The Preparation And Performance Of Vanadium-based Cathode Materials In Aqueous Zinc-ion Batteries

In recent years,with the concern of energy crisis and environmental protection,some new energy sources such as solar energy,wind energy,geothermal energy or tidal energy,etc.,which are used to replace the traditional energy structure,have been developed and applied in large quantities.However,the efficient conversion and collection of new energy sources is still a major challenge and requires higher requirements for energy storage technology.Lithium-ion batteries（LIBs）have been widely used due to their high energy density,but the limited resources of lithium,high price and flammability and explosion have severely limited the further development of LIBs.Compared with LIBs,aqueous zinc ion batteries（AZIBs）have outstanding advantages in terms of low redox potential（-0.76 V vs.standard hydrogen electrode）,low cost,and great safety.Among the various types of AZIBs cathode materials that have been developed,vanadium-based materials are favored by researchers due to their rich valence variations and special framework structure,however,there are still problems such as easy collapse and dissolution of vanadium-based structures,poor electrochemical activity,poor environmental adaptability,and complicated preparation processes that limit the large-scale development of AZIBs.Therefore,in order to solve the above existing problems.Firstly,the vanadium oxides are optimized by Mn metal ion doping and the introduction of r GO conductive network to improve the capacity performance,rate performance,and cycling stability performance of the corresponding AZIBs devices,and the possible zinc storage mechanism and electrochemical reaction mechanism are explored in depth.Further,on the basis of the Mg metal ion doping modification,a gel electrolyte is introduced to match with it,which significantly broadens its practical application temperature range.In addition,vanadium-based cathode materials with Zn metal ions and structural water intercalation were prepared in large quantities by a simple preparation process,and the practical application value of AZIBs was verified by the assembly of high-loading and high-capacity devices.The specific research contents are as follows:（1）Mn VO@r GO cathode materials with both Mn metal ion doping and r GO conductive network composite were prepared by an efficient one-step hydrothermal reaction.By morphological and structural characterization,the Mn VO nanoribbons in Mn VO@r GO are wrapped by a large amount of r GO films,resulting in enhanced electrical conductivity.Further,the electrochemical performance tests show that the electrode has the outstanding advantages of high capacity,high rate and long cycle life,with a high discharge specific capacity of 360.3 m Ah g^-1 at a current density of 0.2 A g^-1and 88.9 m Ah g^-1 at a high current density of 20 A g^-1,and its capacity retention rate is close to 100%even after 10000 cycles.Finally,the practical application potential was verified by device assembly.（2）Firstly,the enhancement effect of Mg metal ion-doped vanadium dioxide on zinc ion migration was verified by theoretical calculations,and then Mg-VO₂（B）nanoribbon cathode materials were synthesized by a one-step hydrothermal preparation process,and the improvement effect of Mg doping on the capacity and rate performance of VO₂ was also demonstrated by electrochemical performance tests.Further,hydroxyethyl cellulose modified polyacrylamide（PAM-HEC）gel electrolyte was prepared to meet the requirements of the device in high and low temperature environments,and the DFT calculations demonstrated the confining effect of PAM-HEC on water molecules and its ability to effectively reduce the generation of interfacial by-products and promote the rapid diffusion transfer of Zn²⁺.Finally,the practical performance of the assembled AZIBs devices was verified under high and low temperature environments,which broadened the value of AZIBs for wide temperature domain use.（3）To solve the problem of complicated preparation process of vanadium-based materials,Zn VO·1.2H₂O cathode materials with Zn²⁺pre-embedded with structured water were synthesized in large quantities using a simple stirring preparation process.The uniform nanowire structure of Zn VO·1.2H₂O was characterized by morphological observation,which can effectively increase more specific surface area and improve the electrochemical activity.Electrochemical performance tests show Zn VO·1.2H₂O electrode has higher capacity performance and cycling stability compared to V₂O₅ Further,the zinc ion battery devices with high-loading and high-capacity were prepared by the large-area coating process and the cylinder cell assembly process by taking advantage of the large-volume preparation,and their value for large-scale business applications was verified by the cycling test and safety test.