Surface F-doping for stable structure and high electrochemical performance of Li-rich Mn-based cathode materials

Li-rich cathode materials, i.e., Li1.2Ni0.13Co0.13Mn0.54O2 (LNCM), have gained increasing attention for their ultra-high specific capacity originating from the existence of anionic redox reaction. However, the anionic redox reaction on surface of LNCM can cause the oxygen release, thus leading to the collapse of the layered structure. F-doping is considered to be an effective strategy to inhibit the deterioration, but it meanwhile reduces the redox reaction participated by anions, resulting in the deterioration of the capacity. Herein, surface F-doped LNCM is carried out to suppress the oxygen release, while maintains the anionic redox reaction. As a result, the prepared surface F-doped LNCM cathode delivers a large specific capacity of 157.1 mAh·g−1 at 1 C, much higher than those of the bulk F-doped LNCM. More importantly, a large reversible capacity of 131.6 mAh·g−1 with a capacity retention of 78.3% can be obtained after 150 cycles at 1 C, while the bare LNCM cathode reserves a discharge capacity of only 5.9 mAh·g−1. By analyzing the morphology of the materials after cycling, it is confirmed that the improved electrochemical performance stems from the improvement of structural stability through F-doping.