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how do you think about EV and lifep04 battery suppliers in China?Are their technology reached maturity level?
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how do you think about EV and lifep04 battery suppliers in China?Are their technology reached maturity level?
I would say Chinese LFP cells are of decent quality, but not great - one thing that definitely needs improvement is the rigidity of the cell casings. The cells tend to swell during heavy use, especially in hot climates and all of the manufacturers require the use of metal plates and straps to restrain this swelling. Unfortunately, having to keep the cells bundled up with the manufacturer's strapping makes it a lot harder to find spots to install them in a vehicle. The end user has no choice but to break the bundles apart and then figure out how to repackage them so they won't swell. This, to me, is totally unacceptable because once the cells start to swell a vicious cycle ensues: the internal resistance increases rapidly with swelling which causes the cells to heat up more which causes more swelling, etc.

Additionally, the datasheets for all of the Chinese LFP cell manufacturers are poor. Some don't even include good dimensional data and even worse is that the manufacturers often change the dimensions of the cells without warning or even updating the datasheet (if it had dimensional data in the first place).

Internal resistance of the cells, even those in the same "batch", can vary wildly. I have personally found a 2:1 variation in cells by recording the difference in voltage drop when rapidly switching back and forth between a 1C and 2C load.

One good thing I will say is that cell capacity (in Amp-Hours) is almost always accurate.

Overall, it does appear that Chinese LFP cells are improving and that bodes well for the future.

It would definitely be nice if they were more widely available in the US.
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If they did that, the cells would be larger and heavier, and you'd be complaining about their poor energy density.
Please don't presume to know what I will complain about. :D

I am sorry, but I believe there is a big misunderstanding. The swelling is NOT heat related! And it is independent of cell resistance. The swelling is SOC level related.
- 0 ~ 90 % SOC = not swollen, regardless of usage.
- ~100 % SOC = swollen, whether sitting on a shelf, charging, or discharging (at any current, and for any cell resistance)
That doesn't precisely match what I have observed, Davide, but I won't claim to have exhaustive knowledge or to have made a statistically significant number of observations here, either.

That is to say, I have drained an old style TS 200Ah cell to 0V at a rate of 0.1C and left it there overnight and though it did swell slightly, it was not to near the extent of ones that got that way when in EV service. I suspect that the truth may prove to be that going below 10% SoC while pulling high amps is the real cause of swelling.

However, if swelling only occurs when SoC gets critically low then I agree that a stronger case is not necessary.
I apologize. I must have misread when you said "... one thing that definitely needs improvement is the rigidity of the cell casings. ... This, to me, is totally unacceptable ..."
Oh no, you read that right. I was saying to not presume what I might complain about next... ;)


Did you do it on purpose or was it an accident? Bringing a TS cell below 2 V damages it severely.
Sort of both... I was testing cells for capacity, internal resistance and temperature sensitivity to help the Soliton1 deal with their peculiarities better. This particular cell - that I picked at random from a batch Rebirth Auto ordered for a conversion (they wisely bought 5 extra cells) - had about 190Ah of capacity whereas the others had closer to 210. I expected it to take more than 10 hours to fully discharge but it only took less (I guess about 9.75). As you probably know, discharging a cell for just 1 minute too long is more than enough to kick it's voltage into the dirt...

The cell did charge back up just fine at 40A and absorbed ~195Ah which it then delivered again without complaint. I have not gotten around to seeing whether the internal resistance has changed, and I cheerfully admit this is but one data point, but so far it seems that the rate at which you discharge a cell has some effect on the amount of damage done.

I am not aware of a mechanism that would result in swelling of a cell that was brought down to 0 V (cells are never brought below 2.0 V)....
No offense - seriously - but I have not gotten the impression that anyone really knows what is going on inside a lithium-ion cell. There's more physical chemistry than electrochemistry at work here, it seems, (ie. - the black magic and voodoo zone of chemistry). I mean, the manufacturers themselves can't seem to agree on such basics as what the nominal voltage is, or what voltage to charge the cells to, etc...

Swelling occurs at full SOC (100 % = 4.0 V), not at empty (0% = 2.5 V)....
So you are saying that overcharging - or, more specifically, charging to exactly full - is what causes swelling?

That is definitely not what Rebirth Auto has experienced. Cells are fine before going on an endurance test drive; cells are swollen with some at 0V, even, upon returning to the shop. This is with the Soliton1 controller set to limit current when the pack voltage dropped to an average of 3.0V per cell, btw (once again arguing for the importance of a cell-level BMS, but I suspect you understand that quite well ;) )
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i do not mean that BMS and cooling is the same thing,i was wondering what is the product on the web

It's a 300V nominal, 1000A continuous DC motor controller.
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