Capacity fading of LiCr_0.1Mn_1.9O₄/MPCF cells at elevated temperature

Capacity fading of LiCr_0.1Mn_1.9O₄ /MPCF (mesophase pitch-based carbon fiber) cells was investigated at elevated temperature (55 °C). The cells showed very fast capacity fading, keeping only 60% of capacity retention at the 100th cycle at 55 °C. The cycled electrodes and the electrolyte were analyzed using electrochemical test, inductively coupled plasma, and X-ray diffraction. Results of the analyses indicated that LiCr_0.1Mn_1.9O₄ exhibited good effects on restraint of Mn dissolution and stabilization of structure at 55 °C. The cycled LiCr_0.1Mn_1.9O₄ electrode and the cycled MPCF electrode presented good electrochemical performance again with fresh electrolyte. Therefore, it was proposed that the cycling fading of LiCr_0.1Mn_1.9O₄/MPCF cells was mainly caused by decomposition of electrolyte upon LiCr_0.1Mn_1.9O ₄ electrode during cycling. It was found that the decomposition of electrolyte led to the formation of a surface layer comprised of Li ₂CO₃, Li _x PF _y , CH ₃OCO₂Li or (CH₂OCO₂Li)₂, polymeric ether etc. The formation of this film consumed active lithium ions, leading to fast capacity fading of LiCr_0.1Mn_1.9O ₄/MPCF cell at elevated temperature.