N-Doped Carbon Nanotubes Decorated Na₃V₂(PO₄)₂F₃ as a Durable Ultrahigh-rate Cathode for Sodium Ion Batteries

Na₃V₂(PO₄)₂F₃ (NVPF) is emerging as one of the most prospective cathodes for sodium ion batteries due to its robust structure, rapid diffusion of sodium ions, and high energy density. However, the poor electronic conductivity leads to unsatisfactory rate capability and insufficient cyclability. Herein, the meticulous design and preparation of NVPF particles anchored on N-doped carbon nanotubes is realized via a plain sol-gel method. It demonstrates that a N-doped carbon nanotubes matrix can evidently boost the electronic/ionic conductivity of the material and promote the charge transfer between the electrode and electrolyte interface. Moreover, the patulous surface decorated with CNTs leads to the significant contribution of pseudocapacitance effect. Consequently, the electrochemical characteristics of this NVPF particles in a N-doped electron-rich matrix are significantly enhanced, exhibiting a capacity of 126 mA h g^-1 at 0.5 C and ultrahigh-rate capability of 76 mA h g^-1 at 100 C. Besides, an impressive capacity retention of 60.4% upon long-term cycling (1500 cycles) at a high rate of 40 C is also achieved.