Benefits of vanadium doping in Na₃MnTi(PO₄)₃/C as a potential candidate for sodium-ion batteries

Na₃MnTi(PO₄)₃/C is a high-energy sodium-ion battery (SIBs) cathode material. However, the low rate performance and unfavorable cycle life limit its practical applications. Herein, Na₃Mn_1-xV_xTi(PO₄)₃/C (x = 0, 0.01, 0.05, 0.10) were synthesized by a facile sol-gel method and the performance has been researched via the difference of vanadium doping amount. X-ray diffraction (XRD) indicates that vanadium doping has no obvious effect on the crystal structure. X-ray photoelectron spectroscopy (XPS) and Energy dispersive X-ray spectroscopy (EDS) mapping images show that vanadium has been successfully doped into the material. Cyclic voltammogram (CV) displays obviously three pairs of redox couples, corresponding to the Ti³⁺/Ti⁴⁺, Mn²⁺/Mn³⁺ and Mn³⁺/Mn⁴⁺ redox couples, respectively, and is mainly controlled by diffusion and exhibits pseudo-capacitance behavior. The experimental results indicate that vanadium doping can improve the electrochemical performance of Na₃MnTi(PO₄)₃/C, the high specific capacity (116.5 mAh g⁻¹ with a coulomb efficiency of 100% at 0.2C after 100 cycles, 91.8 mAh g⁻¹ higher than that of undoped sample), outstanding cyclability (≈73.6% capacity retention after 500 cycles at 1C, 58.3% higher than that of undoped sample) for Na₃Mn_0.95V_0.05Ti(PO₄)₃ make the vanadium doping become a promising modification method.