Abstract: The lithium-ion batteries for electric vehicle in the course of work will withstand the coupling of mechanical, electrical and thermal effects, in which mechanical abuse is one of the most important risks leading to the internal short circuit of lithium-ion batteries, which is likely to result in serious fire accidents. The mechanical integrity of separator is a key factor in preventing the internal short circuit of lithium-ion battery under the condition of mechanical abuse. Through comprehensive mechanical tests, it is found that different sizes of punches will lead to two distinct deformation and failure modes of PP separator. Finally, the mechanism of triggering internal micro-short circuit in lithium-ion battery is analyzed and a critical displacement criterion of separator under the internal micro-short circuit of lithium-ion battery is put forward based on mechanical tests and theoretical analysis

Key words: li-ion battery, mechanical abuse, separator, failure modes, internal micro-short circuit