AN INVESTIGATION OF CAPACITY FADING OF MANGANESE SPINELS STORED AT ELEVATED-TEMPERATURE

The storage characteristics of a manganese spinel at various discharge depths and 80 degrees C were examined in 1 M LiPF6 ethylene carbonate /dimethyl carbonate (1:2 by volume) electrolyte. The quantities of Mn dissolution and discharge-capacity loss were measured after the cathod e at each discharge depth had been exposed to the electrolyte at 80 de grees C. The quantities of dissolved manganese in the solution were le ss than 1.2% of the total manganese in all cathodes examined. Little c apacity fading (3%) was found in the fully charged cathode, but a 59% capacity loss was observed in the fully discharged cathode. Correlatio ns of the capacity loss with the X-ray diffraction peak widths were fo und, and the amount of capacity loss increased with broadening peak wi dth. On the other hand, no correlation between the amount of Mn dissol ution and the capacity loss was found. From these results, we propose a mechanism of the capacity fading of the spinel LiMn2O4 stored at ele vated temperatures as follows: lattice defects in the spinel due to Mn dissolution cause disordered crystal structures and as a result, the Li insertion-extraction paths are blocked, leading to capacity fading.