| Fibrous supercapacitors not only have the advantages of fast charge and discharge rate,high power density,long service life,etc.,but also can meet the requirements of miniaturization,integration,flexibility and wearability,it is one of the priority development directions for high energy density flexible energy storage devices.However,the current fiber capacitors have defects such as difficulty in optimizing the balance of specific capacitance and flexibility and narrow operating temperature window,which severely restrict their application development.Therefore,without sacrificing volumetric power density,cycle life and other performance parameters,exploring the optimal balance between the flexibility of fiber electrode materials and electrochemical performance is an effective means to solve the bottleneck problem.The Ti3C2T,(MXene)with two-dimensional layered structure has a metal-like conductivity of 15000 S cm-1 and a high specific capacitance of 1500 F cm-3,it is one of the ideal candidate materials for the preparation of flexible f1ber electrodes.However,Ti3C2Tx nanosheets are mainly prepared by chemical etching and followed by exfoliation,and their lateral size is small and the interlayer force is weak,which makes the preparation of Ti3C2Tx fibers by wet spinning technology present certain challenges.At the same time,although the fiber supercapacitor assembled with Ti3C2Tx-based fiber electrodes can show high capacitance performance at room temperature,its device performance under severe cold or hot conditions will be severely degraded.Therefore,it is an urgent need to develop a full-temperature fiber supercapacitor with optimized balance of flexibility and specific capacitance assembled by Ti3C2Tx-based fiber electrodes.In this study,Ti3C2Tx nanosheets are used as the basic assembly unit,and Ti3C2Tx-based fiber electrodes are prepared by wet spinning technology.It is expected that the prepared Ti3C2Tx-based fiber electrode materials have both excellent electrochemical properties and high mechanical properties.Meanwhile,in order to realize the normal operation of Ti3C2Tx-based fiber supercapacitors in a wide temperature range,a new type of montmorillonite/polyvinyl alcohol(F-MMT/PVA)organic hydrogel electrolyte is developed,and a full-temperature all-solid flexible fiber supercapacitor is successfully assembled.The thesis contains five chapters.The first chapter is an introduction,the composition,classification,and the working principle of the flexible fiber supercapacitor are systematically reviewed,also the preparation and the electrochemical property of Ti3C2Tx and Ti3C2Tx-based electrode materials are discussed.Moreover,the purpose,the research content and the innovation of this research topic are proposed.Chapters 2 to 4 are experiments,results and discussions,mainly including the preparation of Ti3C2Tx/graphene(RGO)composite fiber and the all-solid asymmetric Ti3C2Tx/RGO//polyaniline(PANI)/RGO flexible fiber supercapacitor assembly,the preparation and capacitance properties research of Ti3C2Tx/aramid nanofiber(ANF)composite fiber electrode and the assembling of full temperature all-solid Ti3C2Tx/ANF flexible fiber supercapacitor.Chapter 5 is in summary.The main research contents are as follows:(1)Taking the single-layer or few-layer Ti3C2Tx nanosheets and GO nanosheets as the basic assembly unit,the liquid crystal phase GO is introduced into the Ti3C2Tx nanosheets,and the Ti3C2Tx/GO fiber electrode is prepared by wet spinning technology.Then Ti3C2Tx/GO fiber electrode is reduced in HI solution,and Ti3C2Tx/RGO fiber electrode is finally prepared.The structure,morphology and electrochemical performance of the prepared Ti3C2Tx/RGO fiber electrode are systematically characterized.At the same time,wet spinning technology is used to prepare PANI/RGO fiber electrodes.The specific volume capacitance of Ti3C2Tx/RGO fiber electrode in 1 M H2SO4 electrolyte is 415 F cm-3,and it has a good mechanical strength of 29.5 MPa.With the prepared Ti3C2Tx/RGO fiber as the negative electrode,PANI/RGO fiber as the positive electrode and PVA-H2SO4 gel as the electrolyte,the all-solid asymmetric flexible Ti3C2Tx/RGO//PANI/RGO fiber supercapacitor is assembled through the tight winding technology.The assembled device not only has a specific capacitance of 25 F cm-3,but also has a maximum volumetric energy density of 3.4 mWh cm-3 when the volu1etric power density is 10.2 mW cm-3.Also the assembled device has excellent flexibility and mechanical properties,and its specific capacitance is not significantly reduced under the condition of 500 bends or different degrees of bending.The electrode material preparation and device assembly technology will provide a new way for high energy density and the optimal balance of the asymmetric fiber supercapacitors between the mechanical flexibility and the specific capacitance.(2)With the goal of achieving the optimal balance of the capacitance and mechanical properties of Ti3C2Tx-based fiber electrodes,one-dimensional ANF will be obtained as a flexible functional additive through proton donor-assisted para-aramid fiber(PPTA)deprotonation,and two-dimensional Ti3C2T,nanosheets are used as the assembly unit,Ti3C2Tx/ANF(T/A)composite fiber electrodes with high capacitance and excellent mechanical property are prepared by using wet spinning technology in a 0.5 M FeCl2 coagulation bath,and the effect of ANF addition on the the structure,morphology,flexibility and electrochemical performance of the prepared fiber electrode are systematically studied,and the optimization balance regulary between the flexibility and specific capacitance of Ti3C2Tx/ANF(T/A)composite fiber electrode are investigated.When the amount of ANF added is 5%,the prepared T/A-5 composite fiber electrode has excellent electrochemical properties of 807 F cm-3 and high mechanical strength of 104 MPa at the same time,and an optimal balance between the flexibility and specific capacitance of Ti3C2Tx/ANF(T/A)composite fiber electrode is obtained.(3)Aiming at designing and developing all-solid-state flexible fiber supercapacitors with optimal balance between the flexibility and specific capacitance and wide working temperature window.Through the introduction of thermally stable components(F-MMT)and antifreeze aqueous electrolyte system,the traditional PVA-H2SO4 hydrogel electrolyte is modified,and F-MMT/PVA organic hydrogel electrolyte with low temperature resistance,high temperature heat resistance,light weight,outstanding flexibility and high ionic conductivity is prepared.By using Ti3C2Tx/ANF-5 fiber as the positive and negative electrodes,F-MMT/PVA organic hydrogel electrolyte as the electrolyte and separator,full-temperature all-solid-state flexible F-MMT/PVA T/A-5 fiber supercapacitor are assembled by a step-by-step immersion method.The specific capacitance of the assembled device at a current density of 0.25 A cm-3 is 295 F cm-3,and its volumetric energy density is 26.2 mWh cm-3.After 10,000 charge/discharge cycles at a current density of 5 A cm-3,the capacitance retention rate of the device is 91%.At the same time,F-MMT/PVA T/A-5 fiber supercapacitor can exhibit good flexibility and excellent capacitance performance in a wide temperature range of-40?80?,and its electrochemical performance changes little bended at different degrees and for different times.This research provides a new idea for the design and assembly of all solid-state symmetrical flexible fiber supercapacitors with optimal balance between the flexibility and specific capacitance and wide working temperature window. |
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