It'll take someone more knowledgeable than me to explain why a prismatic would unroll like TP... I thought they were all pouch cells too.,,,it was like unrolling toilet paper. It didn't look like pouches to me.,,,
Thanks for the feedback!IMHO following is not very clear:
"Below 72°F the effect is linear. Over 72°F the effect becomes exponentially negative."
Does the "exponentially negative effect" refer to the capacity fade that will become bigger over 72°F ?
Or to the effect of compressing ?
|I see what you mean... I went back to the source where @ghostwriter66 wrote:|
But that didn't quite make it clear and quite possibly I paraphrased it incorrectly.
So I did some digging and found this paper (Lithium, but not LFP) and while the temperatures were extreme it had the table off to the right which seems to indicate compression isn't important at low temperatures in regards to fade, so I've updated the wiki entry ... hopefully clearer/accurate...
I don't see how the jelly roll can be compressed. Compression helps prevent delamination of the jelly roll because it expands and contracts when the cell is being charged or discharged. That's my understanding.
Because it's not cylindrical, its a flattened jelly roll. There's a video around here somewhere that shows a guy taking one apart and its a big flattened jelly roll with tabs spaced along it for the neg and pos terminals.I don't see how the jelly roll can be compressed.
I saw that video. There are also x-rays of jelly rolls. Still...I do not understand how it's possible to compress the jelly roll without crushing the aluminum case it's housed in, and I will add the cell is at a 0 SOC. I guess it would be possible if the cell has expanded and then some compression is applied to it?Because it's not cylindrical, its a flattened jelly roll. There's a video around here somewhere that shows a guy taking one apart and its a big flattened jelly roll with tabs spaced along it for the neg and pos terminals.
The upshot of all this is that yes, both pouch and flattened jelly rolls can be compressed. Whether they need to or not is up to the manufacturer to specify.
The second change is the cell thickness increase from BoL (beginning of life) to EoL (end of life). This change is typically not reversible. This irreversible thickness increase of the cell is gradual and happens over repetitive charge and discharge cycles... If the cells are restricted more than optimal, the capacity fade occurs faster and at the same time, it can be detrimental