Investigation of gas explosion hazards and characteristics during overcharged behavior of nickel-cobalt-manganese (523) lithium-ion battery

Compared with hard-shell lithium batteries, the obvious thermal runaway (TR) characteristic of nickel‑cobalt‑manganese pouch cell (NPC) is that it cannot release a large amount of gas in time. Therefore, the fire risk during the TR process of NPC is centralized by gas explosion hazard. The overcharged TR process of nickel‑cobalt‑manganese (523) NPC (NCM523) was explored in this work. The jetting flame phenomenon still occurs during the TR process of NCM523 in the absence of air, indicating that it is primarily attributed to self-reaction and exhibits spontaneous properties. Moreover, the air environment can increase the intensity of jetting and gas explosion hazards. The gases produced during the TR process of NCM523 in the air and nitrogen are mainly CO, H₂, N₂, CO₂, CH₄, C₂H₆, C₂H₄, and C₃H₆. The volume percentages of combustible gases in the air and nitrogen are 64.87 % and 46.24 %, respectively. The lower explosion limit (volume ratio) of gases in the air environment is between 10 % and 11.25 %, while the upper is between 39.37 % and 40 %. The maximum flammable intensity of gases generated from the TR process of NCM523 is 25 %. As revealed by CHEMKIN simulations, H∙, O∙, and OH∙ are the most important key radicals that catalyze the entire chain reaction and gas explosion during the TR process of NCM523. The interaction and mutual promotion of reactions R1, R2, and R3 are crucial for the generation of free radicals. Therefore, the combustion and explosion risk during the TR process of NCM523 can be reduced by increasing inert gases and suppressing the free radical reaction chemically during gas phase combustion.