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Don't keep fully charged Li-Ion in long term storage, they tend to bulge
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SiliconWizard:

--- Quote from: MadScientist on January 17, 2023, 05:38:37 pm ---Very low charge rates should be avoided , ie below 0.2 C as  very low  charging rates encourages SEI layer growth and hence leads to battery degradation.  Chargers at 0.5c then stop charging once full no float etc needed. Track SOC band restart charging at a point

--- End quote ---

In my experience mentioned earlier, a combination of a 0.1C charge current and automatically recharging the battery, keeping it at 100% most of the time, was a sure recipe for dangerous bulging and killing the batteries.

Thus, any UPS system based on Li-ion batteries should definitely be designed appropriately, and there's little surprise lead-acid batteries are still popular in UPSs.
thm_w:

--- Quote from: MadScientist on January 17, 2023, 05:38:37 pm ---Very low charge rates should be avoided , ie below 0.2 C as  very low  charging rates encourages SEI layer growth and hence leads to battery degradation.  Chargers at 0.5c then stop charging once full no float etc needed. Track SOC band restart charging at a point

Long term storage is best at 60-70 % SOC but really fine upto 80% SOC avoid very low Soc for storage or below 40% SOC

In essence short high current charge ( relatively high ) is best once the correct safety regime and a proper stop charge point is set

--- End quote ---

Citation? What I'm reading shows the opposite.
And any any sort of cycle life studies all get better as charge rate decreases, down to 0.2C or 0.1C, is about the lowest. I don't see any studies lower than that.

"Temperature rise due to reaction and joule heating accelerates the SEI layer growth and causes more capacity loss" https://iopscience.iop.org/article/10.1149/06127.0043ecst

This might be relevant to what you are talking about though: "The kinetically limited expressions from equations 2 and 3 are qualitatively similar, with both showing much greater SEI growth during the later stages of charging, especially the CV portion of charging. "
https://iopscience.iop.org/article/10.1149/2.1161412jes
MadScientist:
The studies are there if you Google them. Trickle charging has never been recommended for li ie very low fractions of C

Li performs best if the charge cycle is as short as practical consistent with safety and battery max specs
tom66:
0.1-0.2C charging rate would be about normal for an EV battery (~60kWh pack, 7kW AC charger), yet the data shows that rapid charging (while the effect is not hugely significant) is definitely more damaging to the cells than slow charging.  So I'm not sure I accept the SEI layer buildup stuff.
thm_w:

--- Quote from: MadScientist on January 17, 2023, 11:11:05 pm ---The studies are there if you Google them. Trickle charging has never been recommended for li ie very low fractions of C

Li performs best if the charge cycle is as short as practical consistent with safety and battery max specs

--- End quote ---

rightttt so its on me to find the proof of your claim, which contests with existing studies.
Lower charge rates results in longer cycle life, down to 0.2C or lower.

https://www.researchgate.net/figure/Capacity-development-vs-equivalent-full-cycles-depending-on-the-charging-rate-of_fig4_286242928
https://www.sciencedirect.com/science/article/abs/pii/S0378775318310462
https://pubs.rsc.org/en/content/articlelanding/2018/ra/c8ra04074e (LiFePO4)
https://www.osti.gov/servlets/purl/1397110 (some C/10 cycle tests)
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