Study On Preparation And Electrochemical Properties Of Modified Vanadium Oxide Composites

In recent years,with the increasing demand for energy,aqueous zinc ion batteries(AZIBs)have attracted wide attention.It has many advantages over lithium-ion batteries,such as higher safety,lower cost and more environmentally friendly.Vanadium-based compounds,especially vanadium oxides,have been developed for many years as the positive electrode of AZIBs.Due to its rich vanadium valence,deformable V-O polyhedral and adjustable chemical composition,it has a fast ion diffusion rate and good reversible capacity,which provides a great opportunity for the development of emerging energy storage technology.However,there are also some practical problems,such as vanadium oxide in the water system electrolyte is easy to dissolve,the structure is unstable,resulting in poor cycle stability and other problems.Doping modification strategy is another effective way to improve the electrochemical performance of AZIBs and prevent the structural collapse of vanadium oxide materials.Therefore,several vanadium cathode materials were summarized and modified in this paper:(1)Inspired by the doping strategy of metal ions,the storage kinetics of zinc ions can be synergically promoted by embedding a conductive polymer with a conjugated structure into the layered vanadium pentoxide due to the electron coupling effect at the molecular level.This is because on the one hand,electron transfer of conjugated conductive polymer to the lattice frame of vanadium oxide can reduce the valence state of vanadium and essentially improve the conductivity of vanadium.On the other hand,the insertion of large size conjugated conductive polymer can further expand the crystal interface distance,resulting in rapid diffusion of zinc ions.Poly3,4-ethylene dioxythiophene(PEDOT)has good stability,easy synthesis,low oxidation potential,and can be used as a kind of intercalating agent.It is a very popular conductive polymer in recent years.Due to its excellent rate performance and conductivity,as well as the strong synergistic;it is expected to improve the electrochemical performance of materials.Therefore,we prepared PEDOT-V₂O₅composite material.The reversible capacity of PEDOT-V₂O₅ material reached 325 m A h g^-1 when the current density was 50 m A g^-1,and the capacity retention rate was 92.3%after 100cycles.Therefore,the PEDOT-V₂O₅ composite prepared by this strategy can solve the structural collapse problem of V₂O₅ in the water system Zn SO₄ electrolyte,and improve the electrical conductivity and structural stability of the material.The V₂O₅ material is also modified by the doping method of metal ion Na⁺,and the controllable amount of Na⁺is inserted into the V₂O₅ layer to form a stable Na-O bond between the V₂O₅ layers,so as to prevent the collapse of V₂O₅ structure and the dissolution of the V₂O₅ in the electrolyte.Na-V₂O₅ material is prepared by simple hydrothermal method.By alternating current impedance test and analysis,the embedding of Na⁺greatly improve the electrical conductivity of the material,and it is concluded that the material has the high irreversible capacity and capacity retention through constant current charging and discharging test results,this result is due to the Na⁺doped inhibits material structure collapse and dissolved in the electrolyte,cyclic voltammetry test results also proved this conclusion.Therefore,the strategy of doping V₂O₅ with metal ion Na⁺has proved feasible.Not only the electrical conductivity of the material has been improved,but also the structure of the material is more stable and the performance has been improved.The reversible capacity of Na-V₂O₅ material reached 330 m A h g^-1 when the current density was 50 m A g^-1.In addition,this result provides a potential strategy for improving the electrochemical stability of V₂O₅.(2)Because the application of V₂O₃ material in AZIBs is still relatively few,with fluorinated organic zinc trifluoromethane sulfonate solution as the electrolyte,and the price of raw material V-MOF is expensive,not suitable for large-scale commercial applications.Although V₂O₃@C porous material positive electrode has a more objective specific capacity,V₂O₃ and other vanadium-based compounds,has the same shortcomings,especially the structure of the material is easy to collapse,and because of the environmental friendly demand,we need to use Zn SO₄ as the electrolyte.Therefore,the glucose carbon spheres doped with V₂O₃(V₂O₃/C)nanocomposites were prepared by using environmentally friendly,non-polluting,non-toxic and harmless glucose carbon spheres as the template and relatively cheap vanadium acetylacetone oxy as the vanadium source.When the current density is 50m A g^-1,the initial reversible capacity of V₂O₃/C composites is 150 m A h g^-1,and the capacity retention rate is 66.7%,which is only 23.1%compared with that of pure phase V₂O₃ composites.Moreover,it is proved that V₂O₃/C composites have a more stable structure through the ratio performance test.The feasibility of our strategy is supported by the fact that carbon-based materials are simple to produce because they are cheap,plentiful,readily available,environmentally friendly,rapidly regenerative,and have a good inhibition effect on structural collapse.(3)Metal ion doping is an effective way to improve the electrochemical performance of AZIBs vanadium cathode and prevent the material structure from collapsing.First of all,through a simple hydrothermal method of preparing Mg²⁺doped VO₂ and used as the cathode material of AZIBs,introducing our Mg²⁺the layered structure of VO₂,thanks to the Mg²⁺doping in the VO₂ lattice,the introduction of the defects and provides structural support,and improves the ion migration rate,compared to the pure material,material structure more after doping Plus stability,so it shows higher reversible capacity and capacity retention,as well as excellent magnification performance.