Aging mechanisms and thermal stability of aged commercial 18650 lithium ion battery induced by slight overcharging cycling

Because of the inconsistency in battery pack and failure of charging device, slight overcharging of lithium ion batteries appears and even causes to thermal runaway. The aging behavior and mechanisms of lithium ion battery under slight overcharging cycling are studied qualitatively and quantitatively based on incremental capacity analysis and electrochemical impedance spectroscopy in this work. The results show that slight overcharging accelerates battery aging because of the loss of active material. While, conductive loss influences capacity fading less. The effect of lithium density loss is in the middle level. So it is suggested that incremental capacity analysis and impedance estimation are used to detect overcharging cycling on-line. Furthermore, the thermal stability of aged batteries are studied using Extended Volume Accelerating Rate Calorimeter. The results show that the stability of aged batteries become worse. The anode plays a key role in the thermal stability changes because of lithium plating under overcharging. The cathode dominates the stability after 70% SOH because of structure damage of cathode.