Effects of charging rates on heat and gas generation in lithium-ion battery thermal runaway triggered by high temperature coupled with overcharge

Lithium-ion batteries are susceptible to thermal runaway incidents at high-temperature abuse and overcharging conditions. This study employs an experimental approach that combines an accelerating rate calorimetry with a battery testing system to investigate thermal runaway behaviors in 18,650-type LiNi1/3Co1/3Mn1/3O2 cells at high temperatures, particularly during constant current constant voltage (CCCV) charging at rates of 0.2C, 0.5C, 1C, and 2C. The results reveal that cells coupled with charging behavior exhibit a greater potential for thermal runaway at high temperatures, and increased charging rates lead to increased irreversible heat and promoted side reactions, which ensure advanced thermal runaway events and enhanced heat and gas generation capacity in the cell. Furthermore, owing to the combined influences of stage of charge and the promoting effect of charging current on side reactions, the total heat and gas production and the charging rate exhibit a nonlinear relationship. Eventually, after the completion of charging, the relationship between gas generation rate and heat generation rate can be characterized by two linear growth stages. The initial stage displays consistent gas generation rates despite variations in charging rates, and the subsequent stage demonstrates different gas generation rates with increased charging rates, suggesting alterations in side reaction pathways.