Synergistic Na+ and F− co-doping modification strategy to improve the electrochemical performance of Li-rich Li1·20Mn0·54Ni0·13Co0·13O2 cathode

Abstract

The development of the high-profile Li-rich Mn-based cathode materials is limited by the high irreversible capacity loss, low rate performance, fast voltage decay and poor cycle durability. A synergistic modification strategy of Na+ and F− co-doping is implemented via carbonate co-precipitation followed by high-temperature solid-state reaction to enhance electrochemical properties of Li1·2Mn0·54Ni0·13Co0·13O2. The co-doping changes the lattice constant and expands the lithium layer spacing while maintaining well layered structure of the cathode materials, which accelerate the Li+ diffusion. F doping reduces the ratios of Mn4+/Mn3+ and Co3+/Co2+ from the transition metal valence state analysis and alleviates the erosion of the cathode materials with the electrolyte, preventing the dissolution of the transition metal ions. Besides, the structure evolution reveals that the Na+ and F− co-doping inhibits the transition metal ions transfer, thus blocking the spinel phase formation and stabilizing the layered structure of the cathode materials. As a consequence, co-doped cathode materials exhibit the synergistic advantages of both Na+ and F− ions, including increased initial reversible capacity (291.3 mAh g−1@0.1 C), considerably superior rate capability (144.3 mAh g−1@5 C), and remarkable cycle durability (84.8% retention even after 300 cycles). This study provides an alternative modification strategy for Li-rich Mn-based cathode materials with outstanding electrochemical performances.