Abstract: Internal short circuit would be triggered when lithium ion batteries in nail penetration, it will generating massive heat and smokes and may cause thermal runaway damage. In this paper, the internal structure and thermogenesis mechanism of cylindrical LiFePO₄ battery after nail penetration are analyzed. An experimental platform for nail penetration test is established, Φ5 mm tungsten steel needle is used to penetrate the battery at initial ambient temperature 20℃. The battery thermal runaway process, battery voltage changes, battery surface temperature changes and so on are investigated. According to the experimental results, the following conclusions are obtained:(1) Intensity of thermal runaway about cylindrical LiFePO₄ batteries during nail penetration is random. (2) The battery voltage would drop to 0 V after battery penetrated, and will drop more rapidly if the battery sprays smoke and explodes. (3) The temperature of the battery will rise rapidly after nail penetration, and it will rise faster and higher as the battery belches smoke or explodes. The damage of nail penetration to the lithium iron battery is devastating and causes thermal runaway. Therefore, the battery structure should be designed to prevent nail penetration and provide extra protection.

Key words: LiFePO₄ battery, nail penetration, internal short circuit, thermal runaway