NMC are no different in the internal resistance issue as LFP, they must be charged to a higher voltage and that settles over time to give a rested voltage.
The Cobalt content is the key difference between the two, Lithium Ferrous Phosphate does not generate oxygen when it gets heated beyond a certain point, the higher the Nickel content, the lower the temperature a fully charged cell starts to produce oxygen as the electrolyte and other materials begin to decompose as low as 70°C
If the temperature increases to 90°C, the cell becomes it's own heater, at 120°C the electrolyte starts to separate, it only requires another 10°C for the separator material between the two plates to start melting allowing any formed dendrite spikes to penetrate, creating a short between the two plates, serious heat generation now begins and there is no return from this point.
This is all occurs at the electrolyte level, the point where no more Li ions can be stored in the graphite, saturation charged, the excess of lithium ions in the electrolyte start to generate heat.
This is the reason for slowing the charge rate by lowering the current being pushed into the cell as it reaches 100% SOC, there are less spots available for the lithium ions to be stored in the graphite material, a higher than normal % of lithium ions in the electrolyte generates heat.
Can you see the correlation between pushing the cell voltage above the saturated graphite level, meaning that higher voltage is contained in the electrolyte, not stored in the differential between the plates .....
The electrolyte is already hot because it has been switching between over saturation and normal lithium ion concentration as it tries to ram ions into those last remaining spots available.
The electrolyte isn't all in contact with the cell casing, in fact, as the state of charge increases, so does material that makes up the cell plates, the conductor material and separator material also expands with heat, further reducing the electrolyte contact with the outside casing, so this heat is trapped deep inside the plate layers .....
Each time the electrolyte is pushed to the 70*C plus mark, the more dendrite is formed on the plate surfaces, resulting in a higher voltage potential to push the lithium ions through this layer of dendrite and then into the last few spots available to store them ...... this is the internal resistance that can be measured and causes the difference between charging voltage and discharging voltage.
Back to basic physics, we know what the byproduct of passing electricity through a resistor, heat .....
As I posted before, you might get away with it a few times, but the odds against it not going into thermal run away increase each time that electrolyte overheat occurs, hopefully, you can see the mechanics of why that occurs now
T1 Terry
and even Kirchoff knew that, back in 1845!
