Abstract:

To improve the conductivity and high rate charge-discharge performance of Na₄Fe₃（PO₄）₂P₂O₇/C（NFPP） cathode material for sodium ion batteries，Mo-Mn dual doped and composite carbon nanotubes（CNTs） modified NFPP materials were prepared by spray drying.The structure and properties of modified NFPP materials were analyzed using X-ray diffraction（XRD），scanning electron microscopy（SEM），transmission electron microscopy（TEM），galvanostatic intermittent titration technique（GITT），and other physical and electrochemical testing techniques.The results indicated that compared to Mo⁶⁺-doped sample，the synergistic dual doping of Mo⁶⁺ and Mn²⁺ could further reduce the charge transfer impedance，improve the sodium ion diffusion coefficient，and enhance the electrochemical performance.The reversible capacities of Na₄Fe_2.87Mo_0.1Mn_0.03（PO₄）₂P₂O₇/C material at 0.1C，5.0C，and 10.0C rates were 122.6，100.3，and 95.6 mA·h/g，respectively.After further composite modification with 5% CNTs，the charge transfer impedance was further reduced to 313 Ω，and the sodium ion diffusion coefficient was increased to 4.23×10^-10 cm²/s，further improving the rate performance and cycling performance.Its reversible capacities at 0.1C，5.0C，and 10.0C rates were increased to 123.0，109.5，and 104.4 mA·h/g，respectively，and the capacity retention after 350 cycles at 10.0C rates was as high as 92.52%.This study indicated that Mo-Mn dual doping and carbon nanotubes composite modification were effective strategies for improving the electrical performance of NFPP，providing important theoretical and experimental basis for the development of high⁃performance cathode materials for sodium ion batteries.

Key words: sodium ion batteries, Na₄Fe₃（PO₄）₂P₂O₇/C, Mo-Mn dual doping, carbon nanotubes