Nitrogen-doped carbon encapsulated NaVPO4F as a promising ultra-long stability cathode for sodium ion batteries

Polyanion-type sodium fluorovanadium phosphate (NaVPO 4 F) has been regarded as a distinguished cathode material for sodium-ion batteries, attributed to its elevated working potential and theoretical specific capacity. However, its practical rate property and cycling stability are still challenged due to poor electronic conductivity. Herein, the nitrogen-doped carbon encapsulated NaVPO 4 F (NaVPO 4 F/NC) material was fabricated by the hydrothermal method . N-doping modulates the carbon's electronic structure by introducing “topological defects,” thereby enhancing ion and electron transport kinetics. The NaVPO 4 F/NC cathode demonstrates superior initial discharge capacities of 134.1 mAh/g and 125.1 mAh/g at 1C and 5C, respectively. Additionally, it exhibits outstanding ultra-long stability, retaining the discharge capacity of 105.3 mAh/g at 5C even after 3000 cycles, with an impressive loss rate of only 0.011 % per cycle from 1000th to 3000th cycles. Density functional theory (DFT) revealed the mechanism of N-doped carbon enhanced electrochemical performance. N-doped carbon significantly boosted the material's conductivity and facilitated Na + adsorption and diffusion, thereby accelerating Na-storage and reaction kinetics. These findings suggest that N-doping carbon is an effective strategy to enhance the conductivity of the materials, consequently hence the electrochemical performance. This simple strategy of non-metal doped carbon-coated could facilitate commercial application for NaVPO 4 F materials and expand the choice of cathodes for sodium ion batteries .