Failure mechanism of the lithium ion battery during nail penetration

Nail penetration is one of the most important methods to study the internal short circuit safety of lithium ion batteries (LIBs). A series of penetration tests on LIBs under different conditions are conducted. The effects of the states of charge (SOC), penetration positions, depths and speeds are analyzed. As for different penetration positions, thermal runaway reaction is more severe when the battery is penetrated at center due to the faster propagation of thermal runaway. The battery surface temperature is not positively correlated with penetration depth, and the temperature distribution becomes more nonuniform with the increasing of penetration speed. All batteries get into thermal runaway if their temperatures exceed 233 °C due to the shrinkage of separator and trigger of reaction between cathode and electrolyte. The fire behavior of penetrated batteries is exhibited in this work. “Micro short-circuit cell” structure is proposed to interpret the mechanism of internal short circuit induced by penetration.