| Supercapacitor,as a new kind of energy storage device,has attracted considerable attentions due to their high power density and long cycling life.Nowadays,supercapacitor have been widely used in electronic,new energy vehicles and other advanced technology fields.Traditional supercapacitor uses hard packaging materials to prevent leakage of liquid electrolyte.With the rapid development of flexible wearable and portable functional electronic devices,supercapacitors that can be bendable and flexible under different states have attracted more and more attentions.This thesis includes two parts.In chapter III,we prepared a high-performance carbon electrode by chemical activation of biomass corn stalk.We also tentatively fabricated a flexible solid-state capacitor with commercial carbon cloth as flexible substrate and aCS as the active electrode.In order to enhance the electrochemical capacity of commercial carbon cloth,in chapter IV,we modified the surface nature of commercial carbon cloth via an electrochemical activation method,and discussed its performance as supercapacitor electrode.Two-dimensional porous carbon materials with large surface and excellent electrochemical performance can be facilely obtained by carbonization and chemical activation of biomass corn stalk.The obtained carbon product displays two-dimentional sheet-like structure with sheet thickness of?100 nm,and the aspect ratio in the range of 500-1000.Depending on the amount of KOH used in the activation step,the specific surface area of carbon sheets varies from 388 to 1736 m2 g-1.The capacitive performance of aCS-5 in both KOH and Na2SO4 aqueous electrolytes is investigated.The aCS-5 electrode in KOH electrolyte exhibits remarkable high-rate capability due to the dramatically shortened ion pathway and more exposed external surface.While,in Na2SO4 it shows relatively lower capacitance retention but stable and extended voltage window(0-1.6 V),thus delivering a specific energy of 20.2 Wh kg-1 at a power density of 398 W kg-1.The aCS-5 with a large aspect ratio(200-500)can also serve as electrode for assembling solid-state capacitor(SSC)using PVA/KOH gel as polymer electrolyte.The SSC retains the normal capacitive performance under bent and twisted states and exhibit an unusual rate capability with an areal capacitance of 136 mF cm-2 at 0.5 mA cm-2.Commercial carbon cloth have been widely used as flexible substrates in view of its uniform texture,good electrical conductivity and light-weight property.But its specific surface area is rather low and the wettability is poor.To improve its performance as flexible substrate,we applied electrochemical oxidation-reduction method to control the surface functional groups of carbon cloth.Results from three-electrode cell showed the capacitance of activated cloth can achieve at 568 mF cm-2 at the current density of 2 mA cm-2.After electrochemical activation,the residual oxygen containing functional groups affect the conductivity of the carbon cloth,a layer of conductive ploymer PEDOT was coated on CC surface.The introduction of conductive ploymer can reduce the resistance between carbon cloth and electrolyte.As a result,specific capacitance of aCE-PEDOT was improved to 688 mF cm-2.In two-electrode cell,even at high scan rate of 3.0 V/s,the cyclic voltammetric curves still remain a good rectangular shape.After 10000 cycles,the cycling stability is remained at 99%.A flexible solid supercapacitor was fabricated with the aCS-5 coated CC as the symmetric electrode.The specific capacitance can reach 708 mF cm-2.Two identical capacitors were connected in series to widen the voltage window at 2.0 V.The two cells connected in series could easily light up five light-emitting-diode(LED),demonstrating its potential as supercapacitor electrode. |
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