Abstract: Nail penetration test is one of the most important methods to investigate the failure mechanisms and thermal runaway features of lithium-ion batteries. This paper summarizes the nail penetration testing methods commonly used by researchers and studies the influence of different variables, including penetration depth, velocity, location, needle material and diameter, on the short-circuiting and thermal runaway behaviour in batteries under nail penetration-induced damage. The results reveal a direct proportionality between the depth of nail penetration and the severity of thermal runaway behaviour in batteries. The speed of nail penetration has no significant impact on thermal runaway. When nail penetration occurs in regions with dense active materials or near the electrode, the thermal runaway in batteries becomes severer. As for the variables related to the nail itself, such as material and diameter, they exhibit a dual effect on thermal runaway behaviour in batteries, requiring separate analysis of heat generation and dissipation considering the actual conditions. Finally, by summarizing the influence of various factors on thermal runaway in batteries, new insights are proposed to mitigate lithium-ion battery thermal runaway and update safety testing procedures, which can provide guidance for subsequent innovative research work.

Key words: lithium-ion battery, nail penetration test, thermal runaway, internal short circuit, battery safety