Synthesis And Electrochemical Performance Of Vanadium Oxide Cathode Materials For Aqueous Zn-ion Battery

To solve the energy problem,we need to develop new energy and clean energy,and the research of new large-scale energy storage system（ESS）is the key to the transformation and utilization of clean energy.Traditional lithium-ion batteries（LIBs）are limited in the field of large-scale energy storage due to serious safety risks.The new energy storage system represented by water zinc-ion battery（AZIBs）has great potential in the application research of large-scale energy storage system,and can meet the increasing energy demand of people without causing pollution to the environment,so AZIBs has become the focus of researchers.Through continuous optimization of AZIBs,the energy crisis can be alleviated,environmental pollution can be reduced,and sustainable development can be achieved to ensure the sustainability of human survival and development.At present,an important factor limiting the application of AZIBs is the lack of high electrochemical activity and structurally stable cathode materials.Vanadium oxide is a kind of AZIBs positive electrode with great application potential,showing high specific capacity and stable cycle performance.However,vanadium oxides usually suffer from poor electrical conductivity,surface vanadium dissolution and other problems,so that their magnification and cycle performance are poor.Based on this,this paper studies the synthesis and electrochemical properties of V₂O₃ and V₂O₅vanadium oxides under different conditions,which are divided into the following tasks:（1）Composite of porous carbon materials with V₂O₃.First,the rod-like vanadium-based metal organic framework（V-MOF）precursors were prepared by organic ligand 1,4-naphthalenedicarboxylic acid and vanadium trichloride,and then the V-MOF was subjected to high-temperature heat treatment to obtain mesoporous V₂O₃/C composites.The prepared V₂O₃/C cathode material was found to have abundant pores,large specific surface area,and stable carbon skeleton structure by XRD,SEM,TEM,Raman,XPS,and BET tests.When used as AZIBs cathode,although the carbon content is close to 50%,the specific capacity of V₂O₃/C cathode can still reach 240m A h g^-1 at 0.5 A g^-1,and the capacity retention rate is 86.6%when the current density is increased from 0.5 A g^-1to 4.0 A g^-1,showing good rate performance.In addition,the specific capacity decayed only about 20%after 2000charge/discharge cycles at 10 A g^-1,which is better than that of commercial V₂O₃.Various test results showed that the hierarchical structure and carbon skeleton could effectively improve the structural stability and electrochemical performance of V₂O₃ in AZIBs.The present work provides some inspiration for the improvement of the electrochemical performance of V₂O₃.（2）Crystalline water was used as a modifier to improve the V₂O₅ crystal structure.First,V₂O₅ gels were prepared using commercial V₂O₅ and H₂O₂,followed by evaporation crystallization to prepare V₂O₅·x H₂O materials with a layered structure.A series of V₂O₅·x H₂O（HVO-0.5,HVO-1.0 and HVO-2.0）were prepared by adjusting the ultrasonic pretreatment time of V₂O₅ and H₂O₂.By adjusting the ultrasonic pretreatment time of V₂O₅ and H₂O₂,a series of HVO samples were prepared.The introduction of crystalline water in the HVO-1.0material and the optimization of the interlayer structure of V₂O₅ were demonstrated by XRD,SEM,TEM,XPS and TG tests.As the positive electrode for AZIBs,the HVO-1.0 electrode exhibited good rate performance(the specific capacity decreased from 264.07 m A h g^-1 to 189.71 m A h g^-1 when the current density increased from 0.5A g^-1 to 4 A g^-1,with a capacity retention rate of 71.8%)and excellent cycling stability(the first discharge specific capacity at a current density of 10 A g^-1 was 144.18 m A h g^-1 at a current density of 10 A g^-1 and 106.4 m A h g^-1after 8000 cycles with 73.8%capacity retention)and excellent cycling stability(first discharge specific capacity of 144.18 m A h g^-1 at a current density of 10 A g^-1 with 73.8%capacity retention),and better performance than that of commercial V₂O₅.This work provides an efficient and low-cost synthesis method for the practical application of V₂O₅ in AZIBs.（3）Polyaniline（PANI）was used as a modifier to composite with V₂O₅.Using a simple chemical oxidation polymerization method,PANI was polymerized in situ between the V-O layers of V₂O₅,and the V₂O₅@PANI composite with nano-flower-like structure was successfully prepared and the amount of aniline addition was optimized.Various electrochemical tests showed that the electrode obtained at 30μL of aniline（PVO-30）has high specific capacity(up to 398.5 m A h g^-1 at a current density of 0.5 A g^-1),good rate performance(83.98%capacity retention when the current intensity is increased from 0.5 A g^-1 to 4 A g^-1)and good cycling performance(,After200 charge/discharge cycles at 10 A g^-1,the specific capacity still maintains at 285 m A h g^-1,with a capacity retention rate of about 90%).The above results indicate that the composite of conducting polymer PANI and inorganic V₂O₅ can effectively compensate for their respective defects and improve the overall performance of the composite electrode.This work provides a new idea for the facile synthesis of V₂O₅@PANI inorganic-organic composite electrode materials.