Solid-state method and wet method were employed to synthesize spinel compounds LiNixMn2-xO4.The experimental results indicate that the capacity of high voltage at 4.7 V increase with the increase of amount of Ni. There are impurities in LiNixMn2-xO4 which were made by solid-state method. The sample LiNi0.5Mn1.5O4 had a capacity of 121 mAh/g at first cycle, in which 100 mAh/g was at high voltage range. Its cycle retention rate after 50 cycles was over 92%. The LiNi0.5Mn1.5O4 synthesized by wet method show a single spinel phase without impurity phase. It deliver a discharge capacity of 140 mAh/g in the first cycle, in which 125 mAh/g was at high voltage range. Its cycle retention rate after 50 cycles was over 96%. The XPS experiment results indicate that the oxidation states of Ni and Mn in LiNi0.5Mn1.5O4 made by wet method are +2 and +4 respectively.