Structure Control Of VO₂ Cathode And Its Zinc Storagr Performance

Aqueous Zinc Ion Batteries is considered as a candidate battery for large-scale energy storage and smart grid due to its unique advantages of high theoretical capacity,good safety,low price and environmental friendliness.However,the development of Aqueous Zinc Ion Batteries is restricted by key cathode materials.VO₂（B）usually has a stable tunnel structure,which allows the insertion and extration of Zn²⁺.However,the slow electrochemical reaction kinetics caused by the strong electrostatic interaction of Zn²⁺in VO₂crystals is an obstacle to improving the storage performance of Zn²⁺.In addition,the inherent poor conductivity of VO₂and the volume change caused by the phase transformation during the cycle seriously affect its cyclic stability.Therefore,in this paper,the structure of VO₂sample was regulated,and on the basis of synthesizing VO₂with the morphology of dandelion microspheres,oxygen vacancies were produced and PEDOT conductive polymer was coated,which was applied to the positive electrode of Aqueous Zinc Ion Batteries to improve the zinc storage performance of VO₂.The main contents are as follows:In the first aspect,VO₂samples with microsphere morphology composed of nanowires were synthesized by hydrothermal method.The morphology of the nanosphere alleviates the stacking problem of traditional nanowires,increases the specific surface area and improves the electrochemical performance.Through SEM and TEM characterization tests,the VO₂of nanowire formed microspheres was observed.The galvanostatic charge discharge test of Zn//VO₂battery shows that the capacity reaches 307 m Ah g^-1at 0.1 A g^-1current density.Compared with the literature,it is found that the morphology of microspheres has better zinc storage performance.In the second aspect,the generation of oxygen vacancies on VO₂samples through defect engineering can effectively alleviate the strong electrostatic interactions between Zn²⁺and lattice,and improve the electrochemical reaction kinetics.By SEM,TEM and EPR characterization testing,confirmed that the microspheres morphology of the sample and the oxygen vacancy formation.The b value and capacitance contribution were calculated to confirm the rapid reaction kinetics of VO_2-x.The higher discharge capacity of Zn//VO_2-xbattery was confirmed by the galvanostatic charge discharge test,which reached 377 m Ah g^-1at 0.1 A g^-1current density and 307 m Ah g^-1at 0.5 A g^-1current density.The ex-situ XRD test shows that the energy storage mechanism of Zn//VO_2-xbattery is the synergistic action of Zn²⁺insertion and chemical transformation.In the third aspect,the surface of the oxygen vacancy VO_2-xsample was coated with PEDOT conductive polymer,and the sample still maintained the morphology of dandelion like nanospheres.The coating of PEDOT conductive polymer improves the conductivity of the material,alleviates the structural collapse during the cycle,and improves the cycle stability of the battery.The morphology and composition of VO_2-x@PEDOT composites were investigated by SEM,TEM,FTIR and Raman.Galvanostatic charge discharge test confirmed that the cycling stability of the battery was improved by coating PEDOT,and the cycling stability of the battery was the best when PEDOT accounted for 5%of the total mass of the compound.The capacity reaches 392 m Ah g^-1at 0.1 A g^-1current density,and the capacity retention rate is 91.7%after 50 cycles.It shows excellent stability after 4200 cycles at 5 A g^-1current density The storage mechanism of Zn//VO_2-x@PEDOT battery was found to be the synergistic action of Zn²⁺insertion and chemical transformation by ex-situ XRD and ex-situ XPS tests.