Influence of Charge Cutoff Voltage on the Cycling Behavior of LiNi_0.5Mn_0.3Co_0.2O₂Cathode

Layered oxide, LiNi0.5Mn0.3Co0.2O2 (NMC532), is commonly used in the commercial high energy Li-ion batteries. However, such layered oxide cathode always faces the dilemma between high capacity and stable cycling. Upper charge cutoff voltage is one of the important factors that strongly influences both capacity and cycle life, unfortunately, exhibiting an opposite effect. A choice of an appropriate upper charge cutoff voltage is expected to achieve the balance between these two performance metrics. Therefore, it is of great significance to comprehensively understand the effect of incremental upper voltages, ranging from normally used cutoff voltage to slight overcharge voltage, on the cycling behaviors of the NMC532 cathode material. In this work, the systematic studies about the effect of the upper voltage on the NMC532 cathode material are investigated. Physical characterizations, i.e., ex situ synchrotron X-ray diffraction and X-ray absorption spectroscopy, provide information on the degradation of NMC532 material. Post-mortem analysis via combined scanning electron microscopy and electrochemical impedance spectroscopy reveals the degradation of the cathode-electrolyte-interface at high voltages. This comprehensive study shows the fundamental interplay among many electrochemically relevant factors, especially at different charge cutoff voltages.