Slight Overcharge Aging Behaviors and Thermal Runaway Characteristics of Li(Ni_0.5Co_0.2Mn_0.3)O₂/Graphite Batteries at Different Ambient Temperatures

Lithium-ion batteries overcharging at different ambient temperatures exhibit different aging behaviors, which can affect the electrochemical performance and thermal safety. In this paper, the aging mechanisms and thermal stability of Li(Ni_0.5Mn_0.3Co_0.3)O₂/graphite batteries after overcharging at different ambient temperatures are studied comprehensively. First, the effect of different ambient temperatures on the aging modes is analyzed at different overcharge voltages by incremental capacity-differential voltage technology. Then, the morphology and composition changes of electrodes are studied by postmortem characterization analysis. Finally, the evolution of thermal runaway is revealed by accelerating rate calorimetry tests. The results indicate that the main aging modes are LAM and LLI during overcharge cycling at 0 °C. Overcharge cycling at 25 and 45 °C, the primary aging mode is LAM. As ambient temperature increases, the degree of ion mixing increases. Lithium plating occurs on the anode surface after overcharge cycling at 0 °C. After overcharge at 25 and 45 °C, the SEI film on the anode surface thickens and the cathode structure is damaged. Compared with the fresh battery, thermal runaway characteristic temperatures of overcharged batteries decrease obviously. In particular, the exothermic initiation temperature of batteries overcharged at 0 °C is reduced, which means that the thermal stability of batteries is reduced compared with that of the batteries overcharged at 25 and 45 °C.