Preparation Of Vanadium Oxide Based Cathod Material And Its Performance In Aqueous Zinc Ion Battery

Aqueous Zn-ion battery has become one of the most popular energy storage devices for its stable chemical properties,reliable aqueous electrolyte,low cost and easy assembly,large theoretical capacity and other advantages.Vanadium dioxide（VO₂）as a hot aqueous Zn-ion battery cathode material,with its low cost,variable valence state,easy preparation,especially the unique tunnel structure conducive to ion transmission and other advantages,has better prospects for industrial application.However,factors such as poor structural stability and relatively low conductivity limit the application of aqueous Zn//VO₂battery.In view of the problems existing in VO₂-based cathode materials,this paper mainly carried out the following three aspects of work:（1）VO₂was synthesized by hydrothermal method.On this basis,the VO₂electrode（K-VO₂-3:4）rich in oxygen vacancy was obtained by KOH activation.The results showed that KOH activation not only changed the morphology of VO₂,but also successfully introduced oxygen vacancy into VO₂.The increase of the specific surface area of VO₂after the activation of KOH provides more active sites for the electrochemical reaction,while the introduction of oxygen vacancy strongly promotes the diffusion kinetics of ions.Meanwhile,the energy storage mechanism of Zn//K-VO₂-3:4 AZIB is discussed by systematically analyzing the charging and discharging reaction process of K-VO₂-3:4.The K-VO₂-3:4cathode activated by KOH can reach A high capacity of 260.9 m A h g^-1when the current density is 0.2 A g^-1,which is higher than the untreated VO₂.After 3000 charge-discharge cycles at 5 A g^-1,a capacity retention rate of 88.1%was obtained.（2）The W⁶⁺doped VO₂was synthesized by one-step hydrothermal method.The VO₂doped with tungsten has the morphology of long strip with uniform size,and the lattice spacing becomes larger.The doping of W atom changes the morphology of VO₂,improves the slow diffusion kinetics of Zn²⁺,and improves the structural stability.The introduced W-O bond enhances the structural stability,and the pre-inserted W⁶⁺increases the lattice distance.In addition,when the current density is 0.2 A g^-1,the specific capacity of W-VO₂AZIB is340.2 m A h g^-1,and when the current density is 10 A g^-1,the capacity of W-VO₂AZIB can still maintain 76.5%after 2000 charge-discharge cycles,and the structural stability has also made great progress compared with that before doping W atom.The electrochemical kinetics of W-VO₂cathode was analyzed by Galvanostatic Intermittent Titration Technique（GITT）,and the Zn²⁺diffusion coefficient(D_Zn)of W-VO₂cathode was calculated.（3）The VO₂@CPAN composite electrode material（VO₂@CPAN）with three dimensional network structure of carbon fiber was prepared by combining electrospinning with simple hydrothermal method.The electrochemical properties of VO₂@CPAN and untreated VO₂were compared to explore the effect of composite carbon fiber on the performance of VO₂@CPAN AZIB.The three-dimensional mesh carbon fiber significantly improved the conductivity of VO₂cathode,alleviated the original agglomeration of VO₂,and increased the specific surface area of the VO₂cathode material in contact with the electrolyte.The VO₂@CPAN positive electrode can reach A high capacity of 191.3 m A h g^-1at a current density of 0.2 A g^-1,which is higher than the untreated VO₂.At the same time,an excellent capacity retention rate of 88.3%was obtained after 3000 charge-discharge cycles with the current density rising to 10 A g^-1.