Preparation and sodium storage properties of sulfur-doped Na3(VOPO4)2F cathode materials
The polyanionic Na3(VOPO4)2F material has the characteristics of structural stability,high safety,and high oper-ating 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 perfor-mance 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.S2--doped Na3(VOPO4)2SxF 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 S2-could expand ion diffusion channels and re-duce charge transfer resistance.The results of galvanostatic intermittent titration technique proved that S2-doping could ac-celerate ion migration rate.Thus,the Na3(VOPO4)2SxF 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)2SxF 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.
Na3(VOPO4)2Fion-dopingcathode materialsodium ion batteries
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