Study Of Modification Sodium Vanadium Phosphate Cathode Material

In this paper,Na₃V₂?PO₄?₃ was used as the basic material.Chemical synthesis method was used to synthesize materials through carbon coating,non-metallic doping and other modification measures.The influence of the synthesis process,composition and structure on the properties were explored.The cathode material of Na₃V₂?PO₄?₃/C with excellent electrochemical properties was synthesized successfully.The composite material of Na₃V₂?PO₄?₃/C was synthesized by hydrothermal treatment using sodium alginate as template and carbon source.The carbon skeleton structure formed by the calcination of sodium alginate has excellent mechanical strength,so that it can maintain stability without collapse when charging and discharging under high current density,and improve the cycle performance and rate performance of the material.Through electrochemical tests,it was known that when 50 m L of sodium alginate aqueous solution was added,the electrochemical performance of the material was the best.The discharge capacity was 110.3 m Ah g^-1 at 0.5 C.When the rate was increased to 50 C after 1 000 cycles.the capacity retention rate was 46.3%,and the coulombic efficiency was close to 100%.NVP/C composites were prepared by sol-gel method using C₄H₆O₆ as carbon source and tempalte.Tartaric acid is an organic acid material extracted from plants.Tartaric acid will generate a large number of pores after calcination due to gas overflow at high temperature.These pores are beneficial to the transmission of sodium ions and promote the penetration of electrolyte.Through electrochemical tests,it was known that the synthesized NVP material had the good performance when the amount of C₄H₆O₆was 3 mmol and the calcination temperature was 800^oC.The discharge capacity was118.7 m Ah g^-1 at 0.1 C,which was slightly higher than the theoretical specific capacity of NVP.When the rate was increased to 100 C,the discharge capacity was 67.5 m Ah g^-1at first cycle,and the discharge capacity was 57.3 m Ah g^-1 after 1 000 cycles.It had excellent cycle performance and multiplier performance.It also proves that the carbon skeleton structure formed by the calcination of C₄H₆O₆ can effectively improve the electrochemical performance of NVP materials.The composite material of the N-H doping NVP/HC was synthesized by hydrothermal treatment using Soybean flour as nucleating agent and carbon source.Through electrochemical tests,it was known that when 6 g soybean flour was added and the calcination temperature was 800^oC,the synthesized NVP/HC material had the best performance.And the discharge capacity was 121.5 m Ah g^-1 at 0.5 C,104.3m Ah g^-1 at50 C,59.5 m Ah g^-1 at 8 000 cycles.It had excellent cycle performance and multiplier performance.Na_3+xV₂?PO₄?_3-x?Si O₄?_x/C composite materials with excellent electrochemical performance was successfully synthesized by sol-gel method.When the x=0.3,the material of NVPSi/C had the best performance.And the discharge capacity reaches 117.6 m Ah g^-1 at 0.1 C,98.2 m Ah g^-1 at 50 C and 87.5 m Ah g^-1 at 50C after 500 cycles.It had excellent cycle performance and multiplier performance.The capacity retention rate was 88.7%.This indicates that the Na_3.3V₂?PO₄?_2.7?Si O₄?_0.3/C composite material formed by doping an appropriate amount of Si had excellent electrochemical performance.