Abstract: To prevent LiFePO₄ battery thermal runaway accidents, thermal runaway tests of 20 Ah LiFePO₄ battery were carried out in a combustion test chamber. Its combustion process, temperature characteristics, mass and voltage changes under three SOC were studied. The evolution of the jet flame was analyzed. The effects of SOC on surface temperature, flame temperature and mass loss were studied. And the phases of voltage change during thermal runaway were identified. The results show that during the combustion process, the thermal runaway process occurs twice, and the second thermal runaway process is more dangerous, that at most 5 jet flames are formed accompanied by flame liftoff, that as the SOC increases, the surface temperature, mass loss, fire risk and mass loss rate become larger, the combustion duration is inversely proportional to the SOC, that SOC has only a marginal effect on the temperature at different locations on the surface when thermal runaway occurs, and that the effect of SOC on both flame temperature and voltage is not significant.

Key words: lithium iron phosphate (LiFePO₄) battery, thermal runaway, state of charge(SOC), combustion process, temperature characteristics, mass loss, voltage change