Ab Initio Study of Nanostructures for Energy Storage

Abstract

Nanomaterials are expected to overcome the challenges imposed from bulk materials in the design of electronic devices. With the help of nanotechnology smaller, lighter, and more energy efficient materials can be used in the development of smart nanodevices. The goal of this research is to characterize the chemical, electrical, and mechanical properties of nanostructures for energy conversion and storage. In this dissertation, three materials are studied at nano level using theoretical calculations: carbon nanotubes (CNTs), lithium silicon (Li_(4n)Si_(n)), and polyvinyl alcohol (PVA). The coupling of mechanical and electronic properties of carbon nanotubes are studied, we estimate a modulus of elasticity of 1.3 TPa and find that the mechanism of CNT structure deformation is chirality dependent. Armchair and chiral nanotubes have ductile deformation fracture while zigzag have both ductile and brittle. Furthermore, the HOMO-LUMO gap of CNT increases under plastic deformation. We conclude that mechanical forces affect the electromagnetic absorption properties of CNTs.

Silicon has been proposed as a promising material for anodes in Li ion batteries; a layer called: the solid electrolyte interphase (SEI) is formed on the electrodes during charging process that may restrict the ion mobility. Preliminary electrical characterization shows the external potential effects of SEI on electron transport as a function of SEI thickness. Furthermore, the rotation of the Li_(2)O molecules in SEI plays a big role in the electron transport in Li-Ion Batteries.

Mechanical and thermal properties of polyvinyl alcohol (PVA) are characterized using in situ X-ray photoelectron spectroscopy (XPS) and theoretical calculations. It is found that the carbon peaks in PVA shifted under mechanical and thermal stretching. At different temperatures, the C-O bond was the most stable carbon group than others. We find that Hartree-Fock/10-31G (d) reproduces the binding energy of core carbon electrons, which is enough to characterize bonds and corroborate the spectroscopic analysis.