compete on performance and long run-time. Those are the premium cells that ebikes need and love.
What about 26650’s?
The 26650 format already exists (26mm diameter, 65mm long), and I have occasionally read of people who wondered why Tesla (and others) didn’t just use this existing format. I honestly don’t have a solid answer, but the most likely culprit is that a fatter cell has a lower ability to shed heat that is located at its core. In fact, a 26700 cell format already exists too (26mm diameter, 70mm long)…
I recently wrote about the Lithium battery lecture by Prof. Jeff Dahn, and heat-management is one of the major factors in getting a battery to last as long as possible. Tesla has an unprecedented 8-year warranty on their packs, which is pretty amazing, so…they are doing something right (note: keep your battery cool, and charge to 4.1V per cell).
There are a lot of ebikers who would prefer using 26650 cells…if…they came in a variety of Ah’s and amp-producing versions. However, the 26650 cell selections that are available now are very slim-pickins at best.
The INR prefix is generally regarded as designating that a cell chemistry is “NCA” or Nickel Cobalt Aluminum. This is what Tesla uses (but…there are also several variations on the NCA recipe). The NCR prefix is the “NCM” chemistry, Nickel Cobalt Manganese. Listed below are the recently popular high-capacity cells on the market.
10A, 3.5-Ah, NCR18650GA Panasonic / Sanyo
10A, 3.5-Ah, INR1865035E Samsung
10A, 3.5-Ah, INR18650MJ1 LG
When these companies say that a certain cell is “rated” for 10A continuous…what does that actually mean? It may be listed as a “continuous” current rating, but…if you draw 10A continuously, what actually happens (does it get hot, or only warm)? Clearly, these cells can temporarily output a higher level of amps than that for a few seconds, but…factories don’t like to advertise that…using them that way will erode their range, and also some of their life.
I’m still annoyed that every major battery manufacturer has not been honest and forthright about how charging to 4.2V per cell will dramatically reduce the life of your expensive pack (every “official” factory spec sheet still lists the charging volts as 4.2V per cell…WTF?). This is the default charging level for the battery chargers that are commonly purchased. By charging to only 4.1V per cell, you might be able to double the life of your expensive battery pack (OR MORE!). Are there any lithium pack chargers that will balance every cell when only going to 4.1V? If no, then…why not?
This is the truth, regardless of the brand of cell, or vendor that you like. As a result, I prefer to design my personal systems to use a cells “factory continuous” rating as my “temporary peak” rating. My packs run cool, they provide the max miles possible, and…they live a long time.
That being said, I am collecting information about the HEAT that results from the current draw on various popular cells. In my mind, the resulting heat is what actually determines a cells amp-producing capability. So…why can’t I find a chart of amp-draws and the resulting heat for popular cells? Maybe something that is easily repeatable to verify it’s accuracy?
The three cells I listed above are the most popular for range, and I suspect they will grow to be even more popular over time, due to their fairly decent performance (a reasonably small 4P pack of 10A cells can produce 40A…nice!). However, if you are a hot rodder…the cells below are on the short list of high-amp “hot rod” cells I have recently seen to be frequently used.
15A, 3.0-Ah, Samsung 30Q
20A, 3.0-Ah, LG Chem HG2
20A, 2.5-Ah, Samsung 25R
30A. 1.5-Ah, LG Chem HB6
30A, 2.5-Ah, Sony VTC5
I am listing high-capacity and also high-amp 18650 cells here, so you can compare them to the evolving 21700 cell options that are just now becoming available.
Panasonic 20700’s/ Tesla 2170
The history of formats is a subject that can give me a headache and indigestion whenever its brought up (VHS vs Betamax, DVD vs Bluray, etc). If I was consulting for any device manufacturer, I would push the 21700 format (21mm in diameter, 70mm long). For some reason that only Panasonic knows, they have come out with a very minor variation of a 20700 cell (20mm diameter, 70mm long).
One millimeter is roughly 1/25th of an inch, so…if you have both a 20700 and 21700 cell in your hand, you probably couldn’t tell the difference between them, but…these kinds of proprietary variations drive me nuts. Samsung even now has a 20650 format (there are various reports that the 20650 format was started, and then discontinued…who knows? LG has a model 20650 M42 = 15A and 4.2-Ah, model 20650 HG6 = 20A and 3.0-Ah).
This means that once a consumer buys a certain device, they are then (hopefully) locked-in to buying only a certain format of battery cell. The joke is on them, because China is famous for filling-in any weak business strategy gaps. A small adapter can be added to make a 20650 cell fit in a 20700 slot, and a 20700 cell will easily fit in a 21700 slot. If you are designing a device that you want to be relevant over the next decade, make the slots to fit the physical dimensions of a 21700 cell.
The Tesla car company is the proverbial 500-lb gorilla of the evolving EV market. When they sneeze, everybody in that world gets a cold. A short while ago, they announced that they would partner with Panasonic and build a huge factory to produce cells for the next generation of Tesla cars, and this new “Gigafactory” would be located in Nevada, USA.
That factories’ production capacity initially sounded a bit optimistic, but then…Elon Musk announced that Tesla would be producing a “power wall” device (a flat, wall-mounted battery pack), that would also eventually use those same cells. This power-wall bank of cells can provide power to your home during a temporary power outage. It can also charge up in the middle of the night (when electricity is cheapest) and then assist during the high-demand part of the day. This allows states to build fewer electrical generating stations in the near future.
Of course, the powerwalls’ primary market is as a storage device, so home-owners can soak-up solar energy with PV panels when they are at work, and then draw from the battery pack in the evening.
Back in the early days, it made sense that Tesla should use an existing battery cell format (even if Chevron hadn’t limited them), but now?…their huge cell-production projections meant that they can easily afford to create an entirely new format that is maximized to meet the demands of their near-future EV designs, and also the Tesla power wall.
That new format is the 21700 cell (sometimes referred-to as the 2170 cell in many places). It has been claimed to have 40% more active battery volume, even though it is only slightly fatter and taller. That is more believable once you realize that there are components inside the 18650 cell that remain the same size in the 21700 cell, so…every aspect of the size increase is solely made from the active battery material alone.
OK, who is driving this?
The Tesla Model-3 EV is reported to be the first vehicle that will use the 21700 cell. Demand from the Model-3 assembly line is assumed to be so comprehensive that it may be a while before the Power-wall devices and other Tesla EV models can start using this new cell from the Gigafactory. As of June of 2017, it has been reported that the Tesla Gigafactory in Nevada is finally in production of the 21700 cell.
If you haven’t heard of the “Lucid” car company (formerly known as Atieva)…you will soon. They are about to produce an attractive electric sport-sedan in 2018. That may sound optimistic for a start-up that few have heard of, but…they are also the sole supplier for the batteries used in the 2018 Formula-E electric race series. This will be a collaboration between McLaren, Lucid, and Sony, so…this is not vapor-ware…and they are contracted to use Samsung 21700 cells!
Just like the 18650 cells that these top-5 companies produced before (Panasonic, Sanyo, Sony, Samsung, LG-Chem)…there are cell-models that are optimized for capacity, and also a variation that is adjusted to have the maximum current (high-amps).
You might assume that EV sports cars will be using the performance version of these 21700 cells, but…they use so many cells per vehicle that they can get very high pack-amps from a cell that provides lower amps-per-cell, but…very high capacity. This benefits all EV’s because…E-motorcycles, E-Scooters, and ebikes will all benefit from these new cells that significantly increase range, while still providing awesome performance. The higher-amp version of these cells (with slightly less capacity), have been spec’d by cordless tool manufacturers (see below). Since we can now have higher capacity or higher amps, from a cell that is only slightly larger? This is good for all ebikers and ebike manufacturers.
[side note: there are minor issues with every website that provides tech information on any new development. We can either wait until every detail is exhaustively proven, or scan several sources to try and obtain a reasonable opinion based on an average. Exercise caution, but…here is what I found, as of June 2017]
First up is the Japanese company Panasonic, simply because they are so big…and also because they took the bold move to risk billions of dollars by investing with Tesla and helping to drive all of these new changes. they are producing the 21700 cell for Tesla, but…in the general marketplace, they are claiming to produce the 20700 cell. This is confusing, but…lets roll with it for now…
They are currently offering what they are referring to as their A, B, and C cells. The “A” cell has the highest amps at 30A, the “B” cell has the most range at 4.2-Ah, and then…the 3.5-Ah “C” cell is somewhere between the two, so…they have an option for whatever your priorities are.
30A, 3.1 Ah, NCR20700A
15A, 4.2 Ah, NCR20700B
Since Sanyo is now owned by Panasonic, there is a considerable amount of overlap in their product line. The Panasonic “A” cell has the same specs as the Sanyo 20700, sooo…they likely came from the same assembly line, using the same exact design (30A, 3.1-Ah, NCR20700A)
However, whether the PVC heat-shrink plastic-wrap that covers the cell says that it’s a Panasonic or a Sanyo, here is a review from a vape forum:
“…At 30A continuous the temperature rose to 75°C. This is just below the average temperature for a cell being discharged at its continuous discharge rating (CDR) but the datasheet seems to show a higher sensitivity to temperature than our 18650’s so I am not giving it a rating above 30A...”
If you want to run a Bafang BBS02 or a BBSHD at an occasional 30A peak, while using a 14S (52V) battery configuration?…this cell can provide that with only 14 cells. THAT…is amazing (of course, a 1P pack would have extremely short range, but..it can be done)
Panasonic calls the NCR20700B a 4.2-Ah cell, and Sanyo calls it a 4.0-Ah cell, but…either way it’s a significant bump over 3.5-Ah 18650 cells. Most “max” range tests drain the cell at a very low amp-rate, but…experienced builders know that the harder you pull the amps, the lower the full range of the cell you will get. This is the truth, regardless of what brand of cell you want, or which vendor you buy from.
HOWEVER!…I think that for these 21700-sized cells, the configuration that will be the most interesting for us is the high-capacity 4.0-4.2 Ah version. This is because…these still have enough amp-producing power to be very useful in the size of packs we need and can fit on our frames. As long as a certain number of cells fit and give us the pack-amps we need…why not go for more range? Trust me when I say that you will not regret buying extra range in your next battery pack…
“…At 15A continuous the temperature rose to 74°C. This is just a bit below the average temperature of a cell operating at its continuous discharge rating (CDR). This is an indication that we are operating near its true rating…“
Let’s compare a common 14S / 5P battery pack made from 18650 GA cells, and a slightly smaller 14S / 4P pack made from 20700 Panasonic B cells…
52V, 17.5-Ah, 50A, 70 cells (18650 GA)
52V, 16.8-Ah, 60A, 56 cells (20700 B)
This is where the 20700 shines. Any extra length (70mm vs 68mm) just makes the ebike battery packs a hair wider, since most packs place the cells left-to-right, on their sides (from the perspective of a rider sitting on the ebike saddle). The pack will be a negligible 1/12th of an inch wider between your knees, when riding. That leaves only the diameter of the cells to be concerned about.
If you can squeeze-in a 5P 20700 pack, then the small extra height will only be 2mm X 5P = 10mm, roughly half an inch taller and longer than a 5P 18650-cell pack. But…if you couldn’t quite squeeze a 5P pack onto a frame you like, you might be able to fit a smaller 4P pack of 20700’s, while still having 4P X 15A = 60A of power (of course, if you could fit a 5P pack, then 5P X 15A = 75A…not bad!)
Samsung is a respected cell supplier from South Korea. They had previously used pouch cells for their large-format EV batteries, but now they have seen the light. Here’s a quote from a review by a vape forum, on the Samsung INR2170030T
“…Its temperature of 78°C at 40A continuous is the average for cells being operated at their rating so I am rating this cell at 40A…”
They also stated that the cell could provide a few seconds of a 60A burst. Not bad for a single 3.0-Ah cell
Here is another review of the 30T cell by a flashlight forum (yes, that is a thing that exists).
Samsung has begun producing a “48G” cell, and it is rated for a capacity of 4.8-Ah per cell. Early samples suggest the extra capacity inhibits max current, so they should be able to achieve their rated cycle-life if limited to 7A continuous and 10A peak. It can do more, but…it would get hot and would not last as long.
Right now its hard to purchase authentic Sony VTC cells (which are fantastic). The only way to be 100% certain of getting those without also getting a few counterfeits mixed-in is to buy cordless tool battery packs and to cut out the cells. So…what has Sony got planned for the new 21700 format? They partnered with the German firm “BMZ” and plan to make the “3Tron” 21700 cell in Karlstein-Großwelzheim, which is near Frankfurt, in central Germany.
BMZ Press Release from 21 September 2016
“…In producing the super cell, BMZ co-operates with the world’s leading cell manufacturer Sony. Its manufacturing expertise with more than 300 million cells annually guarantees top quality. The assembly of the 3Tron batteries will take place at BMZ – Europe’s new gigafactory. With a footprint of 55,000 m², it is Europe’s largest battery factory…“
Sony has announced that it will be a 5.0-Ah capacity. If an 18650 cell can hold 3.5-Ah, it is not crazy to suggest a 5.0-Ah 21700 cell is possible, but that is sounding like it is near the theoretical maximum (using current chemistry and packaging methods), and it is a serious 43% increase in capacity.
XXA, 5.0-Ah, US21700VXX
[I will update this listing when more information becomes available]
Operating out of Maple Ridge, British Columbia, Canada, “E-One Moli Energy (Canada), Limited” is a division of the E-One Moli Energy Corporation of Taiwan. Established in 1987, E-One Moli-Canada is one of the few manufacturing plants producing rechargeable lithium-ion batteries in North America.
E-One Moli has announced that they will also be making a 20700 cell, but they are not posting who (or what) they are making it for. At various times in the past, E-Moli has supplied cells for Zero motorcycles, Milwaukee Tools, and the US military.
35A, 3.0-Ah, INR20700A
Where to buy them
As usual, any retailer who is willing to sell individual new cells is charging a premium. This is for the global vape and flashlight market. If you want to buy 80-100 cells to make an electric bike battery pack, make sure to contact their customer service, and you might get a better bulk-purchase price.
The blogger “Syonyk” posted that he wanted to acquire some 21700 cells and then he purchased a new DeWalt 20V XR 6.0-Ah cordless tool pack, and gutted it. As of June 2017, Amazon is listing a single DeWalt DCB206 pack for $83, and a “2-pack” for $138. Since we would want a LOT of these cells for the lowest price, lets look at the multi-pack for $138.
Pic courtesy of syonyk.blogspot.com, please give him a few clicks, so he will keep doing awesome stuff like this and posting the results. Each one of these packs holds ten of the Panasonic / Sanyo NCR20700A’s, so…30A and 3.0-Ah each. This pack in a 5S / 2P configuration is 18V, 6.0-Ah, and can safely provide 60A! Since its $138 for two, thats $69 for one pack, and brings the cell-price down to $6.90
But, as good as that is (with many retailers demanding $9-$10 each)? in my mind, the best part is that…these come with spot-welded tabs from the factory. If you gently cut the connecting tabs with a thin disc on a dremel, you can solder onto the cut-end of that tab without any heat damage to the cell, like our friend Doctor Bass shows, here. I have read reports that the bus-plates are nickel-plated copper, in order to handle the higher amps.
If you want to shop around for other brands of cordless tools (if DeWalt is sold out when you need them), I found this quote on the web:
“Bosch 18V 6.3 Ah EneRacer battery pack uses NCR20700A
Metabo 625343000 18V 3.1 Ah LiHD Battery Pack has 5 NCR20700A’s
Metabo 625341000 18V 6.2 Ah LiHD Battery Pack has 10 NCR20700A’s
Metabo 625344000 36V 6.2 Ah LiHD Battery Pack has 20 NCR20700A’s”
If you want to try this, I’d recommend you buy only one, gut it yourself, and…if it turns out to be what you want, buy as many as you need immediately, before they change anything about the packs you want.
Vape and flashlight suppliers:
IMR batteries dot com, they have the 20700A for $8, and the 20700B for $10 each
Fasttech dot com, they have the 20700A for $9
illumn dot com, they have the 20700B for $10
Counterfeit Cells are Everywhere!
Only buy name-brand cells from a trusted vendor (Panasonic, Sanyo, Samsung, Sony, LG-Chem). Here is a pic of an “off brand” 18650, but…cut it open and the reason for the tiny capacity is obvious. A small generic cell is hidden inside an 18650 shell. 21700 cells are the hot new item, so…if the price from an anonymous vendor seems too good to be true…
What’s Next for Batteries?
I think as soon as 21700 cells start to become more available, that will put pressure on the 18650 market to lower prices a bit, making the option of an 18650 pack still relevant for the next couple of years. That being said, you are going to be hearing a lot about 21700-format cells in 2018, as the exciting new thing.
I can visualize 18650 and 21700 cells remaining the staple of ebike packs for the next decade, but for E-scooters, E-motorcycles, and large auto EV’s, the big breakthrough I am most waiting for is the Solid State Battery (SSB’s). They currently work in the lab, and the only delay is simply finding the cheapest way to manufacture them. They are scheduled to be in production by 2020.
By making the electrolyte a solid, battery pack volume can be reduced by 1/3rd (if not more). Or, conversely…you can have a battery pack the same size, with roughly 50% more range. The Tesla Model-S is currently rated to have over a 200-mile range, so…having near 300 miles would be pretty amazing.
As far as what possible improvements are doable beyond SSB’s in 2020, I don’t know, but…Tesla has at least eight patents on metal-air batteries. Kinda makes me wonder what they’re up to, right?
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Written by Ron/spinningmagnets, June 2017