Mixed-polyanion LiV(SixP1−xO4)F/C (0 < x < 1) cathode materials for lithium ion batteries

High-performance lithium ion batteries (LIBs) are increasingly important to help achieve the global aim of carbon neutrality. As a promising cathode material for LIBs, LiVPO4F presents better thermal stability and higher theoretical specific energy than current LiFePO4. However, its practical performance is severely constrained by the low electric conductivity and sluggish electrochemical kinetics. Herein, a new type of mixed-polyanion LiV(SixP1−xO4)F/C (0 < x < 1) is designed and explored by lightly substituting phosphorous with silicon. The phase structure, particle size and morphology are not obviously affected, while some V3+ is oxidized to V4+ because of the charge compensation of SiO44- with PO43-. The optimized LiV(Si0.05P0.95O4)F/C shows noticeably enhanced electrochemical performance compared with pristine LiVPO4F/C and similar LiVPO4F/C materials reported in recent literature. The specific discharge capacities of 143 and 127 mA h g−1 are achieved at 0.1 and 8 C, respectively. In addition, LiV(Si0.05P0.95O4)F/C shows a capacity of 111 mA h g−1 after 1000 cycles at 1 C, corresponding to a capacity decay of only 0.019 % per cycle. The remarkable performance is ascribed to the reduced electrochemical resistance and significantly improved Li+ diffusivity. This work demonstrates the significance and feasibility of polyanion regulation for high-performance polyanionic battery materials.