My 2 cents:
We all know the recommendation:
300kgf compression force.
It supposed to give even 1000 extra cycles, for what those numbers are worth anything.
I know from my own experience that it highly dependent on the cell.
I have 48* 152Ah, in March my Idea was bigger is better..
First indent was the 120Ah cells.
These where a fraction more expensive and same casing size......
- that matter a lot.
You can not keep on piling sheets into a casing without getting in the danger zone..
They needed to be compressed, if not they will bloat / delaminate.
My 280Ah came a few months after the 152's, and together they have made up 736Ah battery.
It never was overcharged, never undercharged, kept between 15 and 85%.
After 150 days I'm ready to make my new Powerwall installation...
150 days ago most of the 152Ah where still flat.
I ordered 3 replacement as I knew 3 where starting to bloat a little.
All the 152Ah are bloated / delaminated.
And all about the same.
They have 1.25mm (in total 2.5) bloating.
The 280??
0.0 mm, no bloating at all.
I'm in day 4 of building the new Powerwall.
When finished I'll post the progress.
Then this thread popped up again..
I could not let it pass to show what not compressing can have for result.
I have no idea how much capacity I lost due the delaminating.
Perhaps I'll test some day one to know for sure.
I guess 10% or less.
Should you compress???
Absolutely.
Even if your cells are not "overfilled" like mine, it still won't hurt to compress them
And allowing expansion??
That would be stupid.
The cells are make of sheets LiFePO4.
Once they get space between them, it doesn't revert.
It's not a balloon...
You can't "de-bloat" or re-compress cells.
There is air inside what we all know is really good comprassable.
If the sheets need to expand due to temperature difference, it can do within the housing.
Sure, you should not smash the cells.
Too much of everything is bad.
Allowing space between the cells for expansion...
Look at my lovely 152Ah...
That is what will happen.
Without over charging, without undercharged, without too high C rates.
On average C0.1..max C0.2