Multicomponent Li-NMC 26800 Yuliang 3.7 V 7000 mAh batteries

Battery manufacturers have come up with an enormous number of different form factors over the years, but they still keep surprising us with something new.
It seems like only recently that 21700 and 20700 cells became widely available, and things had settled down. But then I got my hands on some cells that differ not only in size (26800), but are also advertised as multicomponent.
Well, let's test them, heat them up, freeze them, and see what they're all about.


These batteries are a type of multicomponent cell — lithium nickel manganese cobalt oxide (LiNixMnyCozO2) batteries. The full name is hard to remember, so the abbreviated name Li-NMC is used.

Specifications from Wikipedia
Specific energy: 150–200 Wh/kg[2][3]
Charge-discharge cycle life: over 1000.
Voltage
maximum per cell: 4.3 V (fully charged)
nominal: 3.7 V
minimum: 2.6 V (fully discharged)

But besides their chemistry, these cells also differ in form factor: 26800. That means they're similar to the familiar 26650 cells, but 15 mm longer. Since this is something new, I was doubly interested in testing them.




Specifications from the store page.
Brand Yuliang
Type LiNiCoMnO2
Capacity 7000 mAh
Continuous discharge current 20 A
Maximum discharge current 34 A
Internal resistance < 10 mΩ (AC 1000 Hz)
Upper voltage 4.2 V
Operating voltage 3.6 V
Lower voltage 2.75 V
Nominal charging current 6 A
Cycle life 1500
Operating temperature range -30 to +55°C
Dimensions: 26 × 80 mm
Weight 115 g

Batteries of the same size are also available with a capacity of 6800 mAh, and they're a little cheaper.

The heat-shrink wrap is a distinctive light green, similar to the color used on ANR26650M1-B batteries, but with one notable difference: it doesn't cover the batteries completely.
Each battery has a unique serial number and matrix code to help protect against counterfeits.
The positive terminal is flat and three-pronged, and the safety vent is visible.



Dimensions and weight.


While getting ready for the tests, I ran into a bit of a problem: my holder isn't designed for batteries this long. Of course, I could have bought the extended version in the first place, but who could have guessed I'd need to test batteries this long?
Some time ago, though, I bought reinforced terminals for it. The positive one is noticeably shorter than the original, so my first thought was simply to replace it.
Easier said than done. During testing a few months ago, I somehow overheated the holder badly enough that the positive terminal melted right through the plastic, so there's now a piece of fiberglass board in there.

In the end, I hit a snag: I couldn't unscrew it. But I found a workaround—unscrewed the stop on the moving part and simply pushed it farther back :)



My auxiliary charger also had trouble with the batteries' length. It can fit even protected 21700 cells measuring 75–76 mm, but 80 mm cells simply wouldn't fit, so I ran the “normalization” cycle on my main battery tester.

The batteries arrived fully charged—or, I'd even say, slightly overcharged. Apparently, my particular samples were tested before shipping.


The specs list a single charging current: 6 A. At that rate, charging takes 1 hour 42 minutes, and you can see that the CV phase took up a fairly large part of the time. This usually indicates high-capacity batteries.
For the tests, I charged them at 5 A, since that was the maximum current supported by the EBC-A20 tester, but I don't think it makes a critical difference.


The batteries are rated for a maximum continuous current of 20 A (almost 3C). I tested them at 0.2, 0.5, 1, and 2C, as well as at 20 A.
With a rated capacity of 7000 mAh, the first sample delivered almost 7200 mAh, which is very good. However, at 20 A, there was a noticeable voltage sag.


The battery temperature at 14 and 20 A was 60 and 75 degrees, respectively, which I think is pretty good.


The second sample produced results almost identical to the first.


The temperature was also identical.


And everything looked good, but after the first test at 20 A, it turned out that the heat-shrink wrap on the battery had gotten even shorter. In the photo, this is the second cell; it was the first to undergo this test.


I even considered filming the second test, but decided to stick with thermal-camera photos.
The temperature at which the heat-shrink tubing starts to creep is around 69–70 degrees. In the photo, you can see that it is still in place at 68, but has slipped off by 74.

I suspect this is partly because it doesn't initially extend all the way to the bottom of the battery.


I also had no complaints about how closely the cells matched: they were practically identical, so these batteries should work well in packs.


Since this was my first time with batteries using this kind of chemistry, I checked their self-discharge out of curiosity. It was a very rough test: I fully charged them, waited almost three days, then started charging them again.
The second charge took 54 and 34 mAh for the first and second cells, respectively, which is a pretty good result.


I decided to take things further and see how these batteries perform at low temperatures. I remember being disappointed once by the cold-weather performance of inexpensive LTO cells.

I put the batteries in the freezer, where they cooled to around -20–22 degrees.
The first cell cooled for about 6 hours, and the second for three hours longer. The temperature was measured after 6 hours.


Impedance of the batteries while cold. You can see that condensation formed on them and was literally freezing as I worked, so I had to take the measurements as quickly as possible.


I tested the first battery at 1C and the second at 2C. I have to admit, I expected worse results.
The result for the second cell (red graph) was predictable: even at normal temperatures, 2C is close to the limit for high-capacity cells.
The first cell (blue graph), on the other hand, did sag at 1C, but still performed well, delivering only 15% less capacity and 20% less energy than at normal temperature.


During discharge, the first cell warmed up to around 3–5 degrees, while the second reached 36.


Battery impedance as received, after “normalization,” and after all the tests. There is a small difference, but it is within tolerance.


Conclusions.
I really liked these batteries, especially considering that their capacity is equivalent to 5600 mAh in the 26650 size, and they perform very well even at low temperatures.
The specified maximum continuous current is 20 A, but I would limit it to 2C (14 A). In my opinion, that would significantly extend their service life and increase the energy delivered.
That said, based on my estimates, they still lose out to 21700 batteries in terms of volume-to-capacity ratio, equivalent to 4000 mAh in that size—and 5000 mAh cells are already available.

The only thing I would criticize is the odd heat-shrink tubing: it doesn't fully cover the battery, and it slips off at temperatures above 70 degrees.
It's probably also worth mentioning that these batteries are only suitable for devices with a built-in charger or for battery packs, since finding a charger that can accommodate them will be very difficult.

In short, these are interesting batteries, particularly well suited to electric vehicles and possibly power tools.

As last time, the store is offering a 5% discount on any batteries if you provide the code “kirich” when placing your order, by any convenient method. I don't think anyone would turn down a little extra savings.
I was also told that although the store is Ukrainian, you can ask about the possibility of shipping to Russia.

That's all for now. I hope you found this useful.