Preparation And Performance Of Vanadium Oxides For Aqueous Zinc Ion Batteries

Rechargeable lithium-ion batteries（LIBs）,with their advantages of excellent power density,high energy density and long service life,have been widely used in portable electronic products.However,limited lithium resources,high cost,and the use of organic combustible electrolytes severely limit the application of large-scale lithium-ion batteries,therefore,it is necessary to explore new energy storage systems to replace LIBs.Aqueous zinc-ion batteries（AZIBs）have rapidly developed as a competitive and promising alternative due to their low cost,high safety,abundant zinc resources,high theoretical capacity(820 mAh g^-1)and low redox potential（-0.76V vs SHE）.So far,the cathode materials used for AZIBs mainly include manganese oxide,vanadium oxide and Prussian blue analogues,among which vanadium oxide has attracted wide attention due to its various valence（+2～+5）,suitable layered structure and high theoretical capacity.However,vanadium oxides still have some inherent limitations,such as unsatisfactory electrical conductivity and slow kinetics due to strong electrostatic interaction with Zn²⁺,showing poor cyclic stability,which hinder their further application in AZIBs.In this paper,aiming at low electrical conductivity,structural instability and other problems existing in vanadium oxide cathode,we take some strategies such as the introduction of defect,composite with conductive polymer or carbon materials,and ion intercalation,expecting to improve the conductivity of the materials,enhance the transmission dynamics and structural stability of the material during charging/discharging.Specific research contents and results are as follows:1.Oxygen-rich defective V₂O₃/poly(3,4-ethylenedioxythiophene（PEDOT）（V₂O₃-O_d@PEDOT）composites by the sulfur-assisted thermal reduction and the following in-situ polymerization method.In this preparation process,the sulfur powder was used as a reducing agent to reduce the part of V⁵⁺to V²⁺and the mixed valence state of V³⁺/V²⁺is beneficial to improving ionic conductivity,while leading to the formation of a large number of oxygen defects.The existence of oxygen defects can weaken the electrostatic interaction between Zn²⁺and the host material,facilitating rapid Zn²⁺intercalation/deintercalation.The successful coating of conductive polymer PEDOT can enhance the conductivity of the material,effectively buffer the volume expansion caused by repeated intercalation/deintercalation of Zn²⁺and avoid structural damage,which is conducive to the long-term cycle stability of the electrode material.V₂O₃-O_d@PEDOT used as the cathode material of AZIBs.it shows high reversible capacity of 495 mAh g^-1 at current density of 0.1 A g^-1,excellent rate performance(the capacity is 189 mAh g^-1 at 8.0 A g^-1).and good long cycle stability that the capacity retention rate is 90.1%after 1000 cycles at8.0 A g^-1,meanwhile,kinetic characterization further proved that the V₂O₃-O_d@PEDOT electrode has higher diffusion coefficient of Zn²⁺.Therefore,V₂O₃-O_d@PEDOT is expected to be a potential positive electrode material for AZIBs.2.Using the solvothermal method to grow V₂O₃ nanosheets on carbon cloth（V₂O₃@CC）,the use of flexible substrate carbon cloth can effectively avoid the accumulation of V₂O₃ nanosheets.The porous structure of three-dimensional（3D）interconnecting nanostructures can effectively promote ion transport,alleviate the volume change in the process of charge/discharge,and facilitate the full contact of electrode materials and electrolyte,as well as provide more active sites.Carbon cloth has high electrical conductivity,which can effectively improve the electrochemical performance of the material when combined with V₂O₃.Carbon fiber with 3D interconnect structure can provide larger active surface,large number of exposed active centers and efficient mass transfer process,so as to promote the reaction kinetics and obtain excellent rate performance and cycle performance.At the same time,a layer of nano-zirconium dioxide（ZrO₂-Zn）was coated on the surface of zinc sheet to induce homogeneous deposition of Zn²⁺,slow down the formation and growth of zinc dendrites.V₂O₃@CC and ZrO₂-Zn respectively used as cathode and anode electrodes for zinc ion batteries,which shows high specific capacity of 552 mAh g^-1 at 0.1 A g^-1 current density,and at 5.0 A g^-1 current density the capacity retention rate is 83.6%after 2500 cycles.3.Zinc ion intercalated V₂O₅ nanosheets with crystalline water,Zn_xV₂O₅·nH₂O（ZnVOH@CC）were grown on carbon cloth with flexible substrate by a one-step hydrothermal method.The pre-inserted Zn²⁺and crystal water act as the interlayer"pillar",which increases the layer spacing of V₂O₅,weakens the electrostatic interaction between ions and host lattice,and improves the ion transport dynamics during charge/discharge.ZnVOH nanosheets form porous three-dimensional structure,effectively shortening the transport path of Zn²⁺and buffering the volume changes caused by ion intercalation/deintercalation,the porous structure of carbon cloth and ZnVOH facilitates the penetration of electrolyte,increases the contact area between electrolyte and material,and enhances the structural stability of the material.Benefiting from the above advantages,ZnVOH@CC used as the cathode material of AZIBs shows high specific capacity of464.9 mAh g^-1 at 0.1 A g^-1,and still has a capacity of 208.1 mAh g^-1 after 1000 cycles at1.0 A g^-1（98%retention）.Even after 10000 cycles at 5.0 A g^-1 high current density,it also shows good cycle stability,nearly 100%coulomb efficiency.In addition,matching ZnVOH@CC and Cu₂Se,assembled ZnVOH@CC//Cu₂Se full cell also shows higher reversible capacity and good cycle stability.