As the title says what causes a soft or 'loose' pouch cell? These are new cells that I suspect are OEM rejects. Some minor foil damage here and there as expected but something that caught me off guard is soft pouches were the jelly roll is not rigid. There doesn't seem to be any puffing at all, the pouch seems to be relatively well formed but otherwise it is soft. Anyone shed some light on what exactly went wrong or is causing this in what is otherwise a new unused cell? I'm use to cells being quite firm and solid when tapped.
Soft bodied pouch cells. Too much electrolyte?
- Thread starter Mugenski
- Start date
There's probably gas in there, perhaps even between the layers, even if it's not "swollen". Same causes, just not as bad yet.
If you test them and find their internal resistance is not perfectly matched between cells, or is not at the value the manufacturer spec sheet indicates, then that's a bad sign probably indicating this is the problem.
If you test them and find their internal resistance is not perfectly matched between cells, or is not at the value the manufacturer spec sheet indicates, then that's a bad sign probably indicating this is the problem.
Thanks AW. Kicker here is my 1035+ doesn't show anything suspicious when looking at OCV or resistance. Tested capacity is slightly lower on the softer cells, about 1% less the mean of all cells. Capacity RSD is .56% and OCV RSD is .015% which I feel is good. That said load testing is the only way I'll know for sure.
Supplier is telling me the cells will firm up when charged. When pigs fly.
Supplier is telling me the cells will firm up when charged. When pigs fly.
RSD? I am drawing a blank as to what this refers to
Later floyd
If they "firm up" it means they're outgassing; that's the only thing that could do that. 
(FWIW, all pouch or prismatic cells require compression to correclty operate; the manufacturer spec sheet should call out what pressure that should be).
If the cells were truly "good" they'd be identical in characteristics. If RSD is Relative Standard Deviation, or what the worst case difference is between them, and 0.015% is the "average" difference between them, I guess that's pretty close to identical.
But the fact that the softer cells specifically are different from the others indicates a phyisical and electrical correlation--that there *is* a physical problem with them causing an electrical difference. That sort of thing usually gets worse with time.
I have decade-and-a-half-old EIG NMC cells that even now that their capacity and internal resistance has degraded significantly from aging, are still the *same* as each other--they still stay equal in voltage (within a flickering hundredth of a volt on a Fluke 77-IIIA) when charged or discharged, and I've never used a BMS or balancer on them, on any of the three 14s2p packs.
I don't have any test equipment for cell Ri, but the Cycle Analyst has an estimate of total pack resistance I could check to see what it presently thinks they are, and I've noted a few times over the years what it saw them as in the SB Cruiser thread, to see how they evolved over the years...but it's just an estimate, and only for the whole pack.
(FWIW, all pouch or prismatic cells require compression to correclty operate; the manufacturer spec sheet should call out what pressure that should be).If the cells were truly "good" they'd be identical in characteristics. If RSD is Relative Standard Deviation, or what the worst case difference is between them, and 0.015% is the "average" difference between them, I guess that's pretty close to identical.
But the fact that the softer cells specifically are different from the others indicates a phyisical and electrical correlation--that there *is* a physical problem with them causing an electrical difference. That sort of thing usually gets worse with time.
I have decade-and-a-half-old EIG NMC cells that even now that their capacity and internal resistance has degraded significantly from aging, are still the *same* as each other--they still stay equal in voltage (within a flickering hundredth of a volt on a Fluke 77-IIIA) when charged or discharged, and I've never used a BMS or balancer on them, on any of the three 14s2p packs.
I don't have any test equipment for cell Ri, but the Cycle Analyst has an estimate of total pack resistance I could check to see what it presently thinks they are, and I've noted a few times over the years what it saw them as in the SB Cruiser thread, to see how they evolved over the years...but it's just an estimate, and only for the whole pack.
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Regarding Ri measurement devices. I find it difficult even with the 1035+ to get a wholly consistent number in the milliohm range. Noticed that it seems like after the devices runs for a time it will drift upward slightly. Likely from the heat associated with using it.If they "firm up" it means they're outgassing; that's the only thing that could do that.
If the cells were truly "good" they'd be identical in characteristics. If RSD is Relative Standard Deviation, or what the worst case difference is between them, and 0.015% is the "average" difference between them, I guess that's pretty close to identical.
But the fact that the softer cells specifically are different from the others indicates a phyisical and electrical correlation--that there *is* a physical problem with them causing an electrical difference. That sort of thing usually gets worse with time.
I have decade-and-a-half-old EIG NMC cells that even now that their capacity and internal resistance has degraded significantly from aging, are still the *same* as each other--they still stay equal in voltage (within a flickering hundredth of a volt on a Fluke 77-IIIA) when charged or discharged, and I've never used a BMS or balancer on them, on any of the three 14s2p packs.
I don't have any test equipment for cell Ri, but the Cycle Analyst has an estimate of total pack resistance I could check to see what it presently thinks they are, and I've noted a few times over the years what it saw them as in the SB Cruiser thread, to see how they evolved over the years...but it's just an estimate, and only for the whole pack.
I think I am going to use OCV and cell capacity as a metric for which cells get paired together. Taking it a step further there was a professor by the name of Billy Wu I came across on YT that stated the weakest cells location in a highly parallel pack assembly was a relevant factor to the capability of the battery. This is likely well understood by many here already. It's less helpful for me with a 2P pack but I think it's good knowledge to share.
I'm also regretting laser welded tabs on my cells as I've decided to go with a punch and clamp connection method. Hindsight it may have been best to request that the stock cell tabs weren't cut off when the more readily solder-able tabs were added.
Hillhater
100 TW
DC iR is easy to measure at cell level using just a MM, an Ampmeter, and a suitable load.
Just measure the difference in voltages under one or two load levels, recording the different amps, then use Mr Ohms law to determine the iR !
there are several threads on ES that detail the process if necessary.
Just measure the difference in voltages under one or two load levels, recording the different amps, then use Mr Ohms law to determine the iR !
there are several threads on ES that detail the process if necessary.
I think this may be part of the issue with the 4 wire tester I have. Likely can't load the cell enough to get a good reading on it. Seems to fluctuate or perhaps I am just splitting hairs.
I should tear a space heater apart and put a good load on the cell. At least a few hundred watts.
