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Is this a magic pot, or a self-healing Li-Ion battery?

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RoGeorge:
2 years later...  :)
For the curious, the voltage of the same 10Ah cell while sitting disconnected on a shelf since last recharged 628 days ago:




--- Code: ---Days Voltage
0.000 4.1873 2023-04-17
0.021 4.1813
0.208 4.1599
0.625 4.1390
3.000 4.1062
5.000 4.0935
19.000 4.0663 2023-05-06
34.000 4.0605 2023-05-21
52.000 4.0571 2023-06-08
99.000 4.0521 2023-07-25
562.000 4.0330 2024-10-30
628.000 4.0318 2025-01-04

--- End code ---

To recap the story, I've found this cell in the EE waste basket about 2 years ago, it was so bulged it was 2-3 times thicker than normal, and the solid body of the battery (under the gasses inside the plastic pouch) was somehow soft, like a putty, but I didn't insist pressing on it.

Then after charging to 4.2V, I've let it sit, and found it deflated a few days later.  In fact, judging by the external plastic pouch it was looking like there was some vacuum inside.  And the putty-like material inside became hard as a plank. Still is.

Would be interesting to measure the current mAh, just that I didn't do that two years ago, so can't appreciate if, or by how much, that bulging incident from 2 years ago affected the cell.  Now I have the SW and HW setup to measure the mAh while discharging a battery, just that I have to do that while sitting in the same room for about 10-20 hours (it's a raw cell, no protection whatsoever, with at least one bulging incident in the past, and of an unknown provenience, and has a lot of Li inside - 10Ah nominal).  Don't want to risk a fire by letting it to discharge unsupervised, not even for a minute.

Jeroen3:
You can discharge outdoors with a simple resistor if you intend te reycle it.

RoGeorge:
Discharged the battery already.  Put it in the same thick metal pot, with a lid, and discharged under a constant current of 1A while logging the I, V and T.  The battery didn't heat at all.

The surprise was to drain yesterday more than 6.4Ah out from that battery (stopped at 2.5V).
That is for a 10Ah battery last charged 20 months ago, when it was as bulged as a pillow!  :o

After discharging, put it to charge overnight, with 1A and top 4.2V.  Stopped from charging when the current dropped to 80mA.  About 9.1Ah were put into the battery during the last night charging.  Now it is discharging again under 1A (0.1C) constant load, and so far it looks like a battery in good condition.

(Topic moved note:  This topic started as a curiosity, but turned into a long term experiment, so moved it from 'General Technical Chat' to 'Projects, Designs, and Technical Stuff'.)

ArchieAltz:

--- Quote from: RoGeorge on January 06, 2025, 09:51:33 am ---Discharged the battery already.  Put it in the same thick metal pot, with a lid, and discharged under a constant current of 1A while logging the I, V and T.  The battery didn't heat at all.

The surprise was to drain yesterday more than 6.4Ah out from that battery (stopped at 2.5V).
That is for a 10Ah battery last charged 20 months ago, when it was as bulged as a pillow!  :o

After discharging, put it to charge overnight, with 1A and top 4.2V.  Stopped from charging when the current dropped to 80mA.  About 9.1Ah were put into the battery during the last night charging.  Now it is discharging again under 1A (0.1C) constant load, and so far it looks like a battery in good condition.

(Topic moved note:  This topic started as a curiosity, but turned into a long term experiment, so moved it from 'General Technical Chat' to 'Projects, Designs, and Technical Stuff'.)

--- End quote ---
Interesting how it didn't turn into a fireworks show during the discharging , seems like you got a magic pot on your hands  :-DD

RoGeorge:
Meanwhile, did 5 cycles of charging/discharging at 1A.

Depending on how much it was charged (the stop current at 4.2V), and depending on how much it was drained during discharge (first at 1A stopping at 2.5V, then wait for voltage to recover and drain some more current at less than 1A, but with the same Vmin=2.5V limit) measured about 7-8Ah.  Logged and plotted the I and V during charging/discharging.


Regarding the bulging, it didn't happen at the first charge/discharge cycles.  But at the last discharge, I've insisted to repeatedly drain the battery down to 2.5V, wait for it to recover, then drain again at a smaller current, and so on, until I've drained out almost as much energy as it was put in during the previous charging.

As an effect to over-discharging, at the end it was a layer of about 1mm of gas between the solid body of the battery and its plastic pouch (the solid body of the cell is about 10mm, factory packed in a plastic pouch).

Then recharged it all night (limited 2A and 4.2V max), and until the next morning the charging current dropped to only 6mA, and the 1mm of gas was gone.

The battery looks again like there is some vacuum inside its plastic pouch.  My best guess so far is that somehow, this battery produces gases when discharged too much, and can absorb back the gasses into its solid body during charging.


P.S.
All these charge/discharge cycles were made inside the same container, so the magic pot theory is not yet disproved.  ;D

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