N‑Doped\nCarbon Nanotubes Decorated Na₃V₂(PO₄)₂F₃ as a Durable\nUltrahigh-rate Cathode for Sodium Ion Batteries

Abstract

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