Lithium-rich layered oxide materials of Li1.2Mn0.54Ni0.13Co0.13O2 have been successfully synthesized through a facile one-step coprecipitation method without the use of any toxic chelating agent. The structure and morphology of the as-prepared Li1.2Mn0.54Ni0.13Co0.13O2 cathode material were well optimized by tuning synthesis parameters including the co-precipitation pH value, the feeding rate of metal precursors and the reaction temperature. The optimal Li1.2Mn0.54Ni0.13Co0.13O2 spherical particles present well-ordered layer structure and low cation-mixing degree. As a result, Li1.2Mn0.54Ni0.13Co0.13O2 as a cathode material presents excellent reversible capacity, rate capability, and cycling performance, which delivers a high initial discharge capacity of 255 mAh g−1 and 172 mAh g−1 at 0.1 C and 1 C, respectively. Moreover, a discharge capacity of 155 mAh g−1 can be maintained even after 300 cycles at 1 C, corresponding to a capacity retention as high as 81%.