Abstract: This paper studies the overcharge-induced thermal runaway characteristic of LiNi0.8Mn0.1O0.1O2-SiOx/graphite system 25 Ah pouch-shaped traction cells. Combined with the analysis results of the thermal characteristics of the electrode materials and gas production components during the thermal runaway process, the internal microscopic changes and dynamic heat generation characteristics of the cells during the thermal runaway triggered by overcharge in adiabatic and non-adiabatic environments was revealed. The path of overcharge triggering thermal runaway is: when overcharge causes the battery to exceed the safety margin voltage, side reaction and micro-short circuit of the pole piece occurred inside the cells, which generate gas and heat, and finally the cells overheat and reach the critical point of triggering thermal runaway. The trigger temperature of thermal runaway in adiabatic environment is 37.5 ℃ higher than that in non-adiabatic environment, and the triggering time in an adiabatic environment is shortened to varying degrees (about 90~500 s). In the end, the safety boundary and failure boundary of the cells were defined.

Key words: NCM ternary with high nickel ratio, overcharge, thermal runaway, lithium-ion battery