Preparation And Properties Of Na₃V₂?PO₄?₃/C Cathode Material For Sodium-ion Batteries

In the face of the urgent development of large-scale charging energy storage technology,sodium ion battery has become a promising way of energy storage.In recent ten years,a lot of research has been done on NIBS cathode materials with large size tunnel structure and fast ion diffusion channel,among which polyanionic compounds with open three-dimensional frame structure have attracted much attention.Na₃V₂?PO₄?₃ with typical three-dimensional?3D?NASICON structure has been widely used because of its high ionic conductivity,but its poor electronic conductivity limits its application.In this paper,carbon-coated sodium vanadium phosphate was synthesized by different synthesis methods and modified to enhance the conductivity of sodium vanadium phosphate.The specific studies are as follows:?1?Carbon coated sodium vanadium phosphate was synthesized by a simple and easy to operate solid phase ball milling method.the modification of sodium vanadium phosphate was realized and the electrochemical properties of the material were improved.The initial discharge capacity of Na₃V₂?PO₄?₃/C synthesized by solid phase method is 71.39 mAh g^-1 at 5 C high current density,and the capacity retention rate of1000 cycles is 72.3%.The Coulomb efficiency is kept at about 100%,showing good electrochemical performance?2?Na₃V₂?PO₄?₃/C was synthesized by sol-gel method,and the effects of different carbon content on the electrochemical properties of the materials were investigated.It is found that the electrode material has the best electrochemical performance when the ratio of vanadium source to carbon source is 1:1.The electrode can emit a capacity of108.60 mAh·g^-1 at a current density of 0.5 C,and the capacity retention rate is 94.2%after 100 cycles.After 1000 cycles of 10 C cycle,the capacity rates was 85%.?3?Carbon-coated sodium vanadium phosphate was synthesized by hydrothermal assisted sol-gel method.The unique morphology of NVP particles embedded in carbon pores is formed by adding polyvinylpyrrolidone?PVP?,The reversible capacity of Na₃V₂?PO₄?₃/C material prepared by adding PVP at 1 C current density is 110.69 mAh g^-1,and the capacity retention rate is 94.5%after 1000 cycles at 10 C current density.?4?In this chapter,flake stacked Na₃V₂?PO₄?₃/C composites were synthesized by PVP combined with hydrothermal method for the first time.the nano-sheets were connected and overlapped with each other to form a suitable carbon coating and nano-plate structure.The reversible capacity of the material is 106.42 mAh·g^-1 at 0.2 C current density and 104 mAh·g^-11 after 100 cycles,with a capacity retention rate of 97.7%.