Research On The Preparation And Modification Of Vanadium Oxide（V₂O₅ And VO₂） For Zn²⁺ Storage

Vanadium-based oxides are widely used as electrode materials in various battery systems due to the multivalent state of vanadium element that can undergo redox reactions,and its layered structure is conducive to the free insertion/extraction of charge ions.According to existing research,V_xO_y as an electrode material shows excellent metal ion storage performance.However,the multivalent metal ion will have a strong electrostatic force between the host material during the extraction/intercalation process,which will cause the destruction of the crystal structure,and then affect the cycle stability of the battery;in addition,the inorganic compound is not conductive well as an electrode material.The characteristics of poor performance and the dissolution of materials in the cycle process will affect the overall performance of the battery.As we all know,the structure of the material will play a decisive role in the performance of the material.Therefore,adjusting the crystal structure of the cathode material through an appropriate method may greatly improve the zinc storage performance of the material from the perspective of optimizing the crystal structure.In this article,we choose V₂O₅and VO₂（B）as the research objects to conduct the following two researches:（1）K_0.23V₂O₅（KVO）was prepared by hydrothermal synthesis,and the effect of pre-inserted K⁺on the electrochemical performance of V₂O₅ was explored.Characterization by XRD,XPS,Raman,SEM,TEM,etc.showed that the prepared K_0.23V₂O₅ has a higher purity.When using two vanadium-based materials of pure V₂O₅and K_0.23V₂O₅,as cathode materials for zinc storage,compared with pure V₂O₅,K_0.23V₂O₅ has better electrochemical performance.Reversible capacity of 250 m A h g^-1at the current density of 0.1A g^-1 and excellent long-term cycle stability(2.0 A g^-1)with a capacity retention rate of 92.8%(103 m A h g^-1)after 500 cycles were achieved.After kinetic calculation and analysis,KVO has a faster ion diffusion rate(1.88×10^-9～2.6×10^-8 cm² S^-1)and a smaller electrochemical impedance.Finally,this article applied ex-situ XRD,XPS,Raman,and TEM to prove that KVO mainly stores zinc ions in the form of intercalation/extraction during charging/discharging process.（2）The VO_2-x with oxygen defects was prepared by simple hydrothermal synthesis and solution reaction methods（Na BH₄ as reducing agent）.And XRD,Raman,TEM,PALS,UV-vis DRS and EPR were used to prove the existence of oxygen defects.The electrochemical performance testing results revealed that the Zn//VO_2-x（B）battery can stably cycle for 40 cycles at a current density of 0.1 A g^-1,while Zn//VO₂（B）battery shows a sharply decreased specific capacity;The former still has a reversible capacity of nearly 150 m A h g^-1 after 700 cycles even at a current density of 3.0 A g^-1,while the latter still exhibits a sharply decreased specific capacity.In terms of reaction kinetics,the Zn//VO_2-x（B）battery has a higher ratio of pseudocapacitance behavior(1.0 m V s^-1;92.7%),smaller electrochemical impedance and faster zinc ion diffusion coefficient.In addition,compared with Zn//VO₂（B）batteries,Zn//VO_2-x（B）batteries exhibit significantly improved energy density and power density.Based on the consideration of excellent zinc storage performance of VO_2-x（B）,the electrochemical performance of high-loading VO_2-x（B）electrode also was explored.Specifically,it retained nearly specific capacity of 250 m A h g^-1 after 50 cycles at a current density of 0.1 A g^-1.Finally,an insertion/extraction mechanism of Zn//VO_2-x（B）battery during charging and discharging was demonstrated by ex-situ XRD,XPS,TEM-Mapping and other characterization technique.