The Research Of Flexible Fiber-Like Electrode And Its Capacitance Performance

With the continuous development of wearable energy storage devices,fiber-like flexible supercapacitors have emerged.However,the capacitance and voltage window of the fiber-like flexible electrodes and the fiber-like supercapacitors have been reported are relatively low,so that the energy density of the single fiber-like supercapacitor is also low,which limits its practical application in the wearable field.The present work studied the aspects of substrate selection and surface modification,active material loading,and structural design of fiber-like supercapacitors.The aim is to improve the capacitance and operating voltage window of fiber-like flexible supercapacitors.Firstly,the elastic cord has been chosen as the fiber-like elastic substrate,which directly solves the problem of the large volume occupied by the fiber-like elastic supercapacitors reported so far.This study mainly uses the unique mechanical structure of the elastic cord to prepare the fiber-like flexible supercapacitor to further meet the practical application requirements of the wearable energy storage device.At the same time,we have adopted an extremely simple method to modify the surface of the elastic cord substrate,that is,to burn the elastic cord to the form melting surface,and then coat the melting surface elastic cord with the carbon nanotube film in stretching sate.In this way,the elastic flexibility of the elastic cord substrate is preserved,and the substrate is given excellent conductivity from the carbon nanotube film and the surface area of the active material is also been increased.The problem of large volume of the elastic fiberlike electrode is solved by selecting the suitable substrate.The prepared electrode has better mechanical stability and electrochemical stability,after modification of the substrate surface.Then,based on the importance of the above research on the surface modification of the substrate,it is intended to further modify the substrate surface and then load the active material with higher performance to obtain a fiber-like flexible electrode and supercapacitor with a higher capacitance.Nickel wire is used as the substrate.However,the smooth surface may make the active material directly fall off the substrate.Therefore,the nickel wire is coated on the surface of the nickel film,which retains the flexibility of the nickel wire as the base current collector,adds the roughness of the surface of the substrate and adds the surface area of the fiber-like substrate,so that it can load more active materials and the bonding about substrate with active materials is stronger.In order to further increase the capacitance,we electrodeposited Ni S as the active material on the substrate.The fiber-like electrode has stable mechanical properties,higher capacitance and longer cycling life.Finally,based on the above-described fiber-like electrode for increasing the capacitance,it is intended to further increase the operating voltage window of the fiberlike flexible supercapacitor.Increasing the capacitance and the voltage window are the two most impotant factors to increase the power density of the single fiber-like supercapacitor.We introduced the bipolar concept from the bipolar lead acid battery into the fiber-like flexible supercapacitors to achieve the aim at expanding the operating voltage window of fiber-like supercapacitors.The fiber-like supercapacitors with a bipolar structure operate at a wide operating window up to 3 V.In summary,the main research of this thesis is to improve the capacitance of fiberlike supercapacitors and widen the operating voltage window of fiber-like flexible supercapacitors,which may promote the preparation of wearable energy storage devices.