Unlocking fast and reversible sodium intercalation in Na 3MnTi(PO 4) 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 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 Na3Mn0.99Fe0.02Ti0.99(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.