Investigating thermal runaway triggering mechanism of the prismatic lithium iron phosphate battery under thermal abuse

Thermal runaway (TR), a critical safety issue that hinders the widespread application of lithium-ion batteries (LIBs), is easily triggered when LIB is exposed to thermal abuse conditions. Identifying the characteristics and trigger mechanism of TR induced by external heating is crucial for enhancing the safety of LIBs. Herein, based on overheating experiments, a detailed analysis is implemented from temperature, heat generation, and TR propagation velocity within the battery to reveal the TR triggering mechanisms at the cell level. Compared with the front heating mode, the bottom heating mode always results in severe TR accompanied by higher peak temperature, temperature increment, heat generation, and TR propagation velocity within the battery. The internal heat generation before TR makes a non-negligible contribution to the battery temperature increase and the trigger of TR, accounting for more than 35 %. The external heating quantity, heating power, temperature, and temperature gradient are the critical factors affecting the TR trigger when LIBs are exposed to thermal abuse conditions. TR is triggered by the decrease of the temperature gradient within the battery under the limited external heating quantity. Moreover, a theoretical model describing the battery TR trigger is proposed, revealing different TR triggering mechanisms under varied thermal abuse conditions.