Abstract:

The polyanionic Na₃（VOPO₄）₂F material has the characteristics of structural stability，high safety，and high operating voltage.Its open three-dimensional framework structure can provide a pathway for the rapid migration of sodium ions，making it one of the most promising cathode electrode materials for sodium ion batteries at present.However，the rate performance of Na₃V₂（PO₄）₂O₂F is unsatisfactory because of its poor intrinsic electronic conductivity.Ion doping is an effective strategy for improving the conductivity and electrochemical performance of this material.S^2--doped Na₃（VOPO₄）₂S _x F was successfully prepared by adding appropriate amounts of thioacetamide in the hydrothermal process.X-ray diffraction and electrochemical impedance spectroscopy results indicated that the doping of S^2- could expand ion diffusion channels and reduce charge transfer resistance.The results of galvanostatic intermittent titration technique proved that S^2- doping could accelerate ion migration rate.Thus，the Na₃（VOPO₄）₂S _x F delivered an excellent electrochemical performance in the sodium ion half-cell，showing a capacity of 66.8 mA·h/g at 30C and retaining 96% of its capacity after 500 cycles at 10C.A sodium ion full cell coupled with the Na₃（VOPO₄）₂S _x F cathode and hard carbon anode delivered a high capacity of 121.7 mA·h/g，and the capacity loss after 60 cycles at 1C could be ignored.

Key words: Na₃（VOPO₄）₂F, ion-doping, cathode material, sodium ion batteries