Research On The Preparation And Raman Spectroscopy Of Vanadium-based Cathode Materials For Aqueous Zinc-ion Batteries

Among many energy storage equipments,aqueous zinc-ion batteries（AZIBs）have attracted much attention because of their high safety and low cost.However,the strong electrostatic interaction between divalent Zn²⁺and the crystal structure of the cathode materials results in slow diffusion kinetics.Therefore,the development of high-performance cathode materials is the key to realize AZIBs with high energy density and long cycle life.Vanadium oxides have attracted extensive attention due to their high theoretical capacity（multi-electron transfer properties）and open framework.However,the low electrical conductivity of vanadium oxides,the dissolution of vanadium in aqueous electrolytes and the structural damage caused by the repeated intercalation/extraction of Zn²⁺,leading to low energy density and poor electrochemical performance of AZIBs.In addition,the energy storage mechanism for vanadium oxides is unintelligibility and controversial.Herein,V₂O₅ is taken as the research object to fabricate the vanadium oxides composites with high energy density and long cycle life through the combination strategies of guest pre-intercalation and composite with high conductive carbon materials.Furthermore,the enhanced zinc storage mechanism is studied by a variety of in-situ and ex-situ characterization techniques.The main results are as follows:（1）Orthorhombic V₂O₅ nanobelts is prepared by hydrothermal and heat treatment processes.When it is used as a cathode for AZIBs,V₂O₅ nanobelts exhibit excellent zinc storage capacity:large capacity of 380 m Ah g^-1 at 0.2 A g^-1 and high capacity retention rate of 95%after 1000 cycles at the current density of 5 A g^-1.The V₂O₅nanobelts cathode exhibits a Zn²⁺/H⁺insertion/extraction storage mechanism during charge/discharge processes by in-situ Raman spectroscopy investigations.（2）A composite composed of PEDOT-intercalated V₂O₅ nanosheets and expanded graphite（V₂O₅/PEDOT（?）EG）is fabricacted via high-energy ball milling method.Using PEDOT intercalation to modify the crystal structure can increase the layer spacing of V₂O₅ and stabilize its crystal structure,while composite with expanded graphite can enhance the conductivity of V₂O₅.When it is used as a cathode for AZIBs,the V₂O₅/PEDOT（?）EG composite exhibits excellent zinc storage capacity with large capacity of 580 m Ah g^-1 at 0.2 A g^-1 and high capacity retention rate of 99%after 500cycles at the current density of 10 A g^-1.The V₂O₅/PEDOT（?）EG composite cathode exhibits a Zn²⁺insertion/extraction storage mechanism during charge/discharge processes by in-situ Raman spectroscopy investigations.