Preparation Of Vanadium-based Cathode Materials For Aqueous Zinc Ion Batteries And Their Zinc Storage Performance

The rapid depletion of lithium resources has inspired researchers to investigate other electrochemical energy storage systems.Among them,research work on cathode materials for zinc ion batteries has focused on improving the energy efficiency,multiplier performance,power density and lifetime of zinc ion batteries.Vanadium oxide,as a layered structure material,has the advantages of low cost,abundant resources and high specific capacity,and is one of the most promising electrode materials for developing next-generation electrochemical energy storage.Among them,building nanomaterials to increase the active sites of electrochemical reactions and introducing crystal defects can both improve the capacity and multiplicative performance of vanadium-based anodes.In this thesis,hollow flower-like vanadium pentoxide nanomicrospheres were prepared by a solvothermal method.Vanadium tetrasulfide（VS₄）precursors were prepared using ammonium metavanadate and thioacetamide as raw materials and deionized water and ethylene glycol as solvents,and oxygen-defect-rich vanadium pentoxide（referred to as O_d-V₂O₅）was prepared by a one-step annealing method under oxygen atmosphere,on the basis of which V₅S₈/VO_xheterogeneous interfacial materials were prepared by annealing VS₄precursors under argon atmosphere,which exhibited an average discharge voltage of 0.79 V,which further improved the energy density of Zn-ion batteries.The details of the study are as follows.（1）Unique hollow flower-like V₂O₅nanomicrosphere materials were prepared by a template-free solvothermal method using commercial vanadium pentoxide（V₂O₅）as raw material,citric acid as reducing agent,diethyleneglycol and isopropanol as solvents.XRD,SEM and TEM results showed that HN-V₂O₅has a hollow lamellar nanostructure with a flower-like appearance microspheres.The HN-V₂O₅electrode exhibits high capacity of 415m Ah g^-1,excellent multiplicity performance(215 m Ah g^-1at 20 A g^-1)and cycling stability（81%capacity retention after 1000 cycles）when used as the cathode for Zn-ion batteries.The activation over process of the HN-V₂O₅electrode was also investigated.The results showed that during the activation process,the HN-V₂O₅electrode gradually changed from a biphasic reaction of Zn²⁺and V₂O₅to a solid solution-embedded monophasic reaction,and the rate of Zn²⁺deembedding was accelerated by the monophasic reaction after activation.（2）V₂O₅was prepared by annealing VS₄precursors under oxygen using a one-step annealing method and explored for different annealing temperatures X（X=100/200/300/400/500/600）Thecorrespondingsampleswerenamed（VS₄-100/VS₄-200/VS₄-300/VS₄-400/VS₄-500/VS₄-600）.The XRD,XPS,SEM-EDS,BET and electrochemical results showed that the VS₄precursor was converted to V₂O₅)only at annealing temperatures above 300°C,and the morphology changed from spherical to rod-like as the annealing temperature increased,and the BET results showed that VS₄-500 had the largest specific surface area(23 m²g^-1),the XPS results indicate that VS₄-500 contains oxygen defects,while the electrochemical performance of VS₄-500 is optimal(560 m Ah g^-1at0.1 A g^-1current density),and the depth of discharge is up to 95%based on the theoretical capacity of 589 m Ah g^-1of vanadium pentoxide.（3）The V₅S₈/V₂O₃heterogeneous interface material was prepared by annealing the VS₄ precursor under oxygen in one step,and the XRD and XPS results indicated that the lattice oxygen that must be contained in the VS₄precursor and the crystal structure of VS₄was retained as a sufficient condition for the formation of this heterogeneous interface.The anode from the V₅S₈/V₂O₃heterogeneous interface exhibits a unique electrochemical mechanism,which is transformed into a V₅S₈/VO_xheterogeneous electrode by an in situ electrochemical reaction,and subsequently exhibits a high capacity of 498 m Ah g^-1and a high energy density of 384 Wh Kg^-1with a high average discharge voltage（0.79 V）.The heterogeneous interface electrode improves the energy efficiency of the Zn-ion battery by 15%compared to that without the heterogeneous interface electrode.Meanwhile,the V₅S₈/VO_xhetero-interface electrode is able to exhibit a reversible capacity of up to 414 m Ah g^-1at 10 A g^-1,which exceeds the capacity record of most zinc ion batteries.