Structural and electrochemical effects of cobalt doping on lithium manganese oxide spinel

Abstract

Pure LiMn2O4 and lithium manganese oxide spinels with partial replacement of manganese by cobalt up to 20 mole%, LiCoxMn2−xO4, were prepared. The effect of extended cycling on the crystal structure was investigated. A capacity decrease with increasing cobalt content was observed in the potential range about 4100 mV vs. Li/Li+. Cycling behavior is significantly improved, compared to LiMn2O4. LiCoxMn2−xO4 is discharged in a single phase reaction in the upper potential range around 4100 mV vs. Li/Li+, whereas pure LiMn2O4 shows a two phase behavior. LiMn2O4 shows a significant broadening of peaks in plots of differential capacity and change in shape of the voltage profile upon extended cycling. LiCoxMn2−xO4 shows neither broadening nor change. Voltage profiles and plots of the differential capacity differ significantly compared to spinels with lithium substitution, Li1+xMn2−xO4. In contrast to Li1+xMn2-xO4, LiCoxMn2-xO4 is discharged in a two step process in the range of 0 ≤ × ≤ 0,5.