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Cell storage
#11
(06-09-2019, 02:45 PM)BlueSwordM Wrote: The commonly accepted practices exist mostly for shipping and usual storage.

We want to keep our cells as healthy as possible, so a lower voltage is beneficial.

Do you know the scientific reason why? Everything I have seen restricts depth of discharge to like 30% or so, but what we have seen is that low voltage is actually good for the cells when talking about storage.

Oh and lucky find, kc8adu!
Formerly known as Dallski
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#12
yes that was a dumb luck find.
came to the auction for the spare cnc controls i knew they had and got their cache of new laptop packs they never used and left sit in the supply room.
i have found that <50% charged and low as possible temp short of freezing is best for shelf life.
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#13
@Dallski, there are 2 factors that hurt lithium ion's cell capacity over time.

1. Temperature.
2. Storage voltage.

Since lithium ion cells are chemical batteries, the main 2 factors affecting storage capacity are the ones noted above.

Higher temperature means parasitic reactions occur faster.
Higher voltages means more of these parasitic reactions can occur(ions passing through the separator, a semi-permeable membrane), and self-discharge, and capacity loss, is higher over time.

The main reason for keeping around 30% charge is so that you can actually use them. At 10% charge when in storage(3,3-3,5V), it's almost nothing.

The lower the initial storing voltage, the lower the actual self-discharge, and the lower the damage to the cell.

That's why storing cells at full voltage isn't a good idea. The voltage may go down over time, but you may permanently lose capacity, and it'll lose voltage more rapidly compared to the other one, and if left for long enough, can go down in voltage further than a 3,4-3,5V stored cell.
100kwh-hunter likes this post
The power of lithium ion is in our hands!
We'll show them what we're made of!
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#14
Thanks for the explanation. So apparently, according to Paul Voelker's research as cited by Wikipedia, storing at >3.6V initiates electrolyte oxidation and induces SEI layer formation, while storing at less than 2V degrades the cathode and releases oxygen.

So there you have it. Store cells between 2V and 3.6V for best results.
Formerly known as Dallski
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#15
Not adding anything new to the discussion beyond some links to additional reading:
https://batterybro.com/blogs/18650-whole...s-die-long
https://batterybro.com/blogs/18650-whole...ies-safely

I found the same info that Dallski did.  Currently only discharging to 3.7V because that's what I can manage with the my Opus.
Mobilis in Mobili

Cell count as of 7/19/2019
54 Cells >2000mAh, >80% Rem. Cap., 14 day resting voltage >2.12V
100 Cells of Everything Else

Aiming for 2400 tested cells a year with one charger
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#16
Great read!
I had to read the papers twice to fully understand.
It explains a lot why and how to storage at a certain voltage.
So i will stick with my 3.45 volts.

Thanks all
Still learning English. Learning Li ion and solar technology.

1400 cells in packs Exclamation above 2500mah and 90%soh.
~400 cells between 1800-2500 and above 90%soh(sell?)
600 cells between 2200 - 3000mah, 80-90%soh (sell?)
2600 waiting for testing.
approx: 500 cells not safe for use: dead, heaters, to high ir or sd

Time is our enemy, must work to, the sun is our friend, must relax to.
With best regards
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