Enhanced electrochemical performance of Na3V2(PO4)(3) with Ni2+ doping by a spray drying-assisted process for sodium ion batteries

Spherical Na3V2-xNix(PO4)(3)/C composites with different Ni2+ doping contents (x = 0, 0.05, 0.1, 0.15, 0.2) were prepared through a spray drying-assisted method for sodium batteries. The XRD analysis indicates that a small amount of Ni2+ doping does not alter the structure of Na3V2(PO4)(3)/C. SEM demonstrates that the particle size of spherical Na3V2-xNix(PO4)(3)/C materials are 1-2 mu m. The four-point probe method and electrochemical impedance spectroscopy (EIS) show that the Ni2+ doped Na3V2(PO4)(3)/C samples possess higher electronic conductivity and smaller charge transfer resistance compared with the undoped Na3V2(PO4)(3)/C cathode composite, which is favorable for improving the cell performance. Especially for the Na3V1.85Ni0.15(PO4)(3)/C, it exhibited a superior discharge capacity of 104.5 mAh.g(-1) at a high rate of 5C. Moreover, after 1000 cycles at 5C, an excellent capacity retention of 95.4% is maintained.