Comparative investigation of the thermal runaway and gas venting behaviors of large-format LiFePO4 batteries caused by overcharging and overheating

With the large-scale application of LiFePO4 (LFP) batteries in the field of electrochemical energy storage (EES), more attention is being paid to the problem of thermal runaway (TR). This paper investigates the TR and gas venting behaviors of 86 Ah LFP batteries caused by overcharging and overheating. Compared with previous studies, the main contributions lie in the gas venting behavior analysis of the LFP batteries during the whole TR process and the causes of the safety venting under overcharging and overheating. Two significant results are obtained from the experiments: (I) the overcharging of the LFP battery promotes gas release inside the battery, resulting in advance of safety venting, but the safety venting under overheating is caused by electrolyte volatilization; (II) the total gas volume (including H2, CH4, C2H4, CO and CO2) during TR under overcharging and overheating is 62.1 and 101.3 L. Moreover, the results calculated by the fractional compelling dose model show that there is no toxicity before TR under overheating. However, the duration of toxicity under the overcharge is 1211 s before TR. This work provides a meaningful theoretical guide for EES systems' safety warning and fire protection.