I am developing a battery using LFP-type cells. It is composed of 23 cells and a BMS. During testing, we have found that cell number 1 (Negative pole) discharges much faster than the others. Perhaps someone could provide a technical explanation for this phenomenon? I appreciate your attention in advance.
It would be better if you could provide your fabrication procedure. Based on that, we may give you some comments
Hello, The cells generally won't have the exact same capacity even if they have been made with the same procedure, one case can be during the coating of the material on the current collector, if the flow of the material is irregular and/or the current collector is not well stretched or oscillates during the coating, it will surely lead to variability in the thickness and uniformity of the electrode coatings and so a difference in capacities of the cells. This difference will be more or less depending on the severity of those phenomena, especially is the machines are not calibrated well periodically.
Now if these effects were minimal in comparison with what you measured, other factors like storage may have caused some electrolyte leakage.
Now if you wanna solve the problem, avoid using that cell with the others, especially if they are in series. Batteries mounted in series should have the same capacity and should start at the same state of charge, Batteries mounted in parallel should start at the same voltage.
Please beware that this is very important as Lithium ion batteries have risks of overheating, damage or explosion in case they are overcharged or not well mounted together.
Hi An-Giang Nguyen, thank you for your answer. The battery is composed of cylindrical cells of 3.2V6Ah (LiFePO4 type), and the configuration is 23S36P using copper plates. The BMS measures the voltage of each cell, as well as the discharge current.
Taking into account that the 23 modules are connected in series to achieve 73.6V between poles, I have found that cell number 1, from which the negative pole originates, discharges very quickly. The doubt I have is: Is this due to the chemistry of the cells installed in this module, or is it a connection problem with the cables that I am using (a supposition of which I have doubts because the conductors are 99% copper)
Hi Ayoub El Bendali, thank you for your answer. I´m careful and I have taken precautions to carry out this project.
Regadrs
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