硫掺杂Na_(3)(VOPO_(4))_(2)F正极材料的制备及储钠性能

Preparation and sodium storage properties of sulfur⁃doped Na_(3)(VOPO_(4))_(2)F cathode materials

聚阴离子型Na_(3)(VOPO_(4))_(2)F材料具有结构稳定、安全性高及工作电压高等特性,其开放的三维框架结构可以为钠离子的快速迁移提供路径,是目前最具发展潜力的钠离子电池正极材料之一。然而,Na_(3)(VOPO_(4))_(2)F的本征电子导电性较差,导致倍率性能不理想。离子掺杂是一种提升材料导电性和电化学性能的有效策略。通过水热法成功制备了S^(2-)掺杂的Na_(3)(VOPO_(4))_(2)S_(x)F材料。XRD和电化学阻抗结果表明,S^(2-)掺杂可以扩大离子扩散通道并降低电荷传输电阻;恒电流间歇滴定测试结果显示S^(2-)掺杂可以加快离子迁移速率。因此,Na_(3)(VOPO_(4))_(2)S_(x)F正极材料在钠离子半电池中表现出优异的电化学性能,在30C倍率下可逆比容量为66.8mA·h/g,在10C倍率下循环500次后容量保持率可达96%。Na_(3)(VOPO_(4))_(2)S_(x)F正极与硬碳负极组成的钠离子全电池可获得121.7mA·h/g的高比容量,在1C倍率下循环60次后,其容量衰减可以忽略不计。

The polyanionic Na_(3)(VOPO_(4))_(2)F 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 Na_(3)V_(2)(PO_(4))_(2)O_(2)F 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 Na_(3)(VOPO_(4))_(2)S_(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 Na_(3)(VOPO_(4))_(2)S_(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 Na_(3)(VOPO_(4))_(2)S_(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.