Off-stoichiometric NaxV2(PO4)3 as cathode material for sodium-ion batteries

The NASICON-type compound Na3V2(PO4)3 (NVP) has garnered significant attention as a promising cathode material for sodium-ion batteries. However, the practical application of the NVP cathode still face challenges due to its intrinsic limitation of electronic conductivity and cycling stability. Herein, a novel off-stoichiometric NaxV2(PO4)3 cathode is synthesized, and the effects of compositional variations on both structural stability and electrochemical properties are investigated. Particularly, the optimized Na3.3V2(PO4)3 electrode exhibits superior cycling stability with a capacity retention of 86.7 % after 400 cycles, and excellent rate capability, achieving a capacity of 90 mAh g-1 at 5 C. Through a combination of electrochemical analysis and first-principle calculations, it is elucidated that the excess Na+ content within the structure effectively expands lattice volume, thereby mitigating migration barriers for enhanced ion diffusivity.