Investigating thermal runaway characteristics of ternary NCA lithium-ion batteries under varied aging conditions

Lithium-ion battery aging alters internal material properties and affects thermal runaway behavior. Therefore, understanding the heat generation and gas evolution characteristics of aged high-energy-density batteries is important for lifecycle safety management. In this work, a combined experimental and numerical approach was adopted to investigate thermal runaway initiation in batteries with different aging histories. A semi-empirical aging-coupled thermal runaway heat generation model was also developed and calibrated to explain differences in critical heat absorption and heat generation characteristics of NCA 21,700 batteries. The results indicate that: (1) Aging increases the internal short-circuit temperature, venting temperature, and thermal runaway trigger temperature of NCA batteries under thermal abuse, while decreasing the maximum surface temperature. This suggests improved separator stability. (2) Under normal-temperature aging, the critical heat absorption decreases, indicating a higher risk of thermal runaway, and the heat generation is mainly dominated by anode–electrolyte interfacial reactions. In contrast, under high-temperature aging, the critical heat absorption increases, and the heat generation is jointly governed by cathode decomposition and anode–electrolyte reactions. (3) CO is the dominant gas generated during thermal runaway. Its concentration is significantly higher in batteries aged at 40°C than in those aged at 25°C.