Measuring thermal response in 21700 lithium-ion cells from high current pulses using constant flux calorimetry

The introduction of nickel, manganese, cobalt-oxide (NMC) lithium-ion batteries in military systems allows for employment of new energy-and power demanding applications. However, such systems may imply high safety requirements as well as use during extreme conditions. This paper present a novel method using constant flux calorimetry to measure the thermal response of a single 21700-battery to estimate heat losses in the cell during discharging. Using a battery cycler, battery cells were discharged with repetitive high current pulses, with pulse width of 100 ms, a pulse repetition frequency at 1 Hz and current at 100 A for 2 minutes as well as with a constant current at 10 A for 2 minutes. These two discharge processes result in different amount of heat loss, were the losses during 100 A pulsing are around 15 times higher compared to that of the constant 10 A discharging. Despite this, Galvanostatic Electrochemical Impedance Spectroscopy (GEIS) measurements performed pre-and post-cycling, confirmed no significant performance degradation of the cell.