锂离子电池复合正极材料Li3-2xMgxV2（PO4）3/C的合成及其电化学性能

摘要

采用溶胶−凝胶法制备Li3−2xMgxV2(PO4)3/C (x=0、0.01、0.03、0.05)复合材料，并通过X射线衍射(XRD)、扫描电镜(SEM)和电化学测试等测试手段对合成材料进行表征。XRD 结果表明：在 Li3V2(PO4)3的锂位掺杂少量Mg2+，并没有明显改变Li3V2(PO4)3晶体的单斜结构，但镁掺杂Li3V2(PO4)3的晶胞体积大于未掺杂Li3V2(PO4)3的晶胞体积。所有镁掺杂复合材料Li3−2xMgxV2(PO4)3/C (x=0.01、0.03、0.05)的电化学性能均优于Li3V2(PO4)3/C复合材料，其中，Li2.94Mg0.03V2(PO4)3/C 在上述所有材料中具有最高的容量和最好的循环性能。对 Li3V2(PO4)3/C 和Li2.94Mg0.03V2(PO4)3/C的锂离子扩散系数及电化学性能进行对比分析，结果表明：Li+在镁掺杂Li3V2(PO4)3材料中的快速扩散是由Mg2+在锂位的掺杂造成，Li+在活性材料中的快速扩散使镁掺杂Li3V2(PO4)3材料具有优良的电化学性能。%The Li3−2xMgxV2(PO4)3/C (x=0, 0.01, 0.03 and 0.05) composites were prepared by a sol−gel method and characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and electrochemical measurements. The XRD results reveal that a small amount of Mg2+ doping into Li sites does not significantly change the monoclinic structure of Li3V2(PO4)3, but Mg-doped Li3V2(PO4)3 has larger cell volume than the pristine Li3V2(PO4)3. All Mg-doped composites display better electrochemical performance than the pristine one, and Li2.94Mg0.03V2(PO4)3/C composite exhibits the highest capacity and the best cycle performance among all above-mentioned composites. The analysis of Li+ diffusion coefficients in Li3V2(PO4)3/C and Li2.94Mg0.03V2(PO4)3/C indicates that rapid Li+ diffusion results from the doping of Mg2+ and the rapid Li+ diffusion is responsible for the better electrochemical performance of Mg-doped Li3V2(PO4)3/C composite cathode materials.