Improved cycle performance of orthorhombic LiMn 0.95− xM xCr 0.05O 2; M = Al, Ga, Yb and In, synthesized by hydrothermal technique

Abstract

The effect of chemical substitution on improving cycle performance of orthorhombic LiMnO 2 ( o-LiMnO 2) was studied at the nominal compositions of LiMn 0.95− x M x Cr 0.05O 2; M=Al, Ga, Yb and In, 0.01< x<0.07. Samples obtaining single phase were synthesized by hydrothermal technique. As the result of studies, LiMn 0.92In 0.03Cr 0.05O 2 was confirmed as the optimum composition. The crystal structure refinement showed that chemical substitution varied the average ionic radii of cation sites in o-LiMnO 2. The ratio of average ionic radius at Mn site to that of Li site of the optimum compound was 0.87. This value was larger than that of no-substituted LiMnO 2; 0.84. TEM observation revealed that stacking faults were observed in the LiMn 0.92In 0.03Cr 0.05O 2 grains. It is assumed that these two factors, controlling ionic radii and introducing stacking faults, are key parameters for improving cycle performance. However X-ray diffraction data and discharge curves suggested that phase transformation from orthorhombic to cubic spinel occurred during charge–discharge cycle.