Li-rich Mn-based Co-doped Li[Li x Mn0.65*0.995(1−x)Ni0.35*0.995(1−x)Co0.005(1−x)]O2 and none-doped Li[Li x Mn0.65(1−x)Ni0.35(1−x)]O2 cathode materials were prepared by a conventional solid-state reaction. The initial charge and discharge test were carried out in the voltage ranges of 2.0–4.8V and 2.0–4.6V, then change to 3.0–4.3V for cyclic test. XRD revealed that all the materials prepared show a (003) peak at 2θ =18.5° as a main peak and clearly present a pure hexagonal structure. SEM characterization proved that the as prepared materials are constituted of small and homogenous particles. The Co-doped Li[Li0.0909Mn0.588Ni0.3166Co0.0045]O2 sample expresses highest initial efficiency of 78.8% and highest energy density of 858.4mWhg−1, while the none-doped Li[Li0.2308Mn0.5Ni0.2692]O2 sample behaves lowest of 56.5% and 590.1mWhg−1. Furthermore, discharge capacity keeps on going up at the initial stage of cyclic process, which can reach the highest discharge capacity approximately in the fifth cycle. Almost no capacity loss is observed after 30 cycles.