Lithium transition-metal oxides Li(Mn2−x Co x )O4 (0≤x≤0.5) are synthesized by solid state reaction. X-ray and electrochemical data show that the replacement of Mn3+ (d4) ions by Co3+ (d6) in the octahedral framework of the spinel eliminates the local disorder present in the lattice around the [Mn3+O6] octahedra. The capacity loss observed in the undoped Li/LiMn2O4 cell is about 25% after 20 cycles, whereas that for the x=0.1 and 0.2 doped spinel materials is about 0.48 and 1%, respectively. The good capacity retention of Li(Mn2−x Co x )O4 (0.1≤x≤0.5) electrode is attributed to the stabilization of the spinel structure by Co doping for Mn ion sites. The chemical substitution of Co3+ for Mn3+ in LiMn2O4 improves the efficiency in maintaining electrochemical capacity over a large number of cycles without sacrificing initial reversible capacity at room temperature.