The gas production characteristics and catastrophic hazards evaluation of thermal runaway for LiNi0.5Co0.2Mn0.3O2 lithium-ion batteries under different SOCs

Lithium-ion batteries (LIBs) are widely used as electrochemical energy storage systems in electric vehicles due to their high energy density and long cycle life. However, fire accidents present a trend of frequent occurrence caused by thermal runaway (TR) of LIBs, so it is especially important to evaluate the catastrophic hazards of these LIBs. This study conducted the adiabatic TR test coupled gas production test, Gas Chromatography-Mass Spectrometry test, and explosion limit test on a commercial LIB with Ni0.5Co0.2Mn0.3 as the cathode material at different states of charge (SOCs). The results show that the TR temperature and the maximum temperature at low SOC are lower compared to that at a high SOC. The probability of LIBs TR at less than SOC = 50 % is small and also causing less harm. For the gas production characteristics, the lower the SOC of the battery, the lower the gas production volume. The peak and steady-state gas production increase with the increase of SOC. For the mixed gases generated during TR, the content of CO2 shows a trend of decreasing with the increasing of battery SOC, while that of H2 and CO increase with the increasing of SOC. For the explosion limit of the mixed gas, the lower explosion limit and upper explosion limit decrease and increase with the increasing of SOC, respectively. Finally, based on the seven parameters related to the TR gas production of LIBs and so on, the analytic hierarchy process method was used to establish a LIB TR disaster-causing hazard evaluation system. The evaluation system can quantitatively evaluate the thermal safety of a LIB. This is instructive for establishing a comprehensive quantitative evaluation method for battery safety in practical engineering applications.