Design And Performance Optimization Of Aqueous Zinc-ion Batteries Based On Vanadium-based Oxide Cathode

Aqueous zinc ion batteries,as a new type of rechargeable secondary battery,have received widespread attention for their high safety,low cost,and green advantages.However,the lack of suitable cathode materials is one of the main reasons hindering the commercial application of zinc ion batteries.Vanadium-based materials have received increasing attention due to their high theoretical capacity and abundant embedding sites.But the electrostatic interaction of divalent Zn ions with their host materials during charging and discharging and the poor electrical conductivity of vanadium-based materials lead to slow kinetics of Zn²⁺intercalation/extraction.In this thesis,alkali metal ion pre-embedded and carbon-coated V₂O₅ was designed to obtain high-performance Zn ion cathode materials as follows:（1）Vanadium oxide nanoribbons were prepared using different alkali metal ions（Li⁺,Na⁺,and K⁺）pre-embedded as cathode materials for zinc ion batteries.The effects of different alkali metal ions on the morphology,crystal structure,and electrochemical properties of the materials are investigated.The crystal structure of vanadium oxide was characterized using XRD tests.It is found that the crystal structure with the addition of KF and Li F exhibited a strong crystallinity.Electrochemical tests show that the addition of KF has the best electrochemical properties.Secondly,the effect of different ratios of potassium fluoride（KF）on the vanadium oxide is investigated.XRD tests show that the crystalline surface spacing of vanadium oxide decreases with increasing KF ratio,probably due to the replacement of some water molecules in the interlayer by metal ions.Finally,the mechanism of zinc storage in KF pre-embedded V₂O₅ is investigated.The parameters of electrochemical kinetics were obtained by calculating the CV curves at different scan rates,showing a capacitance-dominated zinc storage mechanism.The changes in the crystal structure of the cathode material during the charging and discharging process were tested by ex situ XRD and XPS.The results show that 0.75-KVO-300 has reversible Zn²⁺intercalation/extraction structures.The0.75-KVO-300 electrode was tested for cycling stability at a current density of 1 A g^-1.The first discharge capacity is 218 m Ah g^-1,and it retains 205 m Ah g^-1 after 50 cycles.It is demonstrated that the K⁺pre-embedded V₂O₅ provides a suitable channel for Zn²⁺intercalation/extraction to enable the assembled Zn-ion battery to exhibit excellent performance.（2）Carbon-coated and K⁺pre-embedded V₂O₅ nanoflowers（KVO-Cx）were prepared by hydrothermal and high-temperature annealing methods.The effect of different carbon contents on the microscopic morphology,crystal structure,and electrochemical properties of the products is carefully studied.It is demonstrated that the crystallinity of vanadium-based oxides is enhanced by increasing the added carbon source.The KVO-C3 cell assembled by Zn foil anode,KVO-C3 cathode,and 2 M Zn（CF₃SO₃）₂ electrolyte reaches a specific capacity of 389.2 m Ah g^-1 at a current density of 0.1 A g^-1.When the current density increases 50 times and returns to 0.1 A g^-1 after 140 cycles,the specific capacity remains at 83.5%of the initial capacity.KVO-C3 cell also exhibits good capacity retention of 90%and coulombic efficiency close to100%after 1000 cycles.It provides a high energy density of 209 Wh kg^-1 at a power density of 7000 W kg^-1.The carbon coating improves the electrical conductivity of the sample,while the unique nanoflower-like morphology and well crystallinity provide fast Zn²⁺kinetics.They contribute to improving the rate performance and cycling stability of the KVO-C3 cell.In summary,this thesis systematically investigates different alkali metal ions pre-embedded V₂O₅ to obtain K⁺-doped V₂O₅ nanoribbons with the best electrochemical performance.Subsequently,the morphology and crystal structure of K⁺pre-embedded V₂O₅ were improved by adding glucose as a carbon source to obtain a nanoflower-like microstructure.Thus,this thesis provides an effective strategy to improve the zinc ion storage properties of vanadium oxide cathode materials,laying the foundation for the large-scale application of zinc ion batteries.