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.