Comparative study on aging and thermal runaway of commercial LiFePO₄/graphite battery undergoing slight overcharge cycling

Overcharging may occur due to the inconsistency of lithium-ion batteries (LIBs), which is likely to trigger battery failure or thermal runaway (TR). Herein, the aging mechanism and TR behavior of aged LiFePO₄ batteries induced by different degrees of slight overcharge cycling are studied. First, the capacity degradation and aging mechanisms are studied qualitatively and quantitatively by conducting in-situ experiments. The results indicate that the high cut-off voltage (4.5 V) accelerates capacity fading, which is dominated by loss of lithium. However, capacity retention is benefited if the overcharge voltage is properly increased (4 and 4.2 V). Then, the TR behavior of cells is tested using the extended volume accelerating rate calorimeter (EV-ARC). The results indicate that the thermal stability of aged cells worsens because the internal short circuit is more likely to occur due to lithium plating on the anode experiencing overcharge cycling. Finally, the intrinsic interaction between the aging mechanism and TR features of slightly overcharged LIBs is revealed. Meanwhile, we also provide valuable information regarding the reusability of LIBs undergoing overcharge cycling. Therefore, this study is useful for battery safety design and early warning of TR.