Preparation And Electrochemical Performance Of Cathode Material Na₃V₂（PO₄）₃ For Sodium Ion Batteries

In this paper,NH₄VO₃,Na₂CO₃,NH₄H₂PO₄ and oxalic acid dihydrate were used as raw materials.The Na₃V₂（PO₄）₃ cathode material for sodium ion batteries was successfully prepared by simple hydrothermal method,and the reaction conditions（C₂H₂O₄·2H₂O concentration,hydrothermal time,calcination temperature）of the experiment were optimized;Later,the materials were modified by ion doping and surface coating to improve their electrochemical performance.By electrochemical performance test and XRD,SEM characterization of the sample,it was found that the C₂H₂O₄·2H₂O concentration（0.6 M,0.7 M,0.8 M,0.9 M,1.0 M）,the hydrothermal time（12 h,14 h,16 h,18 h,20 h）and calcination temperature（700℃,750℃,800℃,850℃,900℃）were sequentially changed under the control of other quantities unchanging;when the C₂H₂O₄·2H₂O concentration was 0.8 M,hydrothermal time was 16 h,calcination temperature was 800℃,the obtained Na₃V₂（PO₄）₃ material exhibited a uniform dispersion of the irregular morphology and the best electrochemical performance.when the current density of the test was 0.1 C,the first discharge specific capacity was 92.9 mAh/g,after 100 cycles of the test cycle,the capacity of 60.8 mAh/g can still be released,and the capacity retention rate was 65.5%.Study on Gadolinium doping modification of Na₃V₂（PO₄）₃ by using Gd（NO₃）₃·6H₂O.The Na₃V_2-XGd _X（PO₄）₃（X=0,0.01,0.02,0.03,0.04）was successfully prepared that it can be proved by electrochemical performance test and XRD,SEM,EDS characterization of the sample.The electrochemical performance test of Na₃V_2-XGd_X（PO₄）₃ material showed that the Na₃V_1.97Gd_0.03(PO₄3))3 material exhibited the best electrochemical performance.when the current density was 0.1 C.The capacity is110.3 mAh/g,the Na₃V_1.97Gd_0.03（PO₄）₃ material can still released 85.7 mAh/g after 100cycles under 0.1 C test conditions.it was significantly higher than the discharge specific capacity of other materials of the same series under the same conditions.Study on MgO coating modification of Na₃V₂（PO₄）₃ by using Mg（CH₃COO）₂·4H₂O,the electrochemical performance test and XRD,SEM,TEM,EDS characterization of the sample can prove that the NVP@XMgO（X=0.0%,3.0%,3.5%,4.0%,4.5%,5.0%）series materials have been successfully prepared.The electrochemical performance test of NVP@XMgO material showed that when the current density of the test was 0.1 C,NVP@4.0%MgO exhibited the best electrochemical performance and high discharge capacity,all higher than the discharge specific capacity of other materials under the same conditions;when the test current returns to 0.1 C during the rate test The specific discharge capacity was 116.6 mAh/g,and the recovery rate was 90.5%.