Investigation of the Thermal Hazard of Faulty Li-ion Battery under External Heating

Lithium-ion battery tends to explode whenever abused beyond its critical tolerance. However, it is rare for the faulty battery (non-working) to be examined against abuses to investigate its related thermal consequences. In this study, a series of experiments is established to investigate the thermal hazards of faulty Li-ion battery during external heating by studying their combustion behavior and associated thermal consequences; and later results are compared with those of working batteries. The working batteries were charged to 75% and 100% SOC before testing. A group of a faulty battery and working battery were externally heated by an electric heater and the battery surface temperature and flame temperature were recorded throughout a test series. The thermal behavior of the battery was characterized by the battery surface temperature capture by a thermocouple attached on it whereas the flame temperature was captured by five thermocouples located on top of the positive cap. Results showed that, incidents such as gassing, safety vent crack, onset to thermal runaway, ignition, explosion, and extinguishing were similar in both faulty and working battery, but they were increasingly energetic failures. It is found that a faulty battery triggered to thermal runaway at about 314 °C and reached a maximum surface and flame temperatures of 422 °C and 512.6 °C, respectively. The 100% SOC battery exhibited lower temperature to gassing, safety vent crack and ignition compared to others, whereas 75% SOC battery depicted the highest flame temperature due to energetic and stable combustion. Of great interest is that, all samples, faulty and working batteries, attained their maximum flame temperatures between explosion and extinguishing incidents. Moreover, the hottest region in all samples was within 40 mm from the positive cap. Post-test observations showed that after energetic explosion, the internal pressure in the battery reduces drastically so that ejecta are not expelled farther. At the same time, another flame emerges which burns for some time in the region of 40 mm from the positive cap. Another reason that contributed to the localization of the flame at the region of 40 mm from the positive cap is the safety vent clogging and melting of the Aluminum sheet which blocked or hindered the clear passage of the combustible gases. Thus, it can be concluded that, to enhance the safety, care should still be taken while handling the faulty battery.