Thermal Runaway Behaviors and Kinetics of NCM Lithium-Ion Batteries at Different Heat Dissipation Conditions

The lithium-ion battery (LIB) thermal runaway is triggered by the exothermic reactions between electrode materials and other active substances such as electrolytes. In this study, the effects of ambient temperature and heat transfer coefficient on the thermal responses and chemical kinetic features of LiNi 1/3 Co 1/3 /Mn 1/3 O 2 /graphite battery thermal runaway at high-temperature abuse conditions are investigated using a validated 2D axisymmetric model. With varied heat transfer coefficients of the LIB, the corresponding runaway, critical, and safety operation zones at different ambient temperatures are quantitatively distinguished. The results reveal that, with increased heat transfer coefficient, the critical ambient temperature, T c , triggering thermal runaway increases. However, T c almost remains 430 K when the heat transfer coefficient is higher than 25 W/(m 2 K). Additionally, based on the thermal response of LIB, the ambient heat absorption stage, ambient heat dissipation stage, and dramatic heat release stage in thermal runaway are defined. It is found that a higher heat transfer coefficient efficiently causes a shorter ambient heat absorption stage, which is the primary reason for the reduced delay time for the thermal runaway. Further, kinetic analysis is conducted at different heat exchange conditions, and the correlation between LIB thermal responses and the heat release of side reactions in different operation zones is clarified. Specifically, the reactions between the electrolyte and negative/positive electrodes are the most exothermic and most influential of all side reactions, and their influence on the maximum temperatures and runaway delay times is promoted with an elevated heat transfer coefficient.