Surface Modification And Zinc Storage Properties Of Vanadium Based Oxide Materials

Zinc ion batteries have the advantages of high theoretical volume specific capacity,abundant reserves and environmental friendliness,and are expected to replace lithium ion batteries in some areas with low battery volume requirements,so as to alleviate the problem of lithium resource shortage,and become a new generation of energy storage devices with great potential.However,the practical application of zinc ion battery technology still faces many challenges,especially the low capacity of cathode material,poor cycling stability and the damage of the battery caused by the growth of zinc dendrite,which have aroused extensive attention of researchers.The design of cathode materials for zinc ion batteries is one of the main factors of these problems.The cathode materials developed include manganese base materials,vanadium base materials,Prussian blue analogue and so on.As one of the main cathode materials of zinc ions,vanadium based material is expected to be used due to its advantages of high capacity and high ionic conductivity,but its practical application is still restricted by problems such as poor cyclic stability and vanadium material dissolution.In order to improve the energy storage characteristics of vanadium based materials and the cycle stability of batteries,vanadium based cathode materials were systematically studied by surface modification and interface engineering.The main research contents are summarized as follows:（1）An ion-intercalated layered vanadium oxide（NH₄）₂V₁₀O₂₅.8H₂O was synthesized by hydrothermal synthesis method,and its surface was modified by a simple low-temperature annealing process.In this way,the interlayer structure of the material is expanded and enhanced,while the surface structural stability of the material is greatly improved,and the cycling performance of the material under different current densities is enhanced.The capacity of 161 m Ah g^-1 is still maintained after 10000 times of discharging/charging cycle at 5 A g^-1 current density,and the capacity retention rate 62%.At the same time,400 m Ah g^-1 capacity is obtained under the current density of 0.5 A g^-1,and the energy storage performance is excellent.Through some physical and chemical characterization of the material,it is found that annealing treatment regulates the content of V⁴⁺and V⁵⁺in the surface of the mixed valence vanadium matrix material,and has a great influence on the properties of the material.This simple method of adjusting the ratio of vanadium in different valence states greatly improves the electrochemical behavior of materials and provides a new idea for the research of material modification.（2）Germanium ion was successfully embedded into the interlayer of layered vanadium oxide（NH₄）₂V₄O₉ by hydrothermal synthesis.The improved material layer spacing is greatly expanded,which is conducive to the insertion and release of zinc ions,and thus has a high capacity,with capacity of 485 m Ah g^-1 at the current density of 1 A g^-1.However,the material has the problem of rapid growth of zinc dendrites during the cycle,which greatly limits its practical application.Subsequently,the electrolyte was mixed with 10%polyethylene glycol additive,which greatly improved the cycling performance of the material.The assembled battery still maintains a capacity of 226 m Ah g^-1 after 2400 cycles of 5 A g^-1 current density,with no capacity decay and high cycle stability.The study shows that the method also isolates the cathode material from the electrolyte,inhibits the dissolution of the material in the electrolyte,and improves the stability of the material.At the same time,the method constructed a SEI film near the zinc negative electrode and induced zinc ions to deposit in the two-dimensional direction on the zinc negative electrode,which effectively solved the dendrite problem caused by the battery damage,and has a certain application prospect.