NH4F surface modification of Li-rich layered cathode materials

•The Li1.2Mn0.54Ni0.13Co0.13O2 is synthesized and modified by NH4F.•The NH4F surface modification causes phase transition.•Rate capability and cycling stability of the material are significantly improved.•The mechanism of enhancement in the electrochemical properties is investigated.

In this work, a Li-rich layered Li1.2Mn0.54Ni0.13Co0.13O2 cathode material synthesized by a coprecipitation method is further treated by NH4F. Material characterizations and electrochemical measurements show that the surface modification leads to a phase transition from the original layered phase to a spinel-like phase at the particle surface. It is found that the rate capability and cyclability of Li1.2Mn0.54Ni0.13Co0.13O2 can be significantly improved, which could be attributed to the locally transformed spinel-like structure and F- ion doping at the particle surface, which favor fast lithium ion diffusion and structural stability.