Thermal runaway evolution of a 280 Ah lithium-ion battery with LiFePO4 as the cathode for different heat transfer modes constructed by mechanical abuse

Lithium iron phosphate batteries have been increasingly utilized in recent years because their higher safety performance can improve the increasing trend of recurring thermal runaway accidents. However, the safety performance and mechanism of high-capacity lithium iron phosphate batteries under internal short-circuit challenges remain to be explored. This work analyzes the thermal runaway evolution of high-capacity LiFePO4 batteries under different internal heat transfer modes, which are controlled by different penetration modes. Two penetration cases involving complete penetration and incomplete penetration were detected during the test, and two modes were performed incorporating nails that either remained or were removed after penetration to comprehensively reveal the thermal runaway mechanism. A theoretical model of microcircuits and internal heat conduction is also established. The results indicated three thermal runaway evolution processes for high-capacity batteries, which corresponded to the experimental results of thermal equilibrium, single thermal runaway, and two thermal runaway events. The difference in heat distribution in the three phenomena is determined based on the microstructure and material structure near the pinhole. By controlling the heat dissipation conditions, the time interval between two thermal runaway events can be delayed from 558 to 1417 s, accompanied by a decrease in the concentration of in-situ gas production during the second thermal runaway event.