Multiple signal evolution process of thermal runaway in overcharged pouch cells with different capacities

Thermal runaway (TR) in lithium-ion batteries (LIBs) poses a significant risk that impedes their widespread application, particularly in large-scale settings. Battery capacity is a key factor influencing TR behavior, yet there is limited research analyzing the thermal runaway characteristics of pouch cells with varying capacities from multiple signals. In this study, a comprehensive series of experiments is conducted to investigate the evolution of multiple signals during overcharge scenarios for three pouch cells with capacities of 30, 40, and 50 Ah, aiming to clarify the impact of battery capacity on key parameters during overcharge. The results show that the battery swelling force signal notably increases when the surface temperature exceeds $40{ }^{\circ} \mathrm{C}$. Prior to the safety valve venting, the maximum growth rate of the swelling force is approximately ${60-90} \mathrm{N} / \mathrm{s}$. During the overcharging process, both the venting force and voltage of the battery increase wit the battery capacity, while the maximum temperature and peak temperature rise rate during thermal runaway remain relatively stable across all capacities, around $480{ }^{\circ} \mathrm{C}$ and $37^{\circ} \mathrm{C} /$ s, respectively. Generally, larger capacity batteries demonstrate a more pronounced temperature rise before the TR event, and at a given battery surface temperature, higher capacity batteries exhibit a greater temperature increase. These findings offer a more in-depth understanding of TR behavior in pouch cells and provide valuable insights for enhancing the safety design of larger-capacity batteries.