Revealing the Impact of High Current Overcharge/Overdischarge on the Thermal Safety of Degraded Li-Ion Batteries

To analyze the impact of two commonly neglected electrical abuse operations (overcharge and overdischarge) on battery degradation and safety, this study thoroughly investigates the high current overcharge/overdischarge effect and degradation on 18650-type Li-ion batteries (LIBs) thermal safety. Based on the temperature-voltage behavior and induced thermal runaway (TR) mechanisms, the overcharge and overdischarge-triggered TR processes are divided into four and three stages. Furthermore, the degradation effect is analyzed by analyzing the incremental capacity-differential voltage curves. During the high current cycling process, lithium inventory decreases significantly. Besides, the active material decreases when the battery degrades to a certain level. Lithium plating is the primary reason for lithium inventory loss; the plated lithium grows with the increment of degraded/overcharged level. Besides, the dissolution and deposition affect the internal short circuit degree, which can be observed from the electrode potential and cell voltage value. Moreover, battery cells undergo different degradation degrees, and different current rates of charging/discharging exhibit similar temperature-rising trends during the adiabatic TR tests. However, with the degradation degree increase, battery capacity fades, TR becomes easier to be triggered by the high current rate, and TR reactions are severe. This study guides early quantitative detection, safer battery cell design, and enhanced thermal safety management.