Controllable Preparation And Sodium Storage Properties Of Fluorinated Sodiums Vanadium Phosphate Composite Nanostructures

Energy storage has become a key issue in our daily lives.In a variety of energy storage technologies,secondary batteries are one of the most important and promising options.Lithium ion batteries?LIB?have surpassed other rechargeable batteries in mobile applications and portable devices due to their high energy density,high voltage,and environmental friendliness.However,with the growing demand for fixed energy storage,the insufficient lithium reserves on the planet will not be able to support the huge consumption of the future market.Sodium ion batteries?SIB?and lithium ion batteries have similar working principles and the rich sodium reserves in the earth's crust.It is generally considered one of the most promising LIB to replace the new rechargeable battery system,at the same time,the development of cathode materials is particularly important.Among the many cathode materials of sodium ion batteries studied today,Na₃V₂O_2x?PO₄?₂F_3-2x?0?x?1?with high voltage and theoretical energy density has attracted extensive attention and research as a cathode material for sodium ion batteries.Therefore,based on the morphological structure of Na₃V₂O_2x?PO₄?₂F_3-2x,combined with the performance improvement and promotion methods of the three main electrode materials of cladding,doping and compounding with carbon materials,three different morphologies of fluorination were synthesized Vanadium phosphate sodium composite material,and the effect of different morphologies combined with different performance enhancement methods on the electrochemical performance of the material,was designed to develop a practical Na₃V₂O_2x?PO₄?₂F_3-2x-2x composite cathode material.The specific research content is as follows:?1?Four different morphologies of Na₃V₂O₂?PO₄?₂F?x=1?were synthesized by polyol-assisted hydrothermal method using four different organic solvents.Through electrochemical tests,it was found that flake Na3V2O2?PO4?2F showed better electrochemical performance.At the same time,the surface of flaky Na₃V₂O₂?PO₄?₂F material was coated with TiO2-x with different content of oxygen defects by sol-gel method and high-temperature calcination.The test results show that Na₃V₂O₂?PO₄?₂F@TiO_2-x-x composites with TiO_2-x-x content of about 3 wt%show the best cycle performance and rate performance.?2?The Mn-doped Na₃V_2-xMn_xO₂?PO₄?₂F hollow nanospheres were synthesized using a polyol-assisted hydrothermal method,and the XRD,XPS,ICP and mapping characterization analysis confirmed the successful doping of Mn(Mn²⁺/Mn³⁺).At the same time,by changing the reaction time and the amount of H₂O₂,the formation process of hollow nanospheres and the effect of H₂O₂ on the morphology of the materials were studied.And the electrochemical test found that compared with pure Na3V2O2?PO4?2F?x=1?materials,the electrochemical performance of Mn-doped Na₃V_2-xMn_xO₂?PO₄?₂F composites has been significantly improved,especially at high rates.?3?Hollow Na₃V₂?PO₄?₂F@C microspheres composed of primary nanosheets were successfully synthesized by polyol-assisted hydrothermal method.By mixing it with graphene oxide at high temperature and firing at high temperature,Na₃V₂?PO₄?₂F@C@rGO composite material encapsulated by redox graphene was successfully obtained.At the same time,by changing the reaction time and the ratio of triethylene glycol to water and the amount of added glucose,the growth and formation process of hollow microspheres was systematically studied and explored.And the electrochemical test shows that when the amount of graphene oxide compounded is 10 wt%,the Na₃V₂?PO₄?₂F@C@rGO composite material shows the best electrochemical performance.