Research On The Surface Modification Of Na₃V₂（PO₄）₃/C With Two Typical NASICON Materials

At present,in many electrochemical energy storage technologies,lithium ion batteries quickly occupy the market of innovative energy electric vehicles and portable electronic equipment due to their advantages of high energy density,high power density,and long cycle life.However,lithium sources have limited reserves and uneven distribution,which hinders the application of lithium ion batteries of large-scale energy storage.Sodium ion batteries are expected to become an important development direction for largescale energy storage due to their abundant sodium source reserves,low cost,and similar working principles to lithium ion batteries.Among various positive electrode materials,polyanionic compounds with a sodium fast ion conductor（NASICON）structure have received special attention because this three-dimensional open framework can form a large number of gaps,which is conducive to the rapid deintercalation of Na+ and produces very little lattice strain.Among them,rhombohedral phase Na₃V₂（PO₄）₃ is a typical polyanionic compound with NASICON structure.It has a stable electrochemical platform and exhibits good Na+ storage performance at high and low operating voltages.However,the lower electronic conductivity greatly limits its rate performance and long cycle life,and also affects future large-scale energy storage applications.In recent years,the progress made in the preparation and modification of Na₃V₂（PO₄）₃ mainly includes the development of Na₃V₂（PO₄）₃/carbon-coated（composite）materials and element doping to improve the electronic conductivity of the cathode material Na₃V₂（PO₄）₃ strategies for designing three-dimensional porous structures and nanostructures to enhance the transport of sodium ions.Compared with traditional batteries using liquid electrolytes,all-solid batteries use non-flammable solid electrolytes with good thermal and mechanical stability,which may inhibit the formation of metal dendrites and provide better safety performance and more high energy density,so all-solid-state batteries will become an important direction for the development of next-generation ion batteries,and all-solid-state sodium ion batteries have more development potential due to the rich sodium resources.However,some studies have found that the problem of poor interface contact between the electrode material and the solid electrolyte may cause the reversible capacity of the electrode material to decrease and the capacity to rapidly decay.Therefore,at present,the application of all-solid sodium ion batteries is still in the stage of research and exploration.Based on this background,after the Na₃V₂（PO₄）₃ material is coated with（composite）carbon material,this paper uses the NASICON type material as a surface modifier to directly coat the surface of the Na₃V₂（PO₄）₃/C cathode material without damage the three-dimensional sodium ion transmission channel of the raw material also provides a feasible idea for solving the problem of interface contact compatibility between the solid electrolyte and the positive electrode material.specific research content:1.Select NASICON material Li_1.4Al_0.4Ti_1.6（PO₄）₃ for surface modification of Na₃V₂（PO₄）₃ precursor.Li_1.4Al_0.4Ti_1.6（PO₄）₃ surface decorations and cathode materials were crystallized at the same time through a high temperature calcining treatment to realize the integration of cladding doping.XRD,SEM,TEM and XPS were used to test the changes of Na₃V₂（PO₄）₃/C morphology and structure after surface modification of different contents of Li_1.4Al_0.4Ti_1.6（PO₄）₃.The dynamic and electrochemical properties of Na₃V₂（PO₄）₃/C after modification were analyzed by constant current charge and discharge,multiplier and cyclic voltammetry,among which the electrochemical properties of the electrode material coated with 0.2 wt.% content were the best.The thermal safety and modification mechanism of Na₃V₂（PO₄）₃/C electrode materials after surface modification were investigated by EIS,FTIR and DSC.2.Use NASICON solid electrolyte material Na₃Zr₂Si₂PO₁₂ to modify the surface of the precursor of the positive electrode material Na₃V₂（PO₄）₃,through a high-temperature calcination process,the Na₃Zr₂Si₂PO₁₂ solid electrolyte material is coated on the surface of the positive electrode material,after the Na₃Zr₂Si₂PO₁₂.The solid-solid interface is compatible between the cathode material and the electrolyte.The changes of morphology and structure of Na₃V₂（PO₄）₃/C after surface modification with different contents of Na₃Zr₂Si₂PO₁₂ were tested by XRD,SEM,TEM and XPS.The dynamic and electrochemical properties of the modified Na₃V₂（PO₄）₃/C electrode materials were analyzed by constant current charge and discharge,rate and cyclic voltammetry tests,and the electrode materials with 2 wt.% coating content had the best electrochemical performance.The thermal safety and modification mechanism of electrode materials after surface modification were explored by EIS,FTIR and DSC tests.