Study On Interface Engineering Design And Modification Of Vanadium Based Oxide Cathode Materials In Aqueous Zinc Ion Batteries

With the rapid development of global economy,the increase in the rate of energy consumption,as well as the extraction and use of fossil energy leading to the emission of large amounts of greenhouse gases,causing serious damage to the environment.There is a huge demand for the development of new energy technologies in order to protect the environment and sustainable economic development,and the search for renewable energy sources and the development of green renewable energy storage technologies has become more urgent.There are various green energy storage methods,among which chemical batteries play an important role in the development of green energy storage.Lithium-ion batteries are widely used in portable electronic devices and electric vehicles due to their high energy density and long cycle life.However,the high cost of lithium-ion batteries due to the low natural abundance of lithium metal,as well as the use of conventional organic electrolytes that raise serious safety issues,have limited the use of lithium-ion batteries in large-scale energy storage devices.Aqueous multi-valent metal ion batteries hold numerous advantages and are considered as an alternative to lithium-ion batteries.The high natural reserves of elemental zinc,the unique physical and chemical properties of zinc metal,and the high safety of aqueous electrolytes have made aqueous zinc ion batteries（AZIBs）attractive to researchers among a wide range of aqueous batteries.However,compared to lithium-ion batteries,aqueous zinc ion batteries still have shortcomings in the development of cathode materials.The search for structurally stable,high-capacity cathode materials is the primary task to achieve their practical industrial application.The diversity of elemental vanadium valence states and the fact that vanadium oxides have a layered or tunneled structure and can provide high energy densities have been focused on as cathode materials for aqueous zinc ion batteries.This paper develops two aspects of work on the design of vanadium oxide modifications as well as electrochemical mechanism studies,the main work being as follows:1.Polyaniline molecules（PANI）were introduced as guest material to intercalate vanadium dioxide（VO₂）,and the effect of PANI molecules on the structural and electrochemical properties of the material was investigated on this basis.During the synthesis of the materials,two different structures of monoclinic phase PANI-VO₂ and layered L-PANI-VO₂ were obtained by adjusting the p H value of the solution.The results of scanning electron microscopy（SEM）and transmission electron microscopy（TEM）revealed that L-PANI-VO₂is a thin layered structure with lengths on the order of microns and thickness of 100-200 nm.X-ray photoelectron spectroscopy（XPS）and infrared spectroscopy（FTIR）tests demonstrated that polyaniline molecules were successfully inserted into VO₂,and the polyaniline molecules broadened the crystalline spacing of vanadium dioxide,extending the（001）planar layer spacing from 6.2?to 10.2?.Electrochemical tests have demonstrated the superior capacity,multiplicity and long cycle electrochemical performance of L-PANI-VO₂ The L-PANI-VO₂electrode has a specific capacity of 415 m Ah g^–1 at 0.1 A g^–1 current density and maintain 280m Ah g^–1 after 50 cycles,and 173 m Ah g^–1 after 1000 cycles at 2 A g^–1 current density.Ex situ X-ray diffraction（XRD）,scanning electron microscopy SEM and high reflection transmission electron microscopy（HRTEM）tests showed that the polyaniline molecules enlarged the crystalline spacing of vanadium dioxide,facilitating more zinc ions to（ex）-/intercalation from the cathode material.In addition,the flexible chain of conjugated polyaniline molecules can weaken the lattice stress caused by the（ex）-/intercalation process of zinc ions,improving the battery capacity and structural stability.In contrast,the content of polyaniline in PANI-VO₂ is relatively small,and X-ray structure diffraction demonstrates that the polyaniline molecules do not expand the material layer spacing,and the structure of the main PANI-VO₂ intrinsic monoclinic phase is maintained.Aqueous zinc ion batteries assembled with PANI-VO₂ and metallic zinc cathodes can reach a specific capacity of 350 m Ah g^–1 at 0.1 A g^–1 current density test.2.In order to improve the low capacity and poor cycle life of commercial vanadium oxide（V₂O₅）,we added vanadyl sulfate（VOSO₄·x H₂O）to 3 M Zn（CF₃SO₃）₂ electrolyte to improve the electrochemical performance of V₂O₅ in aqueous zinc ion batteries and to study its electrochemical mechanism.Electrochemical tests have shown that the maximum specific capacity of commercial V₂O₅ electrode can reach 570 m Ah g^–1 at 0.1 A g^–1 current density in3 M Zn（CF₃SO₃）₂+0.3 M VOSO₄·x H₂O electrolyte,and the capacity retention rate is more than 70%after 3500 cycles at 5A g^–1.In situ XRD,SEM and XPS were used to investigate the charging and discharging mechanism of the battery.It was found that there were a large amount of Zn₃（OH）₂V₂O₇·x H₂O byproducts occur on the surface of cathode material during the cycle process in Zn（CF₃SO₃）₂ electrolyte,leading to electrode capacity decay and poor cycling stability.In contrast,in the electrolyte with the addition of VOSO₄,Zn_xV₂O₅·n H₂O cyclically appears and disappears during the charging and discharging process,at the same time,the Zn₃（OH）₂V₂O₇·x H₂O byproducts are seriously inhibited,resulting in the reversible ex-/intercalation of Zn²⁺ions in the cathode material.The addition of vanadium oxide sulphate improves the cycling stability of the battery and is the fundamental reason for the excellent electrochemical performance of the electrodes.