Failure Mechanism\nStudy of Long-term Cycling Pouch\nCells with Lithium-rich Manganese-based Cathode Material

Lithium-rich\nmanganese-based (Li<sub>1.2</sub>Mn<sub>0.6</sub>Ni<sub>0.2</sub>O<sub>2</sub>, LRMOs) cathode materials with a special capacity\nof over 250 mAh/g have received widespread attention. However, the\ncurrent research mainly lies in cathode materials, and there is almost\nno research on their application in commercial pouch cell systems.\nIn this work, we use an LRMO cathode and graphite anode to assemble\na 2 Ah pouch cell cycled at 0.3 and 1 C at 25 °C and 1 C at 35\n°C, respectively. After 800 cycles, the harvest cathode and anode\nelectrodes were characterized in detail, and the lowest capacity retention\nwas observed at 0.3 C current density. The decline of battery capacity\nwas attributed to the longer duration of the samples at high voltage,\nresulting in the decomposition of the electrolyte, likewise the transformation\nfrom layered to spinel phases on the surface of the cathode material.\nXPS results also indicated that a large amount of electrolyte decomposition\nmaterial existed on the surface of the cathode electrode of the 0.3\nC samples. The loss of active Li in the cell system is the principal\nreason for the capacity drop of the LRMO pouch cell operating at a\nhigh voltage range. In addition, a proper temperature rise (25 to\n35 °C) does not bring more serious degradation and facilitates\nthe cell capacity release.