It charges in 2 Hr up-to 4.5 V but sudden potential drop up to 1.5 V during discharge process.
Hi Saurabh,
Does the cell maintain a high voltage after the charge step? Leave the cell to equilibrate after the charge and monitor its potential, if it drops there may be some internal short.
Best,
Arman
Hello,
Normally, sudden potential drops at the beginning and at the end of the discharge process attribute to ohmic and concentration polarizations, respectively.
Hi,
The sudden potential drop after charging is due to ESR (equivalent series resistance) of the cell. This ESR includes the electrodes' interfacial resistance, electrolyte and membrane resistance to charge transport. Also, this drop is related to discharge C-rate. In simple words, the slow discharge would allow sufficient time to ionic species to migrate/diffuse upon reversal of the electrochemical reactions responsible for faradaic capacitive behavior. Therefore, the slow discharge could significantly decrease the potential drop. But the IR drop at the slow discharge is also associated with the cell design and can be reduced by adopting effective cell design strategies. I hope this answer suffices your question. Thank you
This sudden potential drop (during discharging in Li ion battery) is temporal (
Hello everybody,
Does anybody knows why sometimes during first discharging of battery, the sudden potential drop can b happened?
After 2-3 times of charging-discharging, sometimes it disappears but sometimes it remains.
Thank you in advance,
Dear Fahimeh Amiri ,
since there are so many reasons for this symptom[1] in (real laboratory) cells, then say, please,
1) what is your specific cell (case), and
2) show, if possible, a real time graph having the sudden potential drop(s).
1. Quotation (from Fahimeh Amiri): "Does anybody knows why sometimes during first discharging of battery, the sudden potential drop can be happened ?
After 2-3 times of charging-discharging, sometimes it disappears but sometimes it remains."
Dear Ioannis Samaras
First of all thank you so much for your time. Regards your questions i would like to add:
1) It's NIMH battery pack,
2) Here in attach please find some graphs that show the problem.
Regards,
Dear Fahimeh Amiri,
some cells, only one[1] cell (1.2V) in your case, of your pack(s) has a bit less capacity than it’s rated for. This weak (quasi-"bad"[2]) cell has less capacity and it would become empty before the other cells, upon discharging phase.
1. The sudden potential drop has a 'quantum (character) value', one cell value (1.2V).
2. You can locate a "bad" cell (and replace it), since it has the lowest Voltage (near zero), when your pack is near to the maximum of the SOC. Also, the "bad" cell is more warm.
Dear Ioannis Samaras
If it's one cell which doesn't work correctly, please let me know why:
- In some packs by doing second test (second Charge-Discharge) , there is not this drop?
- why the capacity of total pack works correctly?
- Regards,
This (quasi-"bad") cell, having initially less (dC, only 1 to 5%) capacity, might recover[1] the initial capacity loss dC by its' shelf warming[2] process at the 1st cycle.
Also, the nominal rated capacity (see the pack's specs) has always a standard deviation near to 5% among their manufacturer's part numbers (sometimes up to 10% or even more) depending on the brand name, as well as the local market(ing) laws (or regulations).
1. There are many scenarios for such a composite electrodes' initial instability.
2. The ("bad") cell's internal resistance (impedance) increases a lot, after discharging more than its actual rated cells' capacity.
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