Lead Dioxide/Activated-carbon Hybrid Supercapacitors

As intermediate systems between conventional capacitors and batteries,supercapacitors have shown many advantageous features.While batteries are capable of storing higher energy density than supercapacitors,they deliver less power;Compared to conventional capacitors, supercapacitors can store higher energy density with tess delivered power.Supercapacitors have shown many potential applications in industrial fields,such as mobile telecommunication, information technology,consumer electronics,aviation & aerospace,military,and so on.Recently the prospect of supercapacitors with high power densities extends their application to various other novel devices such as hybrid capacitor-battery systems used in the electric vehicle,and such hybrid systems have attracted more attention throughout the world.Studies on supercapacitors are mainly focused on the preparation of high performance material and electrode assembly.This dissertation was carried out following the international frontier research,according to many literature materials.With carbon materials and lead dioxide as electrode materials for supercapacitors,by integrating various electrochemical and material preparation methods,this research work has been carried out on investigation of material preparation,electrolyte optimization,electrode preparation,capacitive property and mechanism of double-layer capacitance.The main results are as follows:1.Activated carbons have been used as electrode materials in supercapacitor.By investigating electrode preparation and capacitor assembly technology,using cyclic voltammogram, electrochemical impedance spectrum measurement and constant current charge/discharge methods,capacitive characteristics of carbon supercapacitor are studied.These researches are the basis of novel electrode materials.2.Lead dioxides were prepared by the galvanostatic method.Conditions were optimized in the preparation technology and the influence of the current density on the structure of lead dioxide electrodes investigated by using scanning electron microscope(SEM) and X-ray diffraction(XRD).Electrochemical performance of the hybrid supercapacitor by using the lead dioxide thin electrode as positive electrode,an AC electrode as negative electrode and 1.28g cm^-3 H₂SO₄ as electrolyte were characterized by using cyclic voltammetry(CV), electrochemical impedance spectroscopy(EIS) and galvanostatic charge/discharge measurements.The results showed that the hybrid capacitor also exhibited capacitance characteristics.Its capacitance was attributed to activated carbon double-layer capacitor at electrodes interfaces and redox pseudocapacitance.And it demonstrated that current density had large effect on the electrochemical performance of the lead dioxide thin electrode.The hybrid capacitor assembled with lead dioxide prepared at current density of 30 mA·cm-2 as positive electrode and an activated carbon as negative electrode delivered a discharge specific capacitance of 99.1 F·g^-1,and after 3000 cycles the specific capacitance remained 83%of the maximum value.3.Lead dioxides were prepared by the pulsed current techniques.The influence of the pulsed curent and pulsed time on the structure of lead dioxide electrodes was studied by using SEM and XRD.Electrochemical performance of the hybrid supercapacitor by using the lead dioxide thin electrode as positive electrode,an AC electrode as negative electrode and 1.28g cm^-3 H₂SO₄ as electrolyte was characterized by using CV,EIS and galvanostatic charge/discharge measurements.The results showed that the hybrid capacitor exhibited capacitance characteristics.Its capacitance was attributed to activated carbon double-layer capacitor at electrodes interfaces and redox pseudocapacitance.It was demonstrated that pulsed conditions had large effect on the electrochemical performance of the lead dioxide thin electrode.The hybrid capacitor assembled with lead dioxide prepared at pulsed current density of 25 mA·cm^-2,pulsed time and relaxation time as positive electrode and an activated carbon as negative electrode delivered a discharge specific capacitance of 109.1 F·g^-1,and after 5000 cycles the specific capacitance remained 91%of the maximum value.