Effect of Ti-doping on the electrochemical performance of sodium vanadium(iii) phosphate.

Na3V2-x Ti x (PO4)3 (x = 0.00, 0.05, 0.10, and 0.15) was successfully synthesized by a conventional solid-state route. The XRD results show that Ti is incorporated in the lattice of Na3V2(PO4)3 and the tetragonal structure has not been changed after doping. Among all the composites, the Na3V1.9Ti0.1(PO4)3 composite delivers the highest discharge capacity of 114.87 mA h g-1 at 0.1C and possesses a capacity retention of 96.23% after 20 cycles at 0.1C, demonstrating the better rate performance and cycle stability in the potential range of 2.0-3.8 V. Electrochemical impedance spectroscopy (EIS) results reveal that the Na3V1.9Ti0.1(PO4)3 composite has a lower charge transfer resistance and a higher Na-ion diffusion coefficient compared to other composites. The results indicate that Ti-doping in Na3V2(PO4)3 can effectively enhance the electrochemical performance of this tetragonal compound, especially at a high charge/discharge rate.