Charging lithium batteries that sat for 2 years

[telgareith]

Circumstances forced me to leave: 4 Eve 105Ah LiFePO4/LFP prismatic, 32 27??? LiFePO4 cylindrical, and 80ish Samsung 25R 18650 cells on a shelf for 2-3 years. All were 50-70% charged at that time. I've finally gotten access to them again, but every one I've touched so far charges slowly. For example: the Eve 105Ah are charging at 6 watts @ 3.6v with a bench supply, but the spec sheet says 15 mOhm internal resistance.

Are they all garbage now, or am I forgetting something?

 

[sunshine_eggo]

Circumstances forced me to leave: 4 Eve 105Ah LiFePO4/LFP prismatic, 32 27??? LiFePO4 cylindrical, and 80ish Samsung 25R 18650 cells on a shelf for 2-3 years. All were 50-70% charged at that time. I've finally gotten access to them again, but every one I've touched so far charges slowly. For example: the Eve 105Ah are charging at 6 watts @ 3.6v with a bench supply, but the spec sheet says 15 mOhm internal resistance.

Are they all garbage now, or am I forgetting something?

Batteries or cells?

It sounds like you meant cells.

What was the voltage of the 4 EVE cells when removed from storage?

Did you fabricate high quality leads with ring terminals, or are you using the bullet connectors and alligator clips? If the latter, you have mega resistance in the connection between the supply and the cells.

When the power supply measures 3.6V, what do the cell terminals measure with a voltmeter?

 

[MattiFin]

When the power supply measures 3.6V, what do the cell terminals measure with a voltmeter?

You beat me to it. My thoughts exactly.

 

[RCinFLA]

What was the cell open circuit voltage as you found them is most important. If were less than 1.5vdc they likely have grown lithium metal dendrite shorts. If less than 2vdc always start with low charge current until cell gets above 3vdc. If they have dendrite shorts and you force too much charging current the cell can overheat and burst. If the cell voltage doesn't rise with the low (<0.05C) charge rate it means you have significant cell dendrite shorting and cells are bad.

If you have good wiring connections and cell quickly rose to 3.6v then you likely have dried out electrolyte. Likely due to cell bloating pressure popping top vent port from excessive low SoC cell voltage (<1v).

Cells can have 0.5% to 6% of rated capacity per month of self-discharge depending on condition of cell and ambient temp they are stored at. High ambient temp causes greater self-discharge rate.

 

[telgareith]

Thanks everyone. I forgot to verify voltage at the cell's terminals.... which would have lead me to find out I didn't make my power supply leads as chonky as I thought.

I'm charging my third battery today using XT60 to ring terminals with 12awg stranded Silicone(Just for the temp rating). Alas this charger can only do 20 amps at <=3.6v Or, I might need 8 or 10awg... but 21A is good enough for me.


Also- They all show as above cutoff voltage aka 0% SOC.

Thanks!