Mechanical Abuse Behavior and Twice Thermal Runaway Evolutions of a 280 Ah Lithium Ion Battery with Lifepo4 as Cathode Under Different Penetration Modes

Because of the recurring electric vehicle safety accidents, lithium iron phosphate battery has been utilized more and more in recent years with higher safety performance. In this study, the heat transfer path of battery thermal runaway is controlled by changing the diameter of the nail and the penetration depth. Two penetration cases involving completed penetration and incompleted penetration are detected during the test, as well as two modes incorporating of remaining and removing nails after penetration are performed to reveal the thermal runaway mechanism comprehensively. Compared with the previous studies, this paper analyzes the thermal runaway behavior of large-capacity lithium iron phosphate battery under different heat generation and heat dissipation modes and finds the phenomenon of twice thermal runaway of double cores battery. The danger of the above penetration mode and the twice thermal runaway is analyzed quantitatively. Additionally, a theoretical model of the microcircuit and internal heat conduction is established. The results show that the twice thermal runaway is caused by penetration and heat abuse respectively, and the maximum time difference between them can reach 1417 s in the experiments, which results in uneven distribution of electrolyte inside the battery and a large difference in battery gas production. Furthermore, the trigger of thermal runaway is affected by the diameter and insertion depth of the steel needle, while the whole process is affected by heat dissipation, and the voltage will not drop before the second thermal runaway. These results provide some guidance for early warning and firefighting of batteries.