Failure Mechanism Study of Long-term Cycling Pouch Cells with Lithium-rich Manganese-based Cathode Material

Lithium-rich manganese-based (Li1.2Mn0.6Ni0.2O2, LRMOs) cathode materials with a special capacity of over 250 mAh/g have received widespread attention. However, the current research mainly lies in cathode materials, and there is almost no research on their application in commercial pouch cell systems. In this work, we use an LRMO cathode and graphite anode to assemble a 2 Ah pouch cell cycled at 0.3 and 1 C at 25 °C and 1 C at 35 °C, respectively. After 800 cycles, the harvest cathode and anode electrodes were characterized in detail, and the lowest capacity retention was observed at 0.3 C current density. The decline of battery capacity was attributed to the longer duration of the samples at high voltage, resulting in the decomposition of the electrolyte, likewise the transformation from layered to spinel phases on the surface of the cathode material. XPS results also indicated that a large amount of electrolyte decomposition material existed on the surface of the cathode electrode of the 0.3 C samples. The loss of active Li in the cell system is the principal reason for the capacity drop of the LRMO pouch cell operating at a high voltage range. In addition, a proper temperature rise (25 to 35 °C) does not bring more serious degradation and facilitates the cell capacity release.