Question about Li-Ion Capacity

Noob question.

The approximant mass for an 18650 (taking off 2mm for button top) = 16.03 cc, 18500 = 12.21 cc, 14500 = 7.40 cc, the 18500 has 76.2%, and the 14500 has 46.2% of the mass of 18650. If there are 18650 with a capacity of 2400 mAh, why aren't there 18500 and 14500 batteries with the equivalent capacity, or 1800 mAh 18500 & 1100 mAh 14500?

Looks like in the future there will be 4000 mAh 18650 (Link). It would really be nice if there was 18500 and 14500 with equivalent capacity. :twothumbs

Would this be because all the research is being done on 18650 or are there any other reasons?:thinking:

palomino77 said:

Noob question.

The approximant mass for an 18650 (taking off 2mm for button top) = 16.03 cc, 18500 = 12.21 cc, 14500 = 7.40 cc, the 18500 has 76.2%, and the 14500 has 46.2% of the mass of 18650. If there are 18650 with a capacity of 2400 mAh, why aren't there 18500 and 14500 batteries with the equivalent capacity, or 1800 mAh 18500 & 1100 mAh 14500?

Looks like in the future there will be 4000 mAh 18650 (Link). It would really be nice if there was 18500 and 14500 with equivalent capacity. :twothumbs

Would this be because all the research is being done on 18650 or are there any other reasons?:thinking:

Click to expand...

The bottom line is that most of these other cells (besides the 18650) are basiacally based on older chemistries and methodologies. When new technology comes out it will be applied to the 18650 first .

A good example of this is AW and his 18650's he actually has two cells for sale the older one and the newer higher capacity one. The higher capacity one is base don older chemistries and technologies.

Others will chime in with more details.

palomino77 said:

Would this be because all the research is being done on 18650 or are there any other reasons?:thinking:

Click to expand...

Well, to be particular, it's about development, not research. But yeah, that's the reason for the large discrepancy -- 18650s are used in laptop batteries, power tool batteries, and EV/hybrid applications (along with 26650/26700, except for laptops), so those sizes see improvements first.

There is also an inherent loss of capacity with smaller cells, because packaging (and probably some internal features, as well) don't scale down with the overall size (square-cube rule), and thus "waste" more space in smaller cells. But this effect is relatively small for, e.g. 18650 vs. 18500.