The Performance Of PbO₂ And PbO₂/AC Super-Capacitor

Lead acid batteries have more than 150 years of history since its invention in 1859. This well-developed energy storage technology has been attracted a lot of interest since the various applications in emergency back-up power source, power battery, and electric vehicle. However, this technology faces serious challenge under high rate parte state of charge(HRPSo C) due to the irreversible sulphating process during the cycling, therefore limiting its employment as energy storage system in the field of clean energy, such as hybrid electric vehicle, wind energy, and solar energy. The super-battery as the third generation lead-carbon battery, has been extensively studied since the performances since 1990. In this thesis, super-capacitor(SC) has been fabricated based on carbon foam as substrate. A thin film of Pb O2 as anode is deposited on a carbon foam substrate using pulse electrodeposition method, and then combined with activated carbon(AC) to form a supercapacitor. This research aims to realize the applications in hybrid and electric vehicles by combining the advantage of lead-acid battery and super-capacitor. The main topics in this thesis include:1. The physical and electrochemical properties of AC have been characterized in detail on different substrates and in electrolytes with cyclic voltammetry, constant current charging-discharging, and electrochemical impedance spectroscopy. These study are the basis of novel electrode materials.2. A lead dioxide thin film was deposited on carbon foam substrate by the pulse electrodeposition method, and the structure and surface morphology were characterized using Xray diffraction(XRD) and scanning electron microscopy(SEM). It is clear that the quality of film was affected by the temperature, duty ratio, and p H value. A film with rough crystalline structure is formed when the temperature increasing to 60℃ and duty ratio keeping constant, since the polarization of the electrode significantly reduced. The variation of duty ratio has different influences on various materials, when prolonging the turn-off time the size of form Pb O2 crystalline grain was reduced. p H value influencing the crystal structure of the formed material. A tetragonal(β) and orthorhombic(α) configuration could be obtained in an acidic and alkaline condition, respectively. Under condition of 60℃, 25% duty ratio, acidic and current density of 0.1 A/cm2,the electro-deposition sample showed a better performance.These results are compared with a commercial lead dioxide has been used to produce electrodes using conventional battery preparation method.3. Pb O2/H2SO4/AC super-capacitor with carbon foam as a current collector, has been investigate by cyclic voltammetry, constant current charging and discharging, and electrochemical impedance spectroscopy. The capacitance was at 92 F/g and 80 F/g, when the current density was 200 and 800 m A/g, respectively. More importantly, under a 200 m A/g current density this material still retains more than 85% of its specific capacitance after 8000 continuous charge–discharge cycles.