| With the rapid development of flexible wearable electronic devices such as electronic sensors,flexible displays,health monitors and smart electronic skin,the requirements for flexible energy storage devices are becoming higher.Among various types of energy storage devices,all-solid-state flexible fiber supercapacitors not only have the advantages such as long cycle cycles,high power density,fast charge and discharge rates,safety and environmental protection,etc.,but also can maintain its electrochemical properties for a long time under continuous mechanical deformation such as bending,folding,twisting,and stretching,and can be directly woven into the fabric to meet the needs of wearable devices.Therefore,all-solid-state flexible fiber supercapacitors are considered to be a flexible energy storage power source with great development potential.However,how to optimize balance between high energy density and excellent mechanical property is very importance for preparing flexible fiber electrode materials and assembling its device.Fiber electrode material with high capacitance and good flexibility is key factor for determining the electrochemical performance of fiber supercapacitors.Titanium carbide(Ti3C2Tx)is a new two-dimensional material for preparing fiber electrode materials because it has a regular layered structure,high electrical conductivity,large specific surface area,and rich chemical property.However,not only the size of the Ti3C2Tx nanosheets prepared by the general method is small,but also its rigidity and low charge results in weak interaction between Ti3C2Tx nanosheets,which makes the preparation of Ti3C2Tx fiber electrodes directly from Ti3C2Tx nanosheets a great challenge.In order to prepare fiber electrode material with good electrochemical property and flexibility,conductive and flexible other organic polymers can be introduced into the precursor material,and the electrochemical property and mechanical flexibility of the obtained fiber electrode material can be greatly improved.On the basis of a rapid decrease in the electrochemical property of the fiber electrodes because the layered two-dimensional nanosheets are easy to agglomerate under dry conditions,a suitable pillaring agent will effectively block the agglomeration of the nanosheets and thereby improve the electrochemical property of the fiber electrode material during the nanosheets assembly.In addition,the low energy density bottleneck of fiber supercapacitors can be solved by widening the voltage window of the assembled devices and developing new capacitive electrode materials.In view of the many problems in the development of flexible asymmetric fiber supercapacitors,Ti3C2Tx quantum dots was selected as pillar agent because it has homogeneous property with Ti3C2Tx nanosheets,and liquid crystal phase graphene oxide nanosheets were used as the assistance for assembling Ti3C2Tx fibers in the present work.Ti3C2Tx nanosheets/Ti3C2TX quantum dots/reduced graphene oxide fiber electrode material was prepared by a wet spinning method and followed by HI reducing process,it was expected that the prepared Ti3C2Tx-based fiber electrode materials had excellent electrochemical property and good flexibility.At the same time,Ti3C2Tx nanosheets/PEDOT:PSS hybrid fibers were also prepared by using wet spinning technology in order to assemble asymmetric fiber supercapacitors to improve the energy density of devices.By using Ti3C2Tx nanosheets/Ti3C2Tx quantum dots/reduced graphene oxide fiber as positive and Ti3C2Tx nanosheets/PEDOT:PSS hybrid fiber as negative,an asymmetric all-solid-state fiber supercapacitor was assembled.The structure,morphology,the electrochemical property and mechanical property of fiber electrodes and flexible asymmetric fiber supercapacitors were systematically investigated.The full text contained five chapters.The first chapter was an introduction,the composition,classification,working principle,development trend and challenges of the flexible fiber supercapacitors were reviewed,and the advantages and disadvantages of titanium carbide as a fiber electrode material and the role of quantum dots in fiberselectrode were also analyzed.On the basis of these reviews,the significance,purpose,content and innovation for this research were proposed.Chapters 2 to 4 were experimental parts,mainly including the preparation of Ti3C2Tx quantum dots,Ti3C2Tx nanosheets/Ti3C2Tx quantum dots/reduced graphite oxide hybrid fiber electrode,and Ti3C2Tx nanosheets/PEDOT:PSS hybrid fiber electrode.All-solid-state flexible asymmetric Ti3C2Tx nanosheets/Ti3C2Tx quantum dots/RGO//Ti3C2Tx nanosheets/PEDOT:PSS fiber supercapacitor was assembled,and its electrochemical property and mechanical property were also investigated.Chapter 5 was the conclusion of the full paper.The main research contents were as follows:(1)Water bath ultrasonic method,probe ultrasonic method and fluorine-free ultrasonic method were respectively used to prepare Ti3C2Tx quantum dots.The size uniformity,dispersion property,structure and morphology of Ti3C2Tx quantum dots were characterized and analyzed on the basis of three methods,and it is determined that fluorine-free ultrasonic method was the best method for the preparation of Ti3C2Tc quantum dots.(2)By using Ti3C2Tx quantum dots with uniform size and good dispersibility as pillar agent,large-sized graphite oxide(GO)nano sheets as assistance agent,and Ti3C2Tx nanosheets delaminated in a tetramethylamine hydroxide(TMAOH)solution as assembly unit,Ti3C2Tx nanosheets/Ti3C2Tx quantum dots/reduced GO hybrid fibers with different Ti3C2Tx quantum dot contents were prepared by wet spinning technology and followed by hydroiodic acid reduction produces.The structure,morphology,mechanical properties and electrochemical properties of hybrid fibers were studied systematically.Experimental results showed that the hybrid fiber electrode had the highest volumetric capacitance(542 F cm-3)when the content of Ti3C2Tx quantum dots was 30%.At the same time,the hybrid fiber electrode has excellent flexibility and mechanical properties.Based on the characteristic and analysis of the structure,morphology,electrochemical property,and flexibility of the prepared fiber electrodes,the controlling factors for the optimal balance between the capacitance and flexibility of Ti3C2Tx-based fibers were explored.This preparation method of Ti3C2Tx nanosheets/Ti3C2Tx quantum dots/reduced GO hybrid fibers will give new idea for fabricating Ti3C2Tx-based composite fiber electrodes with high volumetric capacity and good flexibility.(3)Ti3C2Tx nanosheets/PEDOT:PSS hybrid fiber electrode(M7P3)was prepared by wet spinning technology.Asymmetric M6M3RG1//M7P3 fiber supercapacitor was assembled by using Ti3C2Txxnanosheets/Ti3C2Tx quantum dots/reduced GO(M6M3RG1)hybrid fiber as positive electrode and Ti3C2Tx nanosheets/PEDOT:PSS(M7P3)hybrid fiber as negative electrode,and PVA/H2SO4 solution as gel electrolyte.The energy storage and mechanical properties were studied systematically.The results showed that the operating voltage window of the asymmetric fiber supercapacitor can be widened to 1.5 V,and the maximum volume energy density can reach 16.6 mWh cm-3.The asymmetric supercapacitor not only had good electrochemical properties,but also showed excellent mechanical properties.After different bending angles and repeated bending for many times,the electrochemical properties of the asymmetric supercapacitor did not change significantly.Based on the characteristic and analysis of the structure,morphology,electrochemical property and flexibilityof asymmetric flexible all-solid-state M6M3RG1//M7P3 fiber supercapacitor,the control factors of assembling high volumetric energy density and good mechanical properties of Ti3C2Tx-based fiber supercapacitor were discussed,and the assembling method of Ti3C2Tx-based fiber supercapacitors with high volumetric energy density and good flexibility was developed. |
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