In this work, a facile method has been developed to synthesize Li1.3Al0.3Ti1.7(PO4)3 (LATP) coated Li1.2Ni0.2Mn0.6O2 and its electrochemical properties have been optimized through tuning the LATP content and heating temperature. Electrochemical tests indicate that 3wt% LATP-coated sample (heated at 575 °C) shows the best performance with a discharge specific capacity of 264.7 mAh∙g−1 at 0.1 C in first cycle and the capacity retention of 94.3% after 80 cycles at 0.2 C. Furthermore, the voltage decay of Li1.2Ni0.2Mn0.6O2 is restrained significantly after 3wt% LATP coating. The high structure stability of LATP is beneficial to restrain the side reactions and results in enhanced cycle performances Li1.2Ni0.2Mn0.6O2. The electrochemical impedance spectroscopy (EIS) analysis shows that the charge transfer impedance for Li1.2Ni0.2Mn0.6O2 is reduced and the lithium ion diffusion coefficient has increased significantly by more than four times after LATP-coating. The low charge transfer impedance and high ion diffusion coefficient are responsible for the better rate capability of LATP-coated Li1.2Ni0.2Mn0.6O2.