An Investigation On The Synthesis And Modification Of Li₃V₂（PO₄）₃/C Cathode Material For Lithium-ion Battery

Monoclinic Li₃V₂（PO₄）₃with the fast ion conductivity has recently attracted thetremendous attention from worldwide researchers due to its stable structure, goodcycle performances, low cost and safety. However, the relative low electronicconductvity restricts the high rate performance of Li₃V₂（PO₄）₃and its practicalapplication is severly hindered. Based on the investigation of the recently researchworks about the Li₃V₂（PO₄）₃, in the article, we have adopted four kinds of methods tosynthesize Li₃V₂（PO₄）₃/C composite to solve the problem of low electronicconductivity. Additionally, the full-cell performance is studied with the use ofLi₃V₂（PO₄）₃/C as cathode, graphite carbon and Li4Ti5O12as anode, respectively.The carbon-thermal reduction method is used to fabricate Li₃V₂（PO₄）₃/Ccomposite. After investigation of the different synthesis factors, the optimalelectrochemical performance is obtained and the synthesis parameters are shown infollow: the ball-material ratio of10:1, the sinter temperature of800°C, the sinter timeof8h and the amount of citric acid of0.02mol. Furthermore, polyamide is firstlyintroduced as the carbon source and milling additive into the preparation ofLi₃V₂（PO₄）₃/C with two-step synthesis route. The electrochemical performancesindicate that the as-prepared material can still deliver high discharge capacities of119.52mAh g^-1and112.70mAh g^-1after100cycles at5C and10C rates,respectively.The Li₃V₂（PO₄）₃/C composite is also prepared by the use of sol-gel method. Theoptimal synthesis condition is the pH of7, sinter temperature of850°C, sinter time of8h and citric acid amount of0.018mol. In order to improve the electrochemicalcharacteristics of Li₃V₂（PO₄）₃/C, we separately investigates the effect of Na+and Cl-doping on the properties of Li₃V₂（PO₄）₃/C. The results show that the Na+doping caneffectively improve the diffusion resistance of Li+and Cl-doping can strengthen thestructure stability of PO43-.A novel self-catalyzed sol-gel method is firstly reported with distilled water as theself-catalyzer to synthesize Li₃V₂（PO₄）₃/C composite. The particle size of thesynthsized Li₃V₂（PO₄）₃ranges from0.5μm-1.5μm; There is an uniform carbon layercoated on the particle with the thickness of4nm; The as-prepared material exhibits excellent electrochemical capability of115.72mAh g^-1at10C rate and good cyclestability. On the other hand, multi-walled carbon nanotubes （MWCNTs） are adoptedas electronic conductive medium and ascorbic acid is used as reductive agent toprepare MWCNTs@LVP/C composite under the sol-gel method. With the existence ofMWCNTs, the infulence of various V₂O₅/ascorbic acid ratios on the morphology ofthe MWCNTs@LVP/C composite is also studied.The sol-microwave method is fisrtly introduced to the preparation ofLi₃V₂（PO₄）₃/C. With the low power of320W and short time of12min, thesynthesized Li₃V₂（PO₄）₃/C displays good structure stability and low polarization. Thespecific discharge capacity of100mAh g^-1can still be obtained under the highcharge/discharge rate of20C. Furthermore, the Li₃V₂（PO₄）₃/C with ultrahighdischarge capacity （50C） is firstly synthesized by an in-situ copolymerization with theuse of acrylamide as polymer monometer, N,N’-methylenebisacrylamide ascrosslinking agent and ammonium persulfate as initiator. And the electrochemicalperformances of the Li₃V₂（PO₄）₃/C are investigated in detials.Finally, the electrochemical performance of CR2032type full-cell battery has alsobeen studied with the use of the self-prepared Li₃V₂（PO₄）₃/C as cathode, graphitecarbon and Li4Ti5O12as counter anode, respectively. The effect of different amountratios between cathode and anode on the electrochemical performance is alsoinvestigated.