Li- and Mn-rich layered oxides as cathode materials attract considerable attention owing to the superior capacity. However, their practical applications are still hindered by the inherent drawbacks such as the poor rate capability. Based on the structure characteristics that Li diffuses through two-dimensional lithium ion diffusion tunnel during intercalation/extraction, enlarging Li layer spacing is an effective strategy to increase Li+ diffusion coefficient and enhance rate capability. In this work, Mg-doping in Li site is employed to enhance the electrochemical performance of Li1.133Ni0.2Co0.2Mn0.467O2. With the ionic radius similar to that of Li+, Mg2+ is more suitable to occupy Li site and enlarge lattice parameter c which is critical to Li layer spacing and lithium ion diffusion coefficient. Consequently, Li1.123Mg0.010Ni0.2Co0.2Mn0.467O2 exhibits high initial capacity of 308 mAh g(-1) at 25 mA g(-1) and better rate capability as high as 166.1 mAh g(-1) at 625 mA g(-1) under 2.0-4.8 V vs. Li/Li+. Its ionic conductivity at 4.1 V during charge and 3.7 V during discharge is 4.1 * 10(-12) cm(2).s(-1) and 9.2 * 10(-13) cm(2).s(-1), 6.10 times and 6.07 times higher than that of pristine sample, indicating that magnesium doping facilitates the migration and diffusion of Li+ due to the enlargement of lithium ion diffusion channel.