Investigating the relationship between internal short circuit and thermal runaway of lithium-ion batteries under thermal abuse condition

Thermal runaway, a critical problem that hinders the application of lithium-ion battery, is always a thermal-electrical coupled process where exothermic chemical reactions and internal short circuit coincide and interact with each other. Clarifying the contributions of chemical reactions and internal short circuit to thermal runaway is crucial for developing safer lithium-ion battery. In this paper, the relationship between internal short circuit and thermal runaway of lithium-ion battery under thermal abuse condition is investigated through experimental and modeling approaches. Internal short circuit is observed to happen before thermal runaway but leads to little heat generation during thermal abuse test of a lithium-ion battery with Li(NiCoMn)1/3O2 cathode. Liquid-nitrogen-ceased thermal runaway test and postmortem analysis are designed to characterize the cause of internal short circuit. Thermal shrinkage of the separator is found responsible for the occurrence of internal short circuit. However, the joule heat from internal short circuit is limited by the sharp-increased battery resistance and thus contributes little to battery thermal runaway. Moreover, exothermic reactions between the anode and electrolyte are determined as the trigger of thermal runaway of the Li(NiCoMn)1/3O2–based battery, in contrast to the conventional views that the highly reactive oxygen released from cathode or internal short circuit is the critical factor for thermal runaway of lithium-ion battery. Finally, a model-based discussion on the effect of internal short circuit on the thermal runaway of batteries with different designs is presented. The results provide new insights into battery thermal runaway mechanism and can benefit the safety design of lithium-ion battery.