Assembly And Performance Study Of All Solid-state Cable Type Copper Wire/graphene/manganese Dioxide Composite Fiber Supercapacitor

Supercapacitors?SCs?are a new kind of energy storage devices between conventional capacitors and secondary batteries,they have many advantages such as high power density,long life cycle,good reversibility and environmental friendliness,etc.With the rapid development of miniaturized portable electronic devices,energy storage devices with much larger volumetric energy densities are needed.In the series of supercapacitors,all solid-state flexible supercapacitor is given wide attention because it has not only light weight,high power density,long cycle life,excellent mechanical properties and safety performance,but also has good flexibility.Particularly,fiber-based solid-state flexible supercapacitor is expected in the portable electronics industry due to more tiny volume,high flexibility and easy wearability.Graphene is two-dimensional honeycomb lattice structure bonded by the close carbon atoms,this unique structure makes it show excellent mechanical,electrical,thermal and optical properties,and can be widely used in supercapacitors.Graphene fiber can be made from graphene and used as electrode material in fiber-type supercapacitor,this device generally exhibits a relatively low specific capacitance due to the lack of structural optimization and its low capacitance.Manganese oxide?MnO₂?is considered as one of the most promising supercapacitor electrode materials because of low cost,good electrochemical reactivity,environmental compatibility and high theoretical capacitance.Up to now,it is given more attention by researchs to develop MnO₂/graphene composite hybrid fiber electrode materials.However,MnO₂ electrode materials with rigidity has poor electrical conductivity although it possess high theoretical capacitance.If MnO₂ is incorporated into graphene fiber,the electrochemical property of the MnO₂/graphene composite hybrid fiber electrode materials will be improved while its flexibility and conductivity will be deteriorated.Therefore,how to improve the electrochemical property of the MnO₂/graphene composite hybrid fiber electrode materials and maintain good flexibility and conductivity at the same time is an urgent problem to develop MnO₂/graphene composite hybrid fiber electrode materials.In this thesis,flexible copper wire was used as substrate,and graphene suspension with high concentration was used as precursor.Cu wire/reduced graphene oxide/manganese dioxide?Cu/RGO/MnO₂?composite fiber electrode material with good flexibility,excellent electrochemical performance and high conductivity was prepared by using one-step dimensionally-confined hydrothermal method.The first chapter introduced the preparation,structure and properties of graphene fiber and manganese dioxide,and the characteristics of all solid-state flexible supercapacitor.Chapter 2 and Chapter 3 were the experimental parts consisted of the preparation and characterization of Cu/RGO/MnO₂ fiber electrode materials,the assembling all-solid-state flexible fiber supercapacitors and their capacitive property.Chapter 4 was the summary of the thesis.The main research contents were as follows:?1?Preparation and electrochemical property of Cu/RGO/MnO₂ fiber electrode material.a copper wire was used as the fiber-formed center and current collector,and it was placed into a glass capillary.Then graphene dispersion with high concentration used as precursor was injected into the glass capillary and it was heated at 230 ? for 2.5 h,Cu wire/reduced graphene oxide?Cu/RGO?composite fibers were prepared by an improved limited thermal gelation method.The Cu/RGO fibers were then followed by soaking in 6.0 mM KMn04 solution in a 150 mL flask.After stirring the reaction system for 5 min,it was refluxed at 70 ? for 120 min,the nanostructured ?-MnO₂ was successfully deposited on the surface of Cu/RGO fibers via in-situ reaction between carbon and KMnO4,and Cu/RGO/MnO₂?6.0?fiber electrode with high flexible was finally prepared after it was washed with deionized water and dried in the vacuum oven.By changing the concentrations of KMnO4 solution,Cu/RGO/MnO₂?M?fiber electrodes with different MnO₂ mass coating were obtained by the similar process,in which M was the concentration of KMnO4 solution.?2?Assembly and capacitance of flexible all-solid-state Cu/RGO/MnO₂ cable-type supercapacitors.By closely placing two Cu/RGO/MnO₂ fibers with parallel direction and using PVA-KOH gel electrolyte,highly flexible all-solid-state Cu/RGO/MnO₂ cable-type supercapacitors with good flexibility and enhanced capacitive performance were successfully assembled.The optimized all-solid-state Cu/RGO/MnO₂?6.0?fibers supercapacitor showed a high specific capacitance of 140 mF cm-2 at a current density of 0.1 mA cm-2,the enhanced capacitance retention of 97%after 500 bending cycles with a big angle of 120°,and relatively good stability?88%of initial capacitance values after 5000 cycles?.Moreover,it could light a LED lamp when it is connected with a battery aside from its excellent electrochemical performance,indicating that the assembled Cu/RGO/MnO₂ fiber supercapacitor could be used not only as an energy storage device,but also an electrical conduction cable,which has significant impact on the future energy storage applications.