I have a 10S 36 - 42 V LIPO battery with all cells puffed due to prolonged not being used. I recharged the cells one by one 4.2V max under CC/CV conditions and they regained their normal format. The puffing disappeared. I would like to know more about the process that caused the puffing and return to normal. I can not find adequate info on the internet
A properly designed Li-ion pouch cell, charged within the specified limits will not puff out. Puffing out is an indication of overcharging and/or poor cell design.
The pressure in a pouch Li-ion cell is due to the state of charge, not due to the act of charging. When the state of charge drops below 100 %, the pressure drops, and the pouch Li-ion cell recovers somewhat.
I say "somewhat" because a Li-ion pouch cell is permanently degraded if allowed to puff out, due to delamination of its layers. The proper way to build a pouch battery is to place the cells within a mechanical restraint with a bit of resilience to contain the pressure and prevent expansion.
And I say "Li-ion pouch cell" because "LiPo" is a widely used misnomer. The chemistry is "Li-ion", not "LiPo", and the format is "pouch", not "LiPo". A cell with a Lithium Polymer separator was developed, yes, but it never left the lab. Later, vendors co-opted the term when selling Li-ion pouch cells. Indeed, the chemistry in most pouch cells is the same as in the typical 18650 cell: LCO (Cobalt). And the technology inside it is the same as in a prismatic cell: a flat roll.