Effect of crack propagation of separator film of lithiumion battery cell on the development of internal short circuit

Internal short circuit is one of the main causes of thermal runaway. In this paper, the crack expansion rate of polypropylene separators for lithium-ion batteries is investigated under different stresses, temperatures, and initial crack lengths, and the formula for calculating the rate growth is fitted. Combined with the simulation results of stress and current factor in COMSOL, the separator crack expansion speed is related to the actual battery internal short circuit situation. We performed 100 cycles of 2C and 3C large magnification pulse charging experiments on the battery at a low temperature of −10 °C, as well as 100 cycles of 2C charging experiments on the battery at 25 °C after the low temperature. It was found that the self-discharge rate of the two batteries was eventually maintained between 3.12 % and 4.75 %. From this, we compare the internal short-circuit changes of lithium-ion batteries at different temperatures and multiplicities. Combined with our experimental analysis and the study of the literature, the effect of the crack expansion of the polypropylene separator of lithium-ion batteries on the internal short circuit of the batteries is discussed in depth.