| With the development of flexible wearable electronic devices,such as flexible displays,smart fabrics,electronic skin,they will change human's lifestyles to the large extent and is a future trend in the development of electronic devices.To meet the rapid development and practical application of flexible wearable electronic devices,the basis energy supply source for the flexible wearable electronic devices should not only ensure the excellent electrochemical performance,but also need to meet the lightweight,wearability,good breathability and so on.Among a variety of energy storage devices,flexible all-solid-state fiber supercapacitor is considered to be the promising electrochemical energy storage device,which not only has high power density,long cycle life,rapid charge-discharge ability,good safety and green pollution-free,but also possess lightweight,tiny volume and could be woven into thefabric.Graphene fiber is considered to be one of the most promising electrode materials for flexible all-solid-state fiber supercapacitor due to their excellent mechanical property and electrochemical property.However,pure graphene fibers with various structures show either good flexibility but low capacity,or high capacity but flexible deterioration due to the hybrid of other rigid pseudocapacitive materials,which is unfavorable for the construction of supercapacitors with satisfactory flexibility andhigh energy density.Therefore,how to achieve the balance between flexibility and high capacity for graphene-based fiber electrodes is an important challenge to develop high-performance flexible fiber-type supercapacitor.To solve balance problem between flexibility and high capacity for graphene-based fiber electrodes,in this thesis,RGO/Mn3O4 hybrid fibers with good flexibility and high capacitance were prepared by a scalable wet-spinning approach and followed by treating in a solution of hydrazine hydrate,in which GO with larger nanosheet size and Mn3O4 nanocrystals were used to as assembled units.By intertwining two as-prepared RGO/Mn3O4-30 flexible hybrid fiber electrodes,flexible symmetric all-solid-state fiber supercapacitor was assembled,and its mechanical and electrochemical properties were characterized.The whole thesis consisted of four chapters.The structure,classification,preparation methods,application and the challenge of fiber electrode materials and the flexible fiber supercapacitors were systematically reviewed,and also the structure,property,preparation methods and applications of graphene fiber,Mn3O4,and RGO/Mn3O4 hybrid materials were discussed in Chapter 1.Chapter 2 and Chapter 3 were the experimental parts and result discussion,which consisted of the preparation RGO/Mn3O4 hybrid fibers by the scalable wet-spinning approach and followed by treating in a solution of hydrazine hydrate in Chapter 2.High-performance flexible symmetric all-solid-state fiber supercapacitor was assembled by intertwining two RGO/Mn304 hybrid fiber electrodes,and their mechanical flexibility and capacitance performance were systematically investigated in Chapter 3.The conclusion of this thesis was given in Chapter 4.The main research works were as follows:(1)The preparation RGO/Mn3O4 hybrid fibers with excellent flexibility and high capacitance.Graphene oxide(GO)with nanosheet size larger than 20 ?m and Mn3O4 nanocrystals with a size of about 5 nm were used as assembled units,RGO/Mn3O4 hybrid fibers with excellent flexibility and high capacitance were prepared by a scalable wet-spinning approach and followed by treating in a solution of hydrazine hydrate,in which GO could be reduced into RGO,while Mn3O4 nanocrystals were maintained after hydrazine vapor reduction treatment.The prepared Mn3O4/RGO hybrid fiber electrode showed regular fibrous network structure,and this network structure was favorable for improve the transport rate of electrolyte ions in the hybrid fiber.In addition,Mn3O4 nanocrystals uniformly adhered on the graphene could not only inhibit the agglomeration of the graphene nanosheets,but also provide a large number of redox activity sites,achieving the fiber electrode material performance improvement.Moreover,the obtained RGO/Mn3O4-30 fiber electrode possessed a maximum volumetric capacitance of 311 F cm-3 at a current density of 300 mA cm-3 on the basis of maintaining the electrode good flexibility and mechanical strength.A suitable amount of Mn3O4 nanocrystals not only maintained the tensile strength and flexibility of the obtained fiber electrode,but also significantly improved its capacitance.Therefore,the balance problem between flexibility and high capacitance for graphene-based fiber electrodes was solved well.(2)The assembling and capacitance of high-performance flexible symmetric all-solid-state fiber supercapacitor.Mn3O4/RGO-30 hybrid fibers with excellent mechanical property and high capacity was used as positive electrode and negative electrode,respectively,and PVA/H3PO4 was used as gel electrolyte,high-performance flexible symmetric all-solid-state fiber supercapacitor was assembled by intertwining two RGO/Mn3O4-30 flexible hybrid fiber electrodes.The assembled flexible all-solid-state supercapacitor possessed a volumetric capacitance of 45.5 F cm-3 at a current density of 50 mA cm-3,much higher than that of pure graphene fiber all-solid-state supercapacitor,exhibited satisfactory rate capability(68%capacitance retention rate from 50 mA cm-3 increased to 1600 mA cm-3)and good cycle stability(85%of initial capacitance values after 10000 consecutive cycles).In addition,the assembled flexible all-solid-state supercapacitors not only maintained their flexibility and mechanism property after tolerate long-term and repeated bending,but also exhibited a maximum volumetric energy density of 4.05 mWh cm-3 and volumetric power density of 268 mW cm-3.Besides,the operating voltage could be extended from 0.8 V to 2.4 V by connecting three fiber supercapacitors in series at the same discharge time,and it could light up a light emission dioxide(LED)lamp,demonstrating its potential application as an efficient energy storage component for next generation flexible wearable electronics.Therefore,the introduction of Mn3O4 nanocrystals into graphene fiber can play its good pseudocapacitance and surface adhesion with graphene fiber while without seriously affecting fiber softness and mechanical strength,and the balance problem between flexibility and energy density for graphene-based fiber electrodes is solved effectively. |
PDF Full Text Request