Li1+ x (Mn1/3Co1/3Ni1/3)1− x O2 (x ≥ 0) mixed oxides with different Li/M molar ratios (M = Mn1/3Co1/3Ni1/3) were obtained. The materials were characterized using chemical analysis, X-ray diffraction measurement, particle size distribution measurement, BET, and QOCV measurement. Rate performance and cycling performance were evaluated. Increased Li/M molar ratio, especially 1.10 < Li/M < 1.15, resulted in better cycling and rate performance as well as higher first cycle coulombic efficiency. As the discharge capacity is lower when Li/M molar ratio is greater than 1.10, the optimum ratio seems to be around 1.10.