Analysis of Gas Release During the Process of Thermal Runaway of Lithium-Ion Batteries with Three Different Cathode Materials

The process of thermal runaway (TR) of lithium-ion batteries (LIBs) is often accompanied by a large amount of heat generation and gas release. However, the gas release behavior during the process of TR remains unclear. Three types of 26700 LIBs with LiFePO4 (LFP), LiMn2O4 (LMO) and LiNi0.5Co0.2Mn0.3O2 (NCM) as cathodes are triggered to TR, respectively. Subsequently, the gas releases behavior of fully charged batteries during the TR process is obtained. Before the battery temperature approaches the uncontrollable temperature, the electrolyte volatilization and gas releasing are decoupled, the gas release of LFP, LMO and NCM batteries are 0.094 mol, 0.042 mol and 0.058 mol, respectively. These gases account for 29.1, 75.2 and 55.4% of the gas volume that cause the safety valve to open in the LFP, LMO, NCM batteries, respectively. After battery temperature approaches the uncontrollable temperature, the reasons for the rapid increase in total pressure are qualitatively analyzed by investigating the structural changes of the cathode materials before and after TR. For the LFP battery, the gas release is found to be the main cause of the structural change, and for the LMO and NCM batteries, the impact force is the dominant cause.