Abstract: Overcharge is one of the primary factors that can trigger thermal runaway. However, there is a lack of discussion on the characteristics of thermal runaway behavior in energy storage battery cells with different capacities, and the variation rules of thermal runaway behaviors has not been clearly revealed. In this study, overcharge experiments were conducted on prismatic li-ion batteries of varying capacities. The results indicate that the battery compression force is the most sensitive parameter that changes early in thermal runaway, serving as an early warning signal. As the overcharging current rate increases, the distribution of heat and gas release during different stages of thermal runaway changes completely, leading to an increase in the total gas production. When the battery capacity is increased from 50 Ah to 280 Ah, both the gas production and heat generation increase rapidly with the gas release per unit capacity more than doubling, which significantly enhances the risk of thermal runaway.

Key words: Li-ion battery, overcharge, thermal runaway, capacity, heat release, gas release