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ItemCharacterizing Solid State Battery Degradation Using Optical Microscopy and Operando X-Ray Tomography(Georgia Institute of Technology, 2022-05) Prakash, DhruvThe implementation of solid-state electrolytes (SSEs) into lithium-ion batteries shows much promise in enabling the use of higher energy density anodes, such as pure lithium metal. However, the implementation of SSEs and lithium metal anodes in lithium-ion batteries is currently not possible due to degradation mechanisms that lead to premature failure of the battery. These mechanisms, such as the formation of a new phase known as the interphase and the growth of lithium metal dendrites, are initiated at the interface between the anode and electrolyte and are linked to the current density at which the battery is cycled. Reported are two methods of characterizing the interfacial degradation phenomena that occur between lithium metal anodes and the SSE Li10SnP2S12 (LSPS). A novel symmetric battery setup was developed to allow an operando optical microscopy study of the lithium metal and SSE interface as charge was passed through the battery. Though this characterization method presented challenges, interphase formation and dendrite growth were both observed. Further, operando x-ray computed tomography of a novel cell geometry provided detailed three dimensional scans that also showed evidence of interphase growth and dendrite formation. Additionally, interfacial void formation was identified, indicating a loss of contact that increases current density. These results provide insight into the failure of solid-state batteries and show how operando optical microscopy and x-ray tomography can be used to gain a more complete understanding of the degradation of higher energy density lithium-ion batteries.
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ItemCompositional analysis of laser welds in a Cu46.5Zr46.5A7 glass forming alloy(Georgia Institute of Technology, 2021-12) Holberton, Harrison TylerLaser additive manufacturing is a promising manufacturing method of bulk metallic glasses. Study and understanding of the heat affected zone and fusion zones are crucial in developing this manufacturing technique. A cast Cu46.5Zr46.5A7 sample was processed at laser powers and scan speeds varying from 75-370W and 100-900 mm/s respectively to determine the effects of processing parameters on weld composition for use in additive manufacturing. Copper content was found to generally decrease through the weld fusion zone, and increase through the heat affected zone. Zinc was unexpectedly present in analysis. Cracking occurred at significantly different linear energy densities and appeared to correlate more strongly with laser power at these parameters, supporting previous research that using energy density alone to predict additive manufacturing processes.
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ItemREDUCING INTERFACIAL RESISTANCE OF LI-ION BATTERIES THROUGH ATOMIC LAYER DEPOSITION(Georgia Institute of Technology, 2021-12) Lee, Hae WonThe attention to solid state batteries are increasing as electrical vehicles start to dominate automobile industry. Solid-state batteries (SSBs) are type of Li-ion batteries that have solid medium. They are regarded as the next-generation energy storage device for electric vehicles because they can potentially solve the problems of conventional Li-ion batteries. In conventional Li-ion batteries, when delivered in high energy densities, they had extremely high possibility for inflammation due to the presence of flammable liquid organic electrolytes. Also, though the use of Li metal anode may significantly increase energy density, likelihood of short circuiting the cell due to the growth of Li dendrites prevents the commercialization of Li-ion batteries with Li anodes. Thus, in order to provide safer and higher energy batteries, SSBs with nonflammable and mechanically robust SSEs which may suppress Li dendrite growth came up as an alternative solution. However, there are new challenges that need to be overcome for SSBs. Not only are they more expensive than conventional Li-ion batteries, but due to solid-characteristic of the electrolyte, SSBs have critical flaw of high resistance at the SSE-electrode interfaces. The performance of SSBs in high temperature environment may be safer, but the thick SSE membrane and low active loading with the electrodes do not show better performance when compared to the liquid electrolyte cells. To enhance the battery performance, the interfacial resistance in SSBs needs to be reduced. Therefore, the focus of our lab is to come up with a novel coating method that has the least interfacial resistance. This new study will utilize the atomic layer deposition (ALD) technique to coat metal oxides on electrodes and enhance the battery performance, as previous research by many scientists has already proven that metal oxide coatings are effective at reducing the interfacial resistance in SSBs.
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ItemAn Investigation into the Glass Transition Temperature of Vapor Phase Infiltrated Organic-Inorganic Hybrid Materials(Georgia Institute of Technology, 2021-05) Bamford, JamesGlass transition temperature (Tg) is a fundamental property of a polymer that defines its upper service temperature for structural applications and is reflective of its physicochemical features. We are interested in how vapor phase infiltration (VPI), which infuses polymers with inorganic species to create hybrid materials, affects the glass transition temperature of a material. We examine Al2O3 VPI into poly(styrene-co-2-hydroxyethyl methacrylate) (PS-r-PHEMA) using trimethylaluminum (TMA) and water precursors. Our VPI precursors are selected to be unreactive towards the styrene monomer units and highly reactive towards the HEMA monomer units. Experiments were conducted on PS-r-PHEMA thin films (200 nm) spun-cast onto silicon wafers and infiltrated at 100°C with 4 hr. exposure times. Copolymers with varying fractions of HEMA units were investigated, from 0 mole % to 20.2 mole % HEMA. Volumetric swelling of the films after VPI and aluminum oxide film thicknesses after pyrolysis both confirmed higher metal oxide loading with higher fraction HEMA units. Tg was measured using a spectroscopic ellipsometer with a heating unit. We find that the glass transition temperature increases significantly with metal oxide loading. Copolymers with 0.0%, 3.0%, 7.7%, 11.5%, and 20.2% HEMA units experienced 6°C, 8°C, 22°C, 37°C, and 46°C increases in Tg respectively. Changes in Tg at low HEMA composition fit the Fox-Loshaek model for crosslinking phenomena which, along with a dissolution study on these materials, suggests that VPI alumina crosslinks PS-r-PHEMA. We conclude that VPI may be useful as a crosslinking process for designing the thermophysical and thermochemical properties of polymer thin films, fibers, and fabrics.
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ItemExtent of UV Curing in Highly Loaded Systems for Direct Ink Writing(Georgia Institute of Technology, 2021-05) Adams, Zachary KennethThis study investigates the solidification of material 3D-printed via direct ink writing. This material, consisting of monomers, a photoinitiator and silicon microspheres was extruded onto a printing bed. The material was then irradiated with ultraviolet light to polymerize the monomers. Curing time and thickness of the material were varied in order to determine their effect on the solidification process. Quantification of the extent of cure was done using Fourier transform infrared spectroscopy. The data collected show that the degree of conversion tends to decrease as curing time decreases, but the data is inconclusive as to the specific relationship between time and degree of cure. However, due to a combination of a long method development process and the coronavirus pandemic, work on this project was halted before this trend could be definitely proven.