Improved cycle performance of orthorhombic LiMn0.95−xMxCr0.05O2; M = Al, Ga, Yb and In, synthesized by hydrothermal technique

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 0.05 O 2 ; M=Al, Ga, Yb and In, 0.01 x 0.92 In 0.03 Cr 0.05 O 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 0.92 In 0.03 Cr 0.05 O 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.