Understanding the influence of the confined cabinet on thermal runaway of large format batteries with different chemistries: A comparison and safety assessment study

Abstract

With the increasing development of large format lithium-ion batteries (LIBs) in automotive sectors, thermal runaway (TR) and fire hazards have become crucial challenges. A series of overheating experiments were performed on four large format LIBs with various chemistries under two conditions. To simulate the electric vehicle applications, the cabinet was employed in the confined space tests. The results showed that under the condition of stopping heating at safety venting (SV), all LiNixCoyMnzO2 (NCM) cells caught fire and TR, while no TR occurred for LiFePO4 (LFP) cells. The LFP cells cannot ignite spontaneously but only spray the electrolyte during TR. The triggering temperatures of TR for NCM cells are similar and close to the temperature of SV for LFP cells. For NCM LIBs, with the ratio of nickel increasing, the TR hazards increase, including the thermal and toxic hazards, larger than that of LFP cells. From the aspects of the TR risks and TR hazards, a safety assessment method was established to grade the fire hazards. Compared with open space tests, the LIBs with different chemistries in confined space tests have the same TR risks but lower TR hazards. The fire-induced toxicity was quantitatively evaluated by determining the fractional effective concentration and fractional effective dose. Moreover, the fire of LIBs is compared to the gas jet flame and pool fire of several typical fuels. Such a comparison analysis on large-scale LIBs with different chemistries can contribute to the selection of cells and safety design for automotive sectors.