Lithium-rich cathode material Li[Li0.2Ni0.13Co0.13Mn0.54]O2 was synthesized via a sol-gel method and Mg was successfully doped into this material. The charge and discharge tests reveal that doping with Mg substitution leads to improved electrochemical performance, which may provide an initial discharge capacity of 275.8 mAh g−1 at a current density of 40mAg−1 or a reversible capacity of 160.5 mAh g−1 at 1000mAg−1 within a potential range of 2.0-4.8V at room temperature. X-ray diffraction studies indicate the Mg substitution enlarges the inter-layer space which facilitates more effective lithium-ion insertion/extraction; cyclic voltammetry (CV) tests consistently show an increased ion diffusion coefficient (D Li). Such doping leads to significantly enhanced rate capability and cycling stability.