Quantifying the Safety Evolution of Aging Large‐Capacity Lithium‐Ion Batteries

During long‐term operation, lithium‐ion batteries inevitably experience multidimensional aging, and these degradation processes markedly alter their safety responses under extreme conditions. To systematically elucidate the influence of aging on the thermal runaway characteristics of large‐capacity cells, this study quantitatively analyzes their safety behavior from three perspectives: temperature response, gas generation, and explosion limits. The results show that as aging severity increases, the onset temperature of thermal runaway decreases, the peak temperature rises, the total gas generation increases significantly, and the explosion limit range of the evolved gas mixture narrows, making the system more prone to entering flammable regions. Hazard analysis further indicates that the most pronounced safety degradation occurs in the Fresh–90% state of health (SOH) interval, with a much steeper decline compared with the subsequent 90%–80% SOH stage, suggesting that early‐stage aging contributes the highest increase in risk. Finally, this study establishes a multidimensional evaluation framework for assessing the thermal‐runaway‐related hazards of aged batteries, providing a scientific and effective basis for safety assessment and risk determination of end‐of‐life cells.