Preparation And Electrochemical Properties Of Core-shell Vanadium Pentoxide Composites

Supercapacitors have the advantages of high power output,long cycle stability,maintenance-free,and wide operating temperature range,and they are an important part of the development of new energy storage systems.Vanadium material is an ideal candidate material for supercapacitor electrodes due to its advantages such as high theoretical specific capacity,abundant reserves,and low cost.However,the volume expansion during electrochemical reaction and the easy structural changes limit its application in electrode materials.Polyaniline(PANI)is a widely used conductive polymer material,it has been widely studied as supercapacitor electrode material due to its good conductivity,high theoretical specific capacity and processability,but the biggest disadvantage of polyaniline as an electrode material is poor cycle stability and structure collapse.Therefore,how to make use of the high specific capacity of the vanadium-based electrode material and the high specific capacity of the polyaniline electrode under high conductivity is an urgent need to pay attention to when designing and preparing new electrode materials for supercapacitor.The core-shell nanostructure has a promising application in electrochemical energy storage for supercapacitor electrode materials due to its volume effect and short ion transmission path during the electrochemical reaction.This thesis is based on the design and preparation of V2O5@polyaniline core-shell structure composite electrode material.By changing the content of polyaniline in V2O5@polyaniline core-shell structure composite electrode material,the structure,morphology and electrochemical property of the prepared V2O5@polyaniline core-shell nanostructure electrodes are systematically studied,and the vanadium-based electrode materials with high specific capacitance and good cycle stability for supercapacitors are developed,and the application of vanadium-based electrode materials in supercapacitor is widen.The thesis mainly includes introduction,the preparation of V2O5 nanowire and its electrochemical property research,the preparation of V2O5@PANI core-shell nanostructures and their electrochemical property research.The first part mainly describes the composition and development of supercapacitors,the research status and existing problems of V2O5 electrode materials,PANI electrode materials and V2O5 based composite electrodes.The research purpose,research contents,and the innovation points for this study are proposed.The second part mainly discusses the preparation,characterization and electrochemical property of V2O5 nanowires with uniform size and good dispersion.The third part mainly studies the preparation,characterization and electrochemical property of V2O5@PANI core-shell nanostructure electrodes with different polyaniline contents.Using the prepared V2O2@PANI as positive and negative electrodes to assemble symmetric supercapacitors,the electrochemical performance and cycle stability of the assembled devices are studied.The main research contents of the paper are as follows:(1)By using NH4VO3 as the vanadium source and by controlling the acid solution concentrations in HCl or HNO3 reaction systems,V2O5 nanowires with uniform size and good dispersion were prepared by hydrothermal treating in HCl or HNO3 reaction systems with different concentrations,and the effect of acid type,acid concentration and hydrothermal treatment time on the structure and morphology of V2O5 nanowires were systematically researched.The results showed that the optimal preparation condition of the V2O5 nanowires with uniform size and good dispersion was hydrothermal treatment at 85℃ for 16 h in 2 M HNO3 reaction system.The size of the prepared V2O5 nanowire is uniform,and its particle diameter is about 90-100 nm.In the three-electrode system,the electrochemical property of the prepared V2O5 nanowire electrode was tested by using 1 M Na2SO4 as electrolyte.It was found that the prepared V2O5 nanowire electrode had a low specific capacitance,poor cycle stability,and diffusion resistance and interface,and the mass specific capacitance was 85 F g-1 at a current density of 0.25 A g-1.(2)By using the prepared V2O5 nanowire with uniform size and good dispersibility as an oxidant and self-sacrificial template,aniline monomer was oxidized and polymerized on the surface of V2O5 nanowire,V2O5@PANI core-shell nanostructure electrodes were prepared material solution to form highly conductive.By controlling the mass ratio of V2O5 nanowire self-sacrificial template and aniline monomer,V2O5@PANI core-shell naostructure electrodes with different PANI contents were obtained,and the effect of PANI content on the structure,morphology and electrochemical property of the V2O5@PANI core-shell nanostructures were systematically investigated.The research results showed that the thickness of PANI loaded on the surface of V2O5 incraesed with the increase of the amount of aniline monomer in the reaction system,and its thickness gradually increased from 8.75 nm of V2O5@PANI-1 to 29.6 nm of V2O5@PANI-6.V,O,C,and N four elements were evenly distributed in the core-shell structure.By using a three electrode system,the electrochemical property of V2O5@PANI core-shell nanostructure electrodes with different PANI contents were tested in 1 M Na2SO4 electrolyte with a voltage range of-0.2～1.0 V.V2O5@PANI-3 core-shell nanostructure electrode showed good electrochemical property,its maximum mass specific capacitance was 238 F g-1.A symmetric supercapacitor V2O5@PANI-3//V2O5@PANI-3 was assembled by using V2O5@PANI-3 core-shell nanostructure material as positive and negative electrode in 1 M Na2SO4 electrolyte.After 5000 cycles,the capacitance retention rate of the assembed device was 89%.The core-shell structure not only improves the conductivity and the rapid capacity decay caused by the volume expansion effect of the V2O5-based electrode material,but also benefits the cycle stability of the polyaniline electrode during the electrochemical cycle.The research provides a new preparation method of vanadium-based selectrode materials with high specific capacitance and good cycle stability for upercapacitors,and also enriches the application of vanadium-based electrode materials.