Browsing by Subject "Batteries"
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Item Ab Initio Study of Nanostructures for Energy Storage(2014-05-07) Cristancho Albarracin, DahiyanaNanomaterials 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.Item Development of antimony-based anode systems for lithium-ion batteries(2015-08) Allcorn, Eric Koederitz; Manthiram, Arumugam; Goodenough, John B; Ferreira, Paulo J; Yu, Guihua; Mullins, Charles BThe superior energy storage characteristics of lithium-ion batteries have made them the state-of-the-art battery technology for the past two decades where they have been integral to the proliferation of portable electronics. Efforts to expand their application into the realms of transportation and stationary storage require additional performance enhancements, though. These enhancements will be achieved through the application of advanced new materials such as alloy anodes like antimony. Alloy anodes offer the potential for dramatic enhancement of cell capacity both gravimetrically and volumetrically due to the high lithium content in their lithiated phases. Additionally, their higher operating voltage means that their incorporation should increase cell safety, a key parameter in large-scale applications, by reducing the risk of lithium plating. The primary factor inhibiting the adoption of alloy anodes is their short cycle life brought about by the large volume change they undergo during cycling that leads to crumbling of the active material and drastic capacity loss. To overcome this issue the following mitigation techniques are applied to antimony active materials: (i) use of active-material intermetallics of M[subscript x]Sb (where M = Ni or Fe) instead of pure antimony; (ii) incorporation of active material into reinforcing active/inactive composites with Al₂O₃, TiC, and/or carbon black; (iii) reduction of active material particles to nano-scale. In addition, the use of high-energy mechanical milling allows these methods to be applied with a simple and potentially scalable synthesis procedure and yields high-density final products. The actual safety performance of antimony anodes are also analyzed due to the importance of such parameters in large-battery applications. Because antimony alone without other components is an impractical anode material, the effects on safety and thermal stability of incorporating it into intermetallic and composite structures are also investigated. The advanced nanocomposites developed in this work demonstrate excellent cycle life with good all-around performance parameters that make them viable, safer candidates to replace graphite in next generation lithium-ion batteries. Pure antimony is also shown to offer enhancement in cell safety performance relative to graphite as well, and nanocomposites based upon its use as an active material are able to retain these favorable safety characteristics.