Influence of Overdischarge Depth on the Aging and Thermal Safety of LiNi_0.5Co_0.2Mn_0.3O₂/Graphite Cells

ABSTRACT Overdischarge is one of the potential factors that affect the performance and safety of lithium‐ion batteries (LIBs) during application. In this study, the aging behavior and thermal safety of LIBs at different overdischarge cut‐off voltages are investigated. The results show that overdischarge significantly affects the discharge ability of the battery, with a capacity decay rate of 38.2% at an overdischarge cut‐off voltage is 0.5 V. Electrochemical test results indicate that overdischarge accelerates the loss of the active materials and the increase of impedance. Quantitative analysis shows that the conductive loss and lithium inventory loss are the main causes of battery aging. The disassembly images and further physicochemical characterization indicate that with the decrease of overdischarge voltage, the dissolution of copper current collector and the increase of electrode surface attachments intensify. The differential scanning calorimetry test indicates that the thermal stability of the anode is reduced. These aging behaviors lead to the loss of active materials, the damage of the electrode structure, and the increase of gas production inside the overdischarge batteries, which results in the advance of the thermal runaway time, the decrease of the thermal runaway onset temperature and the thermal runaway peak temperature.