Unlocking fast and reversible sodium intercalation in Na₃MnTi(PO₄)₃ cathode toward high performance sodium-ion batteries

Na₃MnTi(PO₄)₃ (NMTP) shows significant potential as a cathode for sodium-ion batteries (SIBs) owing to its multi-electron transfer capability and high theoretical capacity. Nevertheless, its practical application is significantly limited by sluggish ion diffusion and rapid capacity decay, which stem from structural evolution during the sodiation/desodiation process. Herein, an Fe-doping strategy is proposed to reinforce the structural framework and enhance the electrochemical performance of NMTP. Trace Fe doping is found to shorten the M–O (M = Ti and Mn) bond while extending the Na–O bond, effectively minimizing structural fluctuations in NMTP during charge/discharge cycles and enhancing sodium-ion diffusion kinetics. Consequently, the Na₃Mn_0.99Fe_0.02Ti_0.99(PO₄)₃ (NMTP-Fe0.02) cathode demonstrates exceptional rate capability and long-term stability, delivering a high reversible capacity of 153.2 mAh·g⁻¹ at 0.1 C and retaining 99.3 mAh·g⁻¹ after 800 cycles at 5 C, exhibiting a capacity preservation rate of 81.5%. Moreover, its outstanding performance in full-cell configurations highlights the significant potential of NMTP-Fe0.02 for practical applications.