Date of Award

5-2018

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Physics and Astronomy

Committee Member

Dr. Apparao M. Rao, Committee

Committee Member

Chair Dr. Ramakrishna Podila

Committee Member

Dr. George Chumanov

Committee Member

Dr. Terry Tritt

Abstract

Since their inception, carbon nanomaterials have been exploited for use in energy storage. The discovery of carbon nanotubes and the later isolation of graphene opened new avenues in electrode research for batteries and electric double layer capacitors (EDLCs). Their combination of flexibility, mechanical robustness, and electronic conductivity make them ideal for use as active materials and additives. My research has focused on the synthesis and implementation of helical carbon nanotubes (HCNTs) for supercapacitors and few-layer graphene in the form of graphene foam (GF) for aluminum-ion batteries. The presence of defects and dopants was controlled in each system to determine how they relate to the performance of the electrode materials. For each material, Raman spectroscopy served as a key analytical tool. Over the past two decades, the Raman modes of carbon nanotubes and graphene have been well characterized and their relation to various aspects of the graphitic lattice such as defect density, dopant type, and lattice constants have been determined. I used these characteristics to correlate material properties to electrode performance. In the first chapter, I give an overview of the properties and energy storage applications of graphene and carbon nanotubes. The second chapter concerns the basic information needed to understand the electrochemical and spectroscopic methods used to analyze the samples, as well as the instrumentation and equipment used for measurements. In the third chapter, I discuss graphene foam cathodes as used in aluminum-ion batteries. For the graphene foam studies, the methods of producing the foams and Al-ion battery components were optimized before beginning electrochemical characterization, and are described in section 3.1.2. The intercalation process of the chloroaluminate anions was studied by in situ Raman spectroscopy applied to charge/discharge cycling of the cells. The role of surface defects and nitrogen dopants in the performance of few-layer graphene was studied using this method and correlated to performance using several electrochemical techniques. The fourth and final chapter details my work with HCNTs. I first synthesized them using chemical vapor deposition methods which are commensurate with scalable processing, as described in section 4.2. They were prepared for electrochemical testing in two forms: vertically aligned arrays of various heights on metal substrates and freestanding entangled carpets known as buckypapers. They were then characterized spectroscopically and electrochemically and found to possess superior performance to that of linear carbon nanotube analogues. The HCNT buckypapers were also found to be superior scaffolds for polymer composites by virtue of retaining a greater mass loading of polymer, leading to improved capacitance.

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