Facial construction of high rate Na3V2(PO4)2F3/C microspheres with fluorocarbon layer by deep-eutectic solvent synthesis

Porous Na3V2(PO4)2F3 (NVPF) with micro-nano structure was prepared by a simple deep-eutectic solvent method with good crystallinity and uniformity. Surface modification was used to produce carbon-coated NVPF (NVPF/C). The unique morphologic architecture and surface modification improve the structural stability and interfacial chemical stability of NVPF, ensuring the excellent rate performance and cycle stability of NVPF/C. At 120 °C, secondary microspheres NVPF composed of nanoparticles are successfully synthesized. By liquid phase reaction in a deep-eutectic solvent X-ray diffraction analysis reveals that these microspheres have good crystallinity. The NVPF/C with an amorphous fluorocarbon coating layer is constructed by pyrolysis of polytetrafluoroethylene (PTFE). The mesoporous structure and the existence of the coating layer are clearly obvious under the high-definition transmission electron microscope. The amorphous fluorocarbon layer enhances the reversibility and transmission ability of Na+, improving the electrochemical kinetics. And the obtained NVPF/C cathode material displays high-rate performance. The as-prepared NVPF/C-F composites with 6 %wt coating of PTFE have a specific capacity of 110.6 mAh g−1 at 10 C, 106.4 mAh g−1 at 20 C and 94.6 mAh g−1 at 50 C. The capacity retention rate is 90.4 % after 700 cycles at 20 C. This research provides a facile and inexpensive approach for getting high-rate performance sodium-ion battery cathode materials.