Do small Li-ion cells heat up as much as large ones at high currents?

[mudman cj]

I have noticed that many people report using 10440 cells at rates as high as 3C in lights such as the Fenix LOD-CE, which I understand can pull 1 Amp from the approximately 320 mAh cell. My question is if there is data to indicate that small cells such as this remain at lower temperatures than other cell sizes when supplying a given multiple of their respective capacities (C).

I suspect that geometry may be the characteristic of a 10440 that has allowed so many people to use them at 3C without reports, as far as I know, of overheated cells venting with flame. You have to admit that heat doesn't have very far to travel in a 10440 before getting to a surface where it can be dissipated (averaging over all possible paths). But then again, perhaps everyone has enough respect for Li-ion cells to avoid using them for too long. I do hope that this type of use is not an accident waiting to happen. The thought of holding a Li-ion cell at 3C between my teeth make me feel a bit 😱.

So, has anyone seen data comparing cell temperatures as a function of current times a fixed multiple of C? If not, does anyone have the proper equipment to measure it?

 

[Trekmeister]

Can't speak from flashlight battery experience, but simple geometry tells me smaller cells should be able to handle heavier (in respect to C) discharges better since the relationship between surface area and volume favours the smaller cell when both have the same cylindrical shape. (and breath in... that was one long sentence!)

For example, while not cylindrical, the small LiPo-cells (a hundred mAh or thereabout) in pizoZ RC helicopters are discharged in 5-10 minutes without any obvious ill-effects. That is a discharge rate of up to 10C and they barely even heat up.

 

[mudman cj]

That is precisely what I was thinking. In more detail, the temperature of the cell is related to the rate of heat in compared to heat out, where the heat generated is proportional to the volume and the heat dissipated is proportional to the area. As the cell radius decreases, the volume term decreases faster than the surface area term because the volume is proportional to r^2 and the surface area is proportional to r.

 

[Fallingwater]

For example, while not cylindrical, the small LiPo-cells (a hundred mAh or thereabout) in pizoZ RC helicopters are discharged in 5-10 minutes without any obvious ill-effects. That is a discharge rate of up to 10C and they barely even heat up.

Actually, while even the cheaper LiPo cells can certainly deliver 6C or more, you can hardly say there aren't ill-effects. Hard-discharged LiPo cells have a useful life of around 100 cycles, against the 500 or so of LiIons that get discharged relatively gently. And that's just the official number, supercheap tiny cells such as those in Picoo Z helicopters and their clones are known to not even achieve that number.

And they do heat up. I can't speak for the tiny PZ ones because those are inside the heli when it flies, but the 2S 800mah pack of my Walkera 5#4 becomes almost unpleasantly warm after a few minutes of flying.

In other words: a 10440 cell can withstand hard discharging without blowing up, but it's being severely beaten and will very likely give you a short service life.

 

[65535]

A quote from silverfox comes to mind..."batteries don't die, they are tortured until they give up" something along those lines.