The Microstructure-controlled Synthesis Of Sodium Vanadium Phosphate And Its Application For Sodium-ion Batteries

Lithium ion batteries?LIBs?have been widely used in portable electronic market as efficient energy storage devices,and that have expanded to electric vehicles,smart grids and a large scale renewable energy storage system.However,lithium resource deficiency on the earth as well as the wide application of LIBs are not suitable for large-scale energy storage.So the development of low cost,long life,high safety of new type energy storage devices is imminent.Sodium-ion batteries?NIBs?are a promising alternative to LIBs for large-scale energy storage applications,because of the high availability of sodium,its low cost,and the similarity in the intercalation chemistry of sodium and lithium.Sodium phosphate[Na3V2?PO4?3?NVP?]has an open three-dimensionnal?3D?framework,which is constructed with via XO4?X=P,S,Si,As,Mo,W,etc.?tetrahedron and MO6?M is transition metal?octahedron through common angle or common edge connection.It has a NASICON-type framework structure,larger sodium storage sites,a high operating voltage and a high energy storage capacity.As a result,it should be a suitable cathodic material for SIBs.In this study,the carbon coating technology and metal ion doping,are used to improve the electrical conductivity of this material,thus resulting in excellent electrochemical performance.In this thesis,we synthesized Na3V2?PO4?3/C and Na3V2-xCux?PO4?3/C by combining the hydrothermal method with freeze drying technology.The structure and phase composition were characterized by X-ray power diffraction?XRD?,scanning electron microscopy?SEM?,and transmission electron microscopy?TEM?.In order to test the electrochemical properties under different conditions,we assemble the as-prepared materials with sodium metal piece into half-cell.The main research resuls are as follows:?1?Synthesis of Na3V2?PO4?3/C by combining the hydrothermal method with freeze drying technology.Na3V2?PO4?3/C was prepared via the hydrothermal method followed by freeze drying technology.We regulate and adjust the microstructure of NVP by adjusting the dosage of reagents and reaction temperature.We compared the battery performance of the 3D macroporous NVP and bulk NVP.After 100 cycles,the as-prepared electrodes deliver a high specific capacity of 91.8 mA h g^-1 at a current density of 100 mA g^-1.Compared with various electrochemical properties,the results indicate that the current method has a greater influence on the improvement of material properties.Therefore,Na3V2?PO4?3 is promising cathode material for NIBs.?2?Synthesis of Na3V2-xCux?PO4?3/C under the hydrothermal method combined with freeze drying technology.Metal ion doping can improve the electronic conductivity of the material through lattice replacement to produce defects.Na3V2-xCux?PO4?3/C was prepared via the hydrothermal method combining the freeze drying technology.We studied the effect of different citric acid amount and the copper doping amount on the battery performance.Na3V2-xCux?PO4?3/C delivers a high specific capacity of 105 mA h g^-1 at a current density of100 mA g^-1 after 100 cycles as the cathode material and a high specific capacity of 99.7 mA h g^-1 at a current density of 1 A g^-1.The Na3V2-xCux?PO4?3/C composite also exhibits excellent rate performance and cycling stability.