Study on thermal runaway mechanism of 1000 mAh lithium ion pouch cell during nail penetration

The safety issues of lithium ion batteries (LIBs) have been serious as the popularity of LIBs in portable electronics and electric vehicles. It is necessary to understand the thermal runaway mechanism to effectively prevent thermal runaway. A series of nail penetration experiments are conducted to study the thermal runaway mechanism of lithium ion pouch cell in this work. It is observed that the pouch cell experiences four processes including nail penetration, internal short circuit, chemical reaction and thermal runaway during nail penetration. Additionally, four parameters, including state of charge (SOC), penetration speed, penetration position and nail diameter, are taken in the experiments to investigate the effect on thermal runaway. The results show that the cells with higher SOC and penetrated by bigger nail are easier to be triggered into thermal runaway and obtain higher temperature. The penetration position decides the location of the short circuit and the temperature distribution, and the steel nail has an influence on the temperature distribution of the cell. The results provide suggestions for the transportation, safe use and design of the cell.