Synergistic coupling effect of sodium and fluorine co-substitution on enhancing rate capability and cycling performance of Ni-rich cathode for lithium ion battery

The poor rate performance and inferior cycling life of Ni-rich layered oxide cathodes, which are related to low lithium conductivity and structure degradation during cycling, are the obstacles to commercial utilization. Herein, we apply a solid grinding approach based high temperature calcination to synthesize Na-substituted, F-substituted and Na-F-substituted LiNi0.6Co0.2Mn0.2O2. The synergistic coupling effect of both sodium and fluorine substitution on particle morphology and structure is systematically investigated. The galvanostatic charge/discharge results show that Na and F co-substituted sample displays improved rate performance as well as superior capacity retention. The cooperative substitution of Na and F has synergistic effect on enlarging the interlayer spacing, which is favorable for increasing lithium diffusivity and enhancing the rate capability. Meanwhile, the Na incorporated into the Li layer and the partial substitution of metal-O bond by stronger metal-F bond can help to stabilize the crystal system, thus enhancing the structural stability. This work presents some new thought into synthesis of high-performance cathode materials through strategic cationic-anionic co-substitution.