Mechanical properties and thermal runaway study of automotive lithium-ion power batteries

Abstract

As the most widely used power battery for pure electric vehicles, lithium-ion battery has been studied in detail, including electrochemical performance and mechanical safety. This paper focuses on the mechanical response and thermal runaway phenomena caused by external mechanical stress of lithium-ion batteries at different states of charge (SOC). The results show that the SOC affects the mechanical strength as well as the temperature of the battery under external stress. When stress is applied to the cell, the higher the SOC of the cell, the higher its stiffness and surface temperature. The force is determined to propagate layer by layer based on the dynamic analysis approach of stress propagation theory. The velocity is inversely proportional to the stress propagation distance. Excessive impact velocity will lead to concentration of stress in the battery, which will lead to short circuit and thermal runaway phenomenon of the battery. The findings of these phenomena are of guiding significance to the safety study of electric vehicle lithium-ion batteries.

Safety Performance and Failure Criteria of Lithium-Ion Batteries under Mechanical Abuse

“…Refs. [35][36][37] also indicate that batteries with higher SOC exhibit increased stiffness. The research by Chen et al demonstrates that after charging, the battery core expands, resulting in a change in stress that causes the steel shell to be stretched, leading to the phenomenon of increased battery stiffness [38].…”

“…Wang et al's experimental results indicate that batteries with high SOC are more susceptible to thermal runaway under equivalent deformation conditions [15,22,34] (Figure 10). Batteries with high SOC exhibit a faster rate of temperature increase when subjected to mechanical abuse, and this is due to the fact that batteries with high SOC also generate higher currents after experiencing mechanical abuse, resulting in the release of larger amounts of heat [37]. Ren et al also pointed out in the literature [40] that for batteries with a low state of charge (SOC), the heat generated during the internal short circuit (ISC) is smaller and the chemical reactions inside the battery are still controllable.…”