ADVANCED CARBON-BASED NANOCOMPOSITE CATHODES FOR ENERGY HARVESTING AND STORAGE

Abstract

Cathodes are one of the most important components of energy generation/storage devices. In dye-sensitized solar cells (DSSCs) and photocapacitors, cathodes are critical in determining the cell’s properties such as the capacity, solar efficiency, and power. In the case of lithium-ion batteries (LIBs), the type of cathode defines the capacity and operating voltage of the cells, and thereby the energy and power, as well as the cycle lifetime. Conventional DSSC cathode, Pt-foil, is expensive and corrodes in the electrolytes, while recently developed photocapacitor cathodes suffer from low-voltage operation and cannot be assembled into compact devices. Current LIB cathodes use toxic chemicals like N-Methyl-2-pyrrolidone (NMP) during fabrication, have low capacity and low power, and are susceptible to thermal runaway. This dissertation covers the fabrication and performance evaluation of novel cathodes made up of 3D nanostructured carbon nanotubes (CNTs) as nanowires of extremely high surface area for the incorporation of active nanomaterials to achieve enhanced performances. Vertically aligned 3D CNT cathode yielded higher open circuit potential, short circuit current, and solar efficiency than the Pt-cathode inside the DSSC. High charging voltage and compactness were achieved with MnO2 deposited 3D CNT cathode in the photocapacitors. A novel high capacity LIB cathode material, Li2FexMnyCozSiO4, was synthesized and incorporated into a new cathode material host (CNT/Graphite foil). Additionally, a new technique, in-situ synthesis of LiFePO4 on 3D CNTs, to fabricate high capacity and power cathodes was developed and excellent performance was demonstrated by electrical characterization.