Construction And Electrochemical Properties Of Fibrous Devices Based On Twodimensional Nanomaterials

In recent years,fibrous electronic devices have attracted wide attention because of their small size,light weight,good flexibility and knittability.The continuous development of fibrous sensors,display devices and energy harvesting devices put forward higher requirements for corresponding energy storage units.Fibrous supercapacitors not only have simple structure,fast current response,high power density,reliable cycle stability and safety,but also can maintain stable energy output under the condition of mechanical deformation.Therefore,fibrous supercapacitors are very suitable for direct application in wearable and embedded electronics and smart fabrics as energy storage devices.At present,fibrous supercapacitors still have some problems,such as poor electrochemical performance,low tensile strength and single function.Hence,we took graphene and MXene nanosheets as the basic structural units and prepared macroscopic assembled fibers with wet spinning technology,which were then used as electrodes to construct fibrous supercapacitors.The major contents are following:(1)An asymmetric fibrous supercapacitor with coaxial structure was constructed using graphene-based fiber as electrode.The graphene/Mn O₂ hybrid fibers were prepared by wet spinning technology by adding manganese dioxide nanorods into the graphite oxide liquid crystal.In the process of charge and discharge,the redox reaction between the Mn O₂ nanorods and the electrolyte can effectively improve the volume specific capacitance of the fiber electrode,which can reach up to 473 F cm^-3.Afterwards,using the hybrid fiber as inner electrode,an asymmetric fibrous supercapacitor with coaxial structure was constructed by dip-coating the electrolyte layer and the graphene outer electrode.The potential window of the device was up to 1.6 V,which is attributed to the asymmetric structure.Due to the high volume utilization and low charge transfer resistance of the coaxial structure,the volumetric energy density of the fibrous device is up to 8.44 m Wh cm^-3.(2)A stretchable fibrous supercapacitor was constructed with graphite oxide based elastic fiber as electrodes.The GO/CNTs/TPU elastic conductive fibers were prepared continuously by wet spinning technique by adding polyurethane elastomer into the fiber electrode.The hybrid fiber has a high electrical conductivity(342 S m^-1)and can be stretched over 200%,while also shows a high specific capacitance(36.45 F cm^-3)due to its abundant porous.Then,an all-solid fibrous supercapacitor was assembled using the hybrid fiber as the electrode.After 5000 cycles,the capacitance can still maintain97%of the initial,showing good cycle stability.What's more,the device can be stretched to more than 50%with stable electrochemical performance.(3)In order to obtain a higher electrochemical activity fiber electrode,pure Ti₃C₂T_x MXene fibers were prepared.Pure Ti₃C₂T_x fibers were prepared by liquid crystals,which were obtained by dispersing Ti₃C₂T_x nanosheets into deinoized water at a high concentration.Furthermore,the strength and electrical conductivity of the fibers were increased by hydroiodic acid treatment,reaching 290 MPa and 9800 S cm^-1,respectively.In addition,the electrochemical energy storage capacity of Ti₃C₂T_x fibers was up to 950 F cm^-3,which is much higher than that of graphene-based fibers.Then Ti₃C₂T_x MXene fibers were used as electrodes to construct a biological device,in which the Ti₃C₂T_x fibers can carry electrical signals with precision and realize the communication between the functional signal generator and the beetle.(4)Multifunctional fibrous devices were fabricated using MXene-based stretchable fiber as electrodes.The MXene/CNTs/TPU elastic fiber electrode was prepared by wet spinning technique and can be stretched to 200%and the resistance change rate in the stretching process was less than 0.1,which indicates that the hybrid fiber shows good mechanical and electrical stability.Then,a stretchable fibrous supercapacitor was assembled with the hybrid fiber as the electrodes.The device showed good rate ability and could be stretched up to 50%.Based on the supercapacitor,a flexible strain sensor was further constructed and realized the integration of energy storage and sensing functions on a single device.In conclusion,in this paper,based two-dimensional nanomaterials ordered macroscopic fibers electrodes,the high energy storage and versatility of fibrous devices were realized by structural design and multi-component doping.