Cell compression?

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jonescg
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Cell compression?

Post by jonescg » Wed, 14 Nov 2018, 14:36

Some recently published research on the impact of cell compression on charge retention and internal resistance.
226 Effect of compression on Li Ion cells.pdf
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Conclusion: Some compression is good, but it's possible to overdo it. 1.4 MPa was ideal in this instance.
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Re: Cell compression?

Post by weber » Wed, 14 Nov 2018, 19:34

I don't think anyone is in danger of overcompressing their cells. That's an insane amount of pressure. It's 14 atmospheres! For the cells in Mexy, whose broad face is approx 0.12 m x 0.18 m, it's equivalent to a weight of 3 tonnes!
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Re: Cell compression?

Post by jonescg » Wed, 14 Nov 2018, 20:06

Yes the equivalent of 14 kg per square centimetre, or about 1 ton per pouch cell :o
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Re: Cell compression?

Post by francisco.shi » Wed, 14 Nov 2018, 23:15

And I was worried I was compressing my cells too much. I applied enough pressure to bring the cell to the thickness specified in the specs. But I think the force I am applying is nowhere near what they say is optimum.

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Re: Cell compression?

Post by jonescg » Thu, 15 Nov 2018, 06:38

I have pouch cell stacks which aren't compressed still working well with a few lines of Kapton tape. I think your efforts will be fine.
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Re: Cell compression?

Post by weber » Thu, 15 Nov 2018, 06:54

I can't help wondering if the authors are confusing megapascals with kilopascals. The strange numbers they are using, like 1.32, suggest they were working in non-SI units. Edit: But I can't find any units that would give round numbers for pressure. Nor can I find any that would give round numbers for force on their 30 mm dia cells.
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Re: Cell compression?

Post by francisco.shi » Thu, 15 Nov 2018, 07:39

I remember reading somewhere that they were using 10psi of pressure which sounds more reasonable.

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Re: Cell compression?

Post by Richo » Thu, 15 Nov 2018, 12:42

Even if it was atm that is still 300kg on Mexy's broad face.

Still they are only 10mAh "home made" batteries.
And where is the control (no pressure)?

Given the conditions what they are seeing may not be transferable into the real world of pack building.
If they were then they would use commonly available production cells from the same batch in a large sample size.
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