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Don't keep fully charged Li-Ion in long term storage, they tend to bulge
Siwastaja:
I can use whatever arguments I want :).
I'm not talking about "top tier" cells. I'm saying if a cell dies on its own due to self-discharge bringing it from 30% to zero, it's total crap. Possibly dangerous. Use at your own risk, and if weird tricks are needed to keep it "alive", this information is not useful to generalize.
Besides, charging it to 70% won't help. If it self-discharges that much at 30%, it self-discharges even more at 70%, so it gets to 30% and then 0% quickly anyway. You would need to keep the cell in a charger all the time, and that would make it even more dangerous.
Now a broken-by-design protection module could be nearly constant current drain, so using e.g. 80% instead of 40% would double the "time-to-death". I still don't know if it's worth anything. 30% is massive amount of charge to lose. Trying to work around a protection module which loses 3% per month is like using duct tape to keep your steering wheel from falling off in a car. (mandatory car analogy). Or use bubble gum to fix a hole in gasoline tank, I did that once in my car and guess what, I had to repair it properly the next day anyway.
magic:
Is there any "quick and dirty" way to put a battery into a reasonably safe long term storage level without coulomb counting?
Like, say, (dis)charge to 3.6V or 3.8V or something of that sort.
Siwastaja:
--- Quote from: magic on January 15, 2023, 12:03:01 pm ---Is there any "quick and dirty" way to put a battery into a reasonably safe long term storage level without coulomb counting?
Like, say, (dis)charge to 3.6V or 3.8V or something of that sort.
--- End quote ---
Anything between about 3.55V and 3.7V is nearly optimal. 3.8V is fine, too, but don't go much over that or you'll start losing the advantages in calendar fading. People assume storing at 4.0V is already significantly better than at 4.2V, but depending on cell, the difference can be small.
Remember, if you use large discharge current, terminal voltage = OCV + ESR * I, where OCV = open circuit voltage, which you try to get within your optimum range. So, maybe simply discharge down to say 3.55V and let the voltage bounce back to 3.6V or 3.7V or whatever; it's good enough.
BravoV:
Alternative view, on storing Li-Ion cell, the sweet spot is 4.03 volt, the longer the cell is soaked in higher voltage, say like 4.15 volt, the faster the decay.
At least according to Jeff Dahn at below video is at 4.03 volt ... approx. about 80%, and gets worst above 4.1 volt. He is well known expert in battery, currently working with Tesla in battery development.
You can search who Jeff Dahn is, in the net.
I marked youtube link below right at the time at 1h07m, in this Youtube video where its discussed this particular issue ...
-> https://youtu.be/pxP0Cu00sZs?t=1h7m5s
Even though its a 1 hour 14 mins video length, recommending to watch this Prof. Jeff Dahn video from the beginning, its very informative, imo.
Siwastaja:
--- Quote from: BravoV on January 15, 2023, 01:18:07 pm ---Alternative view, on storing Li-Ion cell, the sweet spot is 4.03 volt, the longer the cell is soaked in higher voltage, say like 4.15 volt, the faster the decay.
--- End quote ---
As always, "alternative views" tend to be wrong.
You can refer to the measured data on Samsung 29E cell posted by me for example in this thread:
https://www.eevblog.com/forum/chat/lithium-ion-battery-degeneration/msg3217888/#msg3217888
I also remember a paper where a Panasonic cell faded MORE quickly at around 4.0V than fully charged. I haven't replicated this of course and don't remember the authors/title.
But sure, some particular cell type, possibly something used at Tesla, can already show calendar fading down to negligible values at 4.03V, and it's obviously a pretty good feature for a cell. For example, in my dataset of two cells, one (Samsung 26H) was that way. Just don't generalize it and assume all cells show significant calendar life improvements at 4.0V.
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