Construction And Research Of High Performance Aqueous Vanadium-Based Zinc Ion Batteries

The issues including energy crisis,greenhouse effect and air pollution have promoted the development of new energy storage systems.Among them,lithium-ion batteries（LIBs）are already widely used in consumer electronics and（hybrid）electric vehicles because of their high energy density.However,problems such as scarce lithium resources,complex manufacturing process and toxic/combustible organic electrolytes hinder the large-scale application of LIBs.Recently,rechargeable aqueous zinc-ion batteries（AZIBs）are seemed as the most competitive candidates for next generation energy storage system due to their inherent safety,low cost,high energy density and natural abundant zinc resources.Among many kinds of AZIBs,vanadium-based zinc ion batteries have been widely concerned for their superior energy storage capacity and stability.As a typical cathode material,vanadium oxide has the characteristics of variable structure,abundant valence states,low cost and high theoretical capacity.However,low conductivity,collapse of structure and dissolution of vanadium in the cycle process restrict the further development of vanadium-zinc batteries.On the other hand,as another important component of zinc-vanadium battery,the negative electrode still has serious problems of dendrite growth and by-products formation during repeated zinc plating/stripping.The uneven growth of zinc dendrites will puncture the separator and cause internal short circuit.Therefore,it is necessary to develop cathode materials with high capacity and long cycle stability to construct high performance zinc ion battery.Additionally,problems in anode should also be concerned that including dendrite growth,by-products and zinc corrosion etc.In view of the above problems,in order to comprehensively and systematically improve the electrochemical performance of vanadium based AZIBs,vanadium oxide cathode materials and zinc metal anode are investigated in this thesis,respectively.In terms of positive electrode construction,based on defect engineering and structural construction,we have designed oxygen involved vanadium oxide and graphene-like structure of ultra-thin vanadium oxide.The fabrication methods are easy to operate and the performance is superior.Electrolyte additive is one of the effective strategies for improving zinc anode.We have developed two different electrolyte additives which can efficiently inhibite the production of zinc dendrites and by-products.In addition,the energy storage mechanism of vanadium oxide anode material and the uniform deposition mechanism of zinc induced by additives in electrolyte were also studied and analyzed in this thesis,which provides a reference for the research of the mechanism of vanadium based ZIBs.According to the above illustration,the following research results are obtained:（1）Oxygen vacancies of commercial V₂O₅ induced by mechanical force for aqueous zinc battery.The practical application of future water zinc-ion batteries requires low-cost,simple and efficient manufacturing methods.Herein,commercial V₂O₅ cathodes with oxygen vacancies were fabricated through a simple mechanical ball milling method.Electrochemical characterization and DFT theoretical calculations suggest that mechanical force can directly induce the oxygen vacancies in commercial V₂O₅,which significantly enhance the diffusion of Zn ions.Benefiting from the excellent electrochemical properties,O_V-V₂O₅ shows higher capacity,better magnification performance and better cycling stability than commercial V₂O₅.The capacity of the O_V-V₂O₅//Zn battery can remain 85.2%after 2500 cycles.（2）Vanadium oxide by atomically thin graphene-analogous V₂O₅·n H₂O for aqueous zinc battery.Achieving super-high capacity of cathode materials is a vital way to realize high practical energy density in aqueous vanad-based zinc batteries,which however remains a huge challenge.Herein,Based on density functional theory（DFT）calculations,we predict the ultra-high capacity of single-layer vanadium oxide.In experiment,we prepared graphene-analogous V₂O₅·n H₂O（GAVOH）with a thickness of about three atomic layers,which achieve ultra-high capacity of 714 mAh g^-1.Electrochemical research shows that pseudocapacitive effect is unveiled to mainly contribute to the super-high capacity due to the highly exposed GAVOH external surface.In situ Raman and synchrotron X-ray techniques unambiguously uncover the Zn²⁺ion storage mechanism.Carbon nanotubes（CNTs）are further introduced to design GAVOH-CNTs gel ink for large-scale cathode fabrication.The hybrid cathode demonstrates ultra-stable cycling and excellent rate capability and delivers a high energy density of 476 Wh kg^-1 at 76 W kg^-1;228 Wh kg^-1 is still retained at high mass loading of 10.2 mg cm^-2.（3）Inhibition of zinc dendrites by chromium ion electrolyte additive.Zinc deposition induced by additive is one of the effective strategies to solve the zinc metal negative electrode problem of vanadium-based zinc ion batteries.Herein,we designed a low-concentration chromium sulfate additive and zinc sulfate mixed electrolyte which can construct in situ zincophilic sites.The electrolyte has the characteristics of non-flammability,simple preparation and low cost.The negative electrode performance results showed that the mixed electrolyte guaranteed excellent cycle stability and high reversibility and high coulomb efficiency.XPS and synchrotron X-ray techniques have proved that Cr₂O_3-x molecular clusters are formed after Cr and Zn ions are deposited on zinc surface during zinc plating/stripping.The theoretical calculation of DFT reflects that Cr₂O_3-x molecular clusters have higher adsorption energy for zinc,and a large number of negative charges gather around the clusters,which can induce the uniform deposition of zinc atoms,thus inhibiting the growth of dendrites and the generation of by-products.The electrochemical test results show that the V₂O₅//Zn battery with chromium sulfate has better cycling and stability than the battery with pure zinc sulfate electrolyte.（4）Inhibition of zinc dendrites by carbon quantum dots electrolyte additive.The poor reversibility of zinc metal anode has hindered the practical application of water-based zinc ion batteries,which is mainly related to dendrite growth and side reactions.Herein,the Zn SO₄+CQDs mixed electrolyte was designed by introducing carbon quantum dots（CQDs）with the size of about 3-5 nm into the original location of zinc sulfate solution by a simple hydrothermal method.CQDs can control the nucleation process and promote uniform deposition of zinc,thus inhibiting the production of zinc dendrites and by-products.The electrochemical tests of Zn anode show that the Coulomb efficiency of the symmetrical cell with CQDs electrolyte is significantly improved compared with the pure zinc sulfate electrolyte.The symmetric battery with CQDs was able to obtain a cycle life of 1500 h at the current density of 1 mA cm^-2 and capacity of 1 mAh cm^-2.The V₂O₅//Zn cells assembled with Zn SO₄+CQDs electrolyte also exhibit excellent electrochemical performance.