The Research Of High-performance Vanadium-bsed Cathode Materials And Its Storage Mechanism For Aqueous Zinc Ion Batteries

Aqueous zinc ion batteries（AZIBs）have attracted wide attention in the field of energy storage due to its great advantages,including eco-friendliness,non-toxic and non-flammable electrolyte,low cost,abundant zinc metal,high theoretical capacity and low redox potential of zinc anode.The cathode materials are the part of key components of AZIBs,which determine the specific capacity and energy density of batteries to a large extent.Therefore,it is urgent to seek suitable cathode materials for the further development and application of AZIBs.Among many candidates,the vanadium-based materials have rised up to be the most promosing cathode due to its suitable channel for Zn²⁺diffusion and high therotical specific capacity.Moreover,vanadium oxides are the most stable among these vanadium-based materials.However,there are some inevitable problems of vanadium-based materials,including dissolution in electrolyte and low conductivity,which lead to an unsatisfactory electrochemical performance when they are applied as cathode materials of zinc ion batteries.According to the above problems,we have synthesized two kinds of vanadium oxides（VO₂·x H₂O and V₂O₃/CNT）and take them as cathodes for AZIBs,finally we comprehensively research their electrochemical performance and reveal their storage mechanism of Zn²⁺.The main works are as below:1.The VO₂·x H₂O nanobelt was synthesized by a facile one-step hydrothermal method and then used them as electrode of cathode in AZIBs with 2 M Zn（CF₃SO₃）₂electrolyte.The crystal water of VO₂·x H₂O nanobelts can act as an interlayer“pillar”and“lubrant”,effectively stabilizing the material structure and promoting the transmission,thus showing an extremely excellent cycling and rate performance.A reversible capacity of 376 m Ah g^-1was obtained in VO₂·x H₂O nanobelt electrode after 200 cycles at a current density of 1.0 A g^-1and an outstanding long-term cycling performance was presented at the current density of 15 A g^-1（no obvious specific capacity decay after 8000 cycles）,indicating an excellent reaction kinetics.Finally,we revealed the synergistic Zn²⁺/H⁺co-insertion mechanism of VO₂·x H₂O electrode by a series of in-situ XRD characterizations.2.A unique and with abundant oxygen vacancies composite cathode materials（V₂O₃/CNT）was synthesized by the in-situ compounding of V₂O₃and carbon nanotubes（CNT）in a hydrothermal and calcined methods.V₂O₃/CNT was used as cathode materials and 2 M Zn（CF₃SO₃）₂was used as electrolyte,assembled into coin cells.The function of carbon nanotubes not only can improve the conductivity of V₂O₃but also can effectively stabilize the host materials structure and shorten the diffusion route of Zn²⁺.Moreover,the abundant oxygen vacancies existed in V₂O₃/CNT can explore more active sites to effectively improve the efficiency of Zn₂₊storage.Therefore,V₂O₃/CNT electrode showed a superb electrochemical performance(243.2 m Ah g^-1at the current density of 0.5 A g^-1and211.6 m Ah g^-1at the current density of 5 A g^-1).Lastly,we also took a series of ex-situ characterizations to investigated systematically the structural and morphological evolution of V₂O₃/CNT electrode during cycling,the result indicating a synergic Zn²⁺/H⁺co-intercalation/de-intercalation mechanism.