Preparation And Electrochemical Performance Of Vanadium-Based Cathode Material In Aqueous Zinc-Ion Battery

Aqueous zinc ion batteries（AZIBs）have attracted widespread attention as a new type of energy storage device due to their low cost and high safety.Among numerous electrode materials for aqueous zinc ion batteries,vanadium oxide posess good electrochemical performance in AZIBs due to its rich chemical valence states(V²⁺～V⁵⁺)and regular crystal structure,which have strong adaptability to zinc ions.However,semiconductor vanadium oxides are faced with slow dynamic process,poor conductivity weak structural stability in electrochemical process and serious volume effect,which still restrict their further application of vanadium oxides electrodes in AZIBs.Therefore,how to overcome the structural defects of vanadium oxide and improve its electrochemical performance has become an important issue for researchers.The main research contents of this thesis are as follows:1.By combining hydrothermal method with subsequent annealing treatment,C and N elements were doped into V₂O₃ to prepare V₂O₃/C electrode materials.The introduction of elements such as C and N not only effectively improves the conductivity of vanadium oxides,but also increases the transportation of Zn²⁺in V₂O₃/C.At the same time,the formation of oxygen defects was induced during the synthesis process.The presence of oxygen defects reduce the strong electrostatic interaction between Zn²⁺and oxygen elements in V-O,making it easier for Zn²⁺to（de）intercalate in V₂O₃ lattice,thereby accelerating the transport process of Zn²⁺.The composite material with a specific capacity of 407.0 mAh g^-1 at a current density of 0.10 A g^-1.After 500 cycles at current density of1.0 A g^-1,the specific capacity can still reach 357.0 mAh g^-1,with a capacity retention rate of 96.30%,demonstrating good cycling and rate performance.2.Using electrospinning method,vanadium microspheres with different internal structures（Solid sphere:VO_X-S,Core-shell sphere:VO_X-C,Hollow sphere:VOOH-H）were coated in polyacrylonitrile fibers,and then transformed into carbon fiber coated spherical V₂O₃（V₂O₃/CNFs）structures through high-temperature annealing.Using electrospinning method for carbon fiber coating,V₂O₃ microspheres are connected in series through carbon fibers,greatly enhancing the conductivity of V₂O₃,enabling rapid electron transfer on the carbon fibers,and the larger specific surface area shortens the diffusion path of Zn²⁺.In addition,we also used XPS,TG and other methods to demonstrate that the energy storage mechanism of V₂O₃/CNFs electrode is based on the co-（de）intercalation of water and Zn²⁺in the V₂O₃ lattice.The specific surface,active site and the zinc storage space of the electrodes are significantly different due to the different structures of V₂O₃ microspheres,which affects their electrochemical performance.Finally,different electrode materials with different structures were compared,and a carbon fiber coated hollow spherical V₂O₃ structure（V₂O₃/CNFs H）with a specific capacity of 260.0mAh g^-1 was achieved after 100 cycles at a current density of 0.1 A g^-1.At a current density of 1 A g^-1,after 500 cycles,the specific capacity still remains 236 mAh g^-1,with a capacity retention rate of 90.70%.3.By using a simple solvothermal synthesis strategy,VO_X/PBD/Ti₃C₂T_X organic-inorganic composite electrode materials based on Ti₃C₂T_X were obtained.As a new 2D material,Ti₃C₂T_X has high conductivity and large specific surface area,which effectively alleviates the shortcomings of poor conductivity and low ionic conductivity of VO_Xmaterial.At the same time,the introduction of poly（benzoquinone-diamine）（PBD）not only prevent the oxidation of Ti₃C₂T_X in the reaction process,but also provide better flexibility,ensuring the structural stability of VO_X/PBD/Ti₃C₂T_X electrode.Based on its stable structure and high conductivity,VO_X/PBD/Ti₃C₂T_X exhibits excellent electrochemical performance.After 200 cycles at 0.10 A g^-1,the specific capacity reached175.0 mAh g^-1.After 1000 cycles at 1.0 A g^-1,the specific capacity can still be maintained at 135.0 mAh g^-1,with a capacity retention rate of 73.0%,indicating that the construction of the organic-inorganic composite system significantly improves the electrochemical performance.