Capacity fading of LiCr0.1Mn1.9O4/MPCF cells at elevated temperature

Abstract

Capacity fading of LiCr0.1Mn1.9O4 /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 LiCr0.1Mn1.9O4 exhibited good effects on restraint of Mn dissolution and stabilization of structure at 55 °C. The cycled LiCr0.1Mn1.9O4 electrode and the cycled MPCF electrode presented good electrochemical performance again with fresh electrolyte. Therefore, it was proposed that the cycling fading of LiCr0.1Mn1.9O4/MPCF cells was mainly caused by decomposition of electrolyte upon LiCr0.1Mn1.9O4 electrode during cycling. It was found that the decomposition of electrolyte led to the formation of a surface layer comprised of Li2CO3, LixPFy, CH3OCO2Li or (CH2OCO2Li)2, polymeric ether etc. The formation of this film consumed active lithium ions, leading to fast capacity fading of LiCr0.1Mn1.9O4/MPCF cell at elevated temperature.