Compression analysis for various configurations

[Checkthisout]

At full SoC the graphite expansion will cause about 1-2 mm thickness expansion of a 280 AH cell. Doesn't sound significant until you consider the total summation of 16 cells arranged in a single row being over half an inch end to end.

What do you suggest as a holding fixture, if any

 

[Skypower]

I’m thinking there’s now at least three schools of thought on this, freestanding, fixed compressed and spring compressed.

 

[Warpspeed]

I’m thinking there’s now at least three schools of thought on this, freestanding, fixed compressed and spring compressed.

So it would seem.
As most of our cells come from China, there is also the Chingrish translation problem.
Its very easy to laugh, but how many of us here could write a serious battery installation procedure in Mandarin Chinese without creating howls of laughter and total confusion in China ?

 

[JoanTheSpark]

[..] But this begs the question, in an extreme condition, what kind of pressure are the cells exposed to in a lightly snugged up rigid fixture when the cell are known to expand? I haven’t got a clue.

What about CYLINDRICAL cells where the pressure has no means to "enlarge" the cell canister in any meaningful way.
Per the logic of "cells need space to expand into when going from SOC 0%-100%" those type of batteries would be trashed constantly and have a very short life.. but as afar as I know in the real world every major BEV maker is now switching over to cylindrical cells instead of pouch/prismatic cells.
Cylindrical cells have no means of expanding - the internal pressure in them IMHO is not being moderated at all.

 

[JoanTheSpark]

But I have had success clamping bloated cells back to the original shape, which they then maintained.
Those cells are still working perfectly well years later.

Thanks for this info. I have here some prismatic cells (50Ah) laser welded together at the top (bought like that as a 12V100Ah battery) with some bloating.. reading that it's possible to get them back into shape (carefully) successfully gives me hope I can do that.

 

[Warpspeed]

My cells were the 50Ah Winston cells with the yellow plastic case.
I clamped them flat within a few hours of the bloating accident, and they fully recovered and are still working fine.
That may not work with very old bloated cells ?
I really do not know.

 

[JoanTheSpark]

My cells were the 50Ah Winston cells with the yellow plastic case. I clamped them flat within a few hours of the bloating accident, and they fully recovered and are still working fine. [..]

The ones I got are the modern alu-can type and from Feb/2021 (laser welded at the top) . See attached picture (blurry in the hurry) to get an idea. They behave normal, but I don't want to keep cycling them with this strain on the terminals and the internal electrolyte level being questionable. So I'm going to try to compress them back into their square style (carefully).

My biggest fear is popping the pressure relief valve by doing this, which is why I ask about this here:

Do LFP battery "pressure relief valves" reseal on their own?

As per title I was wondering if the pressure relief valves on those cells reseal themselves after they have released the pressure or if they break and that is it (they never seal again)? Thanks.

diysolarforum.com

 

[Warpspeed]

So I'm going to try to compress them back into their square style (carefully).

Definitely worth a try.