Preparation And Doping Modification Of Sodium Vanadium Phosphate

Na₃V₂（PO₄）₃as the cathode material of sodium ion battery,has stable three-dimensional（3D）NASICON structure,Its theoretical specific capacity is117.6m Ahg^-1.The working voltage is about 3.4V,which is one of the cathode materials of sodium ion battery.However,the discharge capacity of sodium vanadium phosphate synthesized directly is low and its decay is serious with the increase of cycle period,which limits its practical order to solve this problem,in this paper,Na₃V₂（PO₄）₃as the research object,using hydrothermal method to prepare carbon coated Na₃V₂（PO₄）₃/C composite cathode material,explore its optimal calcination temperature and improve the electrochemical performance of Na₃V₂（PO₄）₃/C by doping as to find the best Na₃V₂（PO₄）₃/C composite cathode material,and on this basis,increase its load to make high load battery.In this paper,the electrochemical properties of Na₃V₂（PO₄）₃all-sodium battery were specific content includes the following aspects:（1）Na₃V₂（PO₄）₃was synthesized by hydrothermal method.The optimal calcination temperature was found to be 750℃by changing the calcination temperature,at this temperature,Na₃V₂（PO₄）₃electrochemical properties are good:the discharge specific capacity reaches 92.27m Ahg^-1at 0.5C,and the capacity retention rate is 96.67%for 1000 cycles at 5C,showing excellent cycling performance.（2）Na₃V₂（PO₄）₃calcined at 750℃was doped with F,Cl and Br in different proportions was carried out to obtain the optimal doping F and Cl,while the expected results were not obtained with Br doping.The products doped with 0.01F and 0.05Cl were compared with the Na₃V₂（PO₄）₃of 750℃calcination get better doping products,the ratio performance of 0.01F doped Na₃V₂（PO₄）₃was the best.The specific discharge capacity reaches 100.36m Ahg^-1at 0.5C.（3）Different amount of chitosan was used as carbon source to explore its influence on material properties.The optimum amount of chitosan was 25%of the mass of synthesized Na₃V₂（PO₄）₃,and the viscosity of the chitosan was less than200m P.s.On this basis,the optimum calcination temperature is 800℃,and the discharge specific capacity reaches 98.02 m Ahg^-1at 0.5C.The specific discharge capacity at 5C is 97.45m Ahg^-1,and the capacity retention rate is 97.72%in 260cycles.（4）Using sodium vanadium phosphate with chitosan as carbon source to produce high load to improve specific energy,and using sodium vanadium phosphate as positive electrode and sodium titanium phosphate as negative electrode to assemble complete battery to explore its electrochemical performance make it closer to practical application.