Metal oxide-coated spinel was investigated with respect to electrochemical characteristics. Metal oxide coating on commercial spinel powder (LiMn2−x M x O4, M=Zr, Nikki, Japan) was carried out using the sol–gel method. Al2O3/CuO x -coated spinel exhibited stable cycle performance in the range from 3.0 to 4.4V, and it had lower charge transfer resistance and higher double layer capacitance than bare spinel in later cycles. In the SEM image of the powder after the cell test, bare spinel showed abnormal surfaces formed by decomposition of the electrolyte, while Al2O3/CuO x -coated spinel displayed a normal surface covered with a surface film. Therefore, it is expected that an Al2O3/CuO x layer coated on the spinel powder can function as a protective film, which supresses the reaction between electrolyte and active material.