Internal temperature and flame jet characteristics during thermal runaway triggered by nail penetration for NCM811 lithium-ion battery

The thermal runaway (TR) of NCM811 Lithium-ion battery (LIB) triggered by nail penetration was tested under three cases of full depth@100%SOC, half depth@100%SOC, and full depth@50%SOC, respectively. The internal temperature of the battery was measured by the built-in thermocouple, the fire behavior in four stages during TR was recorded by high-speed photography, the flame intensity was quantified by image processing method, and the internal structure of the battery was studied after TR. The results show that the effect of SOC on thermal runaway is more significant than that of penetration depth. In the case of full depth@100%SOC and full depth@50%SOC, the internal peak temperature is 887.3 °C and 483.2 °C, the maximum temperature difference between the internal and surface is 256.3 °C and 92.9 °C, the maximum jet angle is 72.0° and 47.9°, the jet area duty ratio is 41.2% and 17.8%, and the mass loss is 41.7 g and 18.6 g. For different cathode materials, the thermal runaway of NCM811 LIB is more serious than that of NCM532 LIB. For different trigger modes, the thermal runaway of NCM811 LIB triggered by nail penetration is more serious than that triggered by external overheating.