Deep Discharge of LI Ion LMO Cells

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Jun 18, 2016
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HI all

I have a Vectrix VX1 with second gen Nissan leaf cells. Unfortunately, the BMS froze and dragged them down to a very low voltage (pack measures at 40 volts now instead of 150 volts).

I can revive these batteries by slowly charging cells groups at 500ma and monitoring the voltage rise/drop to ensure they are not running away, but is this safe?

They pack is worth £3k and would be a shame to chuck it all away. Thoughts?
 
Alexanderfoti said:
I can revive these batteries by slowly charging cells groups at 500ma and monitoring the voltage rise/drop to ensure they are not running away, but is this safe?
Not really. Any time you take voltages much below 2v per cell it's not going to be very recoverable. You could use them in applications where you aren't too worried about fire and/or reduced capacity (outdoor power source?)
 
It depends... I saw a lot cells of different chemistries (NMC, NCA, LFP) discharged below 1V and after recovery they served well like nothing was happened. The most problematic in this case was LCO cells (aka LIPO). So you have these options:

1) throw the battery in the trash
2) try to recover the cells/battery and then monitor if:
- cells are holding charge/voltage for longer period with no load applied
- cells are holding charge/voltage with load applied without significant disbalance
Ïf the battery pass this test, then there is significant chance that your battery will work for some more time. Of course It would be wise to monitor ideally each charging process. If not, then proceed to point 1)
 
Thanks all

Some cells are at 2+ volts, and I suspect those would be OK.

Most of the other are at 0.4-0.6volts (due to the way the balancer draws its power) its a bit of a pain!

I may drag it out of the garage, to somehwere more safe and see how it goes.

Some interesting reading here:

https://www.researchgate.net/publication/317934082_Effect_of_overdischarge_overlithiation_on_electrochemical_properties_of_LiMn2O4_samples_of_different_origin#read-preview
 
Is the manufacturer datasheet available? They may specify in that (eg murata vtc series do)
 
Under 1.0v-1.8v? No.

Above 2v, maybe.

Above 2.5v, yeah probably recharge slowly and the capacity will stick and it will nothave lost much.

I reccomend looking inside a module and seeing if the cells themselves are puffed and creating pressure. A puffed cell is a goner .
 
All the cells are clamped together so hard to see which is puffed without dismantling the pack. In the end I scrapped all the cells (££) not worth the risk.
 
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