Superior conductivity and accelerated kinetics Na3V2(PO4)2F3@CNTs with high performance for sodium-ion batteries

Na3V2(PO4)2F3 with a high theoretical energy density, robust 3D structure, and superior thermal stability has become one of the popular cathode materials for sodium ion batteries. Currently, its poor intrinsic electronic conductivity leads to unsatisfactory rate performance, which is still the bottleneck for commercializing sodium-ion batteries. In this work, carbon nanotube–intertwined Na3V2(PO4)2F3 nanospheres (notated as NVPF@CNTs) are successfully synthesized by a solvothermal method and subsequent heat treatment. In NVPF@CNTs composites, the carbon nanotubes constituted a continuous conductive 3D carbon network, realizing the improvement of electrical conductivity. The NVPF nanospheres are exposed to the electrolyte to increase the contact area with the electrolyte and greatly shorten the diffusion distance of Na+. The unique architecture endorses superior electrochemical performance and good reaction kinetics. Thus, the NVPF@CNTs as cathode exhibits good cycling performance (117.6 mAh g−1 at 0.2 C after 300 cycles) and rate capability (73.4 mAh g−1 at 5 C with a high capacity retention ratio of 91.6% after 600 cycles). The excellent electrochemical performance for NVPF@CNTs opens up a new way to achieve high performance of sodium-ion batteries.