Research On The Assembly And Performance Of All Solid-state Vanadium Pentoxide-based Fiber Capacitors

In recent years,flexible supercapacitors have become promising energy storage devices;they can be extensively used in various electronic devices such as portable,stretchable,wearable,compressible electric devices.But the traditional supercapacitors are still insufficient in its flexibility,comfort and wearability,making fiber supercapacitors be given wide attention.The fiber-shaped supercapacitors not only possess good capacitance,but also present excellent flexibility,light weight,good bendability and can be easily integrated into multifunctional electronic devices.Although flexible fiber-based supercapacitors have been researched extensively,there still is a great challenge that how to improve their energy density without sacrificing their cycle life and power density.Vanadium pentoxide(V2O5)has been used as electrode materials for supercapacitors due to its high theoretical capacitance,but its potential application is limited due to its poor flexibility and low conductivity,especially for V2O5-based fiber supercapacitors.Therefore,how to improve the flexibility and conductivity of V2O5-based fiber supercapacitors with high capacity is the key to solving large-scale applications.In this thesis,the electrochemical and mechanical properties of V2O5 fiber electrode have been improved by adding single-walled carbon nanotubes(SWCNTs)with high conductivity and mechanical properties into V2O5 fiber electrode.The thesis includes five chapters.The first chapter focuses on the structure,preparation,application,the research status,and the challenge of the fiber electrodes and fiber supercapacitors,carbon nanotube(CNT)fibers,V2O5-based flexible electrodes and flexible V2O5/SWCNT flexible hybrid materals;Chapter 2 to 4 are experimental parts and result discussion,including the preparation of V2O5 fibers,V2O5/SWCNT hybrid fibers and SWCNT/reduced graphene oxide(RGO)hybrid fibers,the assembly and characterization of V2O5/SWCNT based symmetric and asymmetrical fiber supercapacitors;Chapter 5 is the summary of the whole thesis.The main research contents are as follows:(1)The preparation and electrochemical property of V2O5 fibers electrode.The V2O5 nanobelt dispersion was prepared by hydrothermal method,and then V2O5 fiber electrodes were prepared by a wet-spinning technology.In there-electrode test system,the electrochemical property of the as-prepared V2O5 fiber electrodes was charactezied,its volumetric capacitance was only 5 F cm-3 in 1 mol L-1 Na2SO4 electrolyte.In addition,the mechanical property of the fiber electrode was also tested.(2)All-soild-state V2O5/SWCNT-based symmetric fiber supercapacitors.V2O5 nanobelts and SWCNT was used as assembled units,V2O5/SYWCNT hybrid fibers with different SWCNT contents were prepared by a wet-spinning technology.When the amount of SWCNT was 10%,the hybrid fiber electrode had the highest volumetric capacitance(99 F cm-3).By using PVA-H3PO4 as a gel electrolyte,an all-solid-state V2O5/SWCNT//V2O5/SWCNT symmetric fiber supercapacitor was assembled by using V2O5/S WCNT-10 hybrid fibers as positive and negative electrode.The V2O5/SWCNT//V2O5/SWCNT fiber supercapacitor exhibited good capacitance,excellent cycle stability and flexibility.(3)All-soild-state V2O5/SWCNT//SWCNT/RGO asymmetric fiber supercapacitors.By using SWCNT and RGO as assembleing units,SWCNT/RGO hybrid fibers were also prepared by using the wet-spinning method.To further increase the energy density of the fiber supercapacitor,all-soild-state asymmetric fiber supercapacitors V2O5/SWCNT//SWCNT/RGO was assembled by using V2O5/SWCNT hybrid fiber as positive electrode,SWCNT/RGO hybrid fiber electrode as negative electrode,and the PVA-H3PO4 as the gel electrolyte.The two-electrode electrochemical test results show that the device not only possesses good electrochemical performance,but also shows good mechanical property.The voltage window of the asymmetric fiber supercapacitor could be expanded to 1.5 V,and its maximum volume energy density could be reached 1.95 mWh cm-3.In addition,the electrochemical properties of the device did not change obviously after bending with various angles and repeated bends,indicating that the device had outstanding flexibility.Therefore,the introduction of the suitable amounts of SWCNT into the V2O5 fiber electrode could enhance its electrochemical properties and flexibility,and assembling an all-solid-state asymmetric fiber supercapacitor was an effective way to increase energy density of fiber supercapacitor.