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

Na₃V_2- Ti (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 Na₃V_1.9Ti_0.1(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 Na₃V_1.9Ti_0.1(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.