Why 21700 instead of 26650

[Photon]

21700 seems to be the new standard in Li-Ion batteries. Why 21700 instead of 26650, which have considerably more volume and therefore greater capacity?

 

[fulee9999]

I would assume it has to do something with the fact that the most common li-ion is 18650, some devices accept and/or can use 21700 rechargeables, but there is just a very small portion of devices that can fit/handle a 26650 battery

 

[lctorana]

I thought it had something to do with being used in electric vehicle battery packs, and we get the seconds and castoffs, but that of course doesn't answer the question why that cell was chosen for that use, and not say 26650 or 32650.

 

[degarb]

I also recall that weight to energy density was better in the 21700, and nearly that of the top of the line name brands of the 18650.

Because, I wear all my lights on the head or wrist, I am not willing to settle for less energy density.

I personally would not be interested in reducing energy density unless the cell had at least 10 amp hours.

 

[Hooked on Fenix]

A lot of the high end lights are designed to be 1 inch diameter to fit to mount onto a gun. A 21700 just makes the cut. A 26500 does not.

 

[xxo]

Volumetric energy of 26650's are not very good compared to high capacity18650's. 26650's have a little over 2X the volume and only a little over 1.5X the capacity. 21700's still do not quite match the energy denisty of the best 18650's but they are close and seem to be getting closer.

26650's would likely be better if they were more widely used in industry and being manufactured by the big Japanese and Korean battery makers.

 

[fulee9999]

correct me if I'm wrong but doesn't 26650s gold the same amount of charge as a 21700?

 

[Lynx_Arc]

I think a lot of it is that the 21700 was manufactured originally for EV use and because of that the cell is more optimized than the 26650. Likewise the 18650 was also an EV favorite that the 21700 replaced. The advantage in a smaller diameter makes for better use in packs using multiple cells. Tool batteries have become a use for the 21700 cells now as the packs are a little larger all around but the higher capacity and current handling capability makes them popular. I have some 3A and 6A 21700 batteries and they rock. They make single layer 20V 4Ah dewalt batteries which with 18650 take 2 layers or 10 cells, they do have a 5A 2 layer battery but for the 6A you have to go 3 layers with 18650.
I also have 8A 2 layer 21700 packs and they make 10A 2 layer packs. I don't see a good way to use 26650s to make packs similarly they would be taller with no more power.

 

[KITROBASKIN]

How about a 3.2V LFP 38120?

 

[Lynx_Arc]

How about a 3.2V LFP 38120?View attachment 31668

(To me) what matters is power density and availability (cheap) as some of these odder sizes one day may be unobtainium or high pricedium.

 

[etc]

I think 21mm is the best most user friendly format. I hope it becomes the de facto standard.

 

[fivemega]

Why 21700 instead of 26650, which have considerably more volume and therefore greater capacity?

Physical size and weight.

 

[Dave D]

The step up in body size from a 18650 flashlight to a 21700 is minimal compared to the increase in mAh that is provided, from 3600 to 5000 mAh's, which is an additional 39% in capacity.

Compare a 18650 flashlight to a 26650 and the flashlight body would need to be 'C' cell sized which is a substantial difference and would be too large for most people to EDC, even with an additional 67% increase in mAh's.

The 26650 (6000mAh) would provide a 20% increase in mAh's over a 21700 (9500mAh).

 

[Olumin]

For larger multi-cell lights in a traditional in-series configuration I would prefer 26650 for its improved ergonomics (wider battery tube). The slight increase in capacity is a bonus.

For single cell lights I prefer 21700 because of their smaller size & weight.

 

[brachypelma44]

correct me if I'm wrong but doesn't 26650s gold the same amount of charge as a 21700?

More, actually. The Vapcell K62 is 6200 mAh. The highest 21700 cell I've seen is 5000mAh.