Alleviating the Potential Hysteresis of Na_3.5MnCr_0.5Ti_0.5(PO₄)₃ Through Mo-Doping for High-Rate Sodium-Ion Batteries

Na_3.5MnCr_0.5Ti_0.5(PO₄)₃ (NMCrTP) demonstrates significant development potential as a cathode material for sodium-ion batteries owing to its low cost and high discharge plateau. However, the severe potential hysteresis phenomenon caused by Mn·Na anti-site defects (Mn·Na-ASD) of Mn²⁺ residing in Na vacancies is hindering its performance release. Here, a strategy is proposed to alleviate the anti-site defects in NMCrTP through doping Mo at the Ti sites using the sol-gel method. Rietveld refinement results confirm that the content of Mn·Na-ASD decreases from 6.30% in NMCrTP/C to 0.98% in NMCrTP/C-0.05Mo. Meanwhile, Hall effect measurements verify that the Mo donor induces the carrier-type transformation from p-type to n-type, enhancing electronic conductivity from 3.07 × 10^-3 to 3.61 × 10^-3 S cm^-1. Moreover, the ion diffusion coefficient measured by GITT increases from 3.96 × 10^-12 to 1.34 × 10^-11 cm²/s. In result, the mean discharge potential of the NMCrTP/C-0.05Mo cathode increases from 2.62 V (vs. Na⁺/Na) to 3.47 V, and the electrochemical polarization decreases from ΔV = 0.20 to 0.09 V. As expected, the NMCrTP/C-0.05Mo cathode delivers an excellent rate performance of 88.4 mAh g^-1 at a high rate of 10 C. This work presents an effective strategy to alleviate the potential hysteresis of the NMCrTP cathode for high-rate SIBs.