Theses and Dissertations from UMD
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New submissions to the thesis/dissertation collections are added automatically as they are received from the Graduate School. Currently, the Graduate School deposits all theses and dissertations from a given semester after the official graduation date. This means that there may be up to a 4 month delay in the appearance of a give thesis/dissertation in DRUM
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Item ASSESSING THE IMPACT OF ELECTROCHEMICAL-MECHANICAL COUPLING ON CURRENT DISTRIBUTION AND DENDRITE PREVENTION IN SOLID-STATE ALKALI METAL BATTERIES(2023) Carmona, Eric Alvaro; Albertus, Paul; Chemical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The relationship between mechanical stress states and interfacial electrochemical thermodynamics of Li metal/Li6.5La3Zr1.5Ta0.5O12 and Na metal/Na-β”-Al2O3 systems are examined in two experimental configurations with an applied uniaxial load; the solid electrolytes were pellets and the metal electrodes high-aspect-ratio electrodes. Our experimental results demonstrate that (1) the change in equilibrium potential at the metal/electrolyte interface, when stress is applied to the metal electrode, is linearly proportional to the molar volume of the metal electrode, and (2) the mechanical stress in the electrolyte has negligible effect on the equilibrium potential for an experimental setup in which the electrolyte is stressed and the electrode is left unstressed. Solid mechanics modeling of a metal electrode on a solid electrolyte pellet indicates that pressure and normal stress are within ~0.5 MPa of each other for the high aspect ratio (~1:100 thickness:diameter in our study) Li metal electrodes under loads that exceed yield conditions. To assess the effect of electrochemical-mechanical coupling on current distributions at Li/single-ion conducting solid ceramic electrolyte interfaces containing a parameterized interfacial geometric asperity, we develop a coupled electrochemical-mechanical model and carefully distinguish between the thermodynamic and kinetic effects of interfacial mechanics on the current distribution. We find that with an elastic-perfectly plastic model for Li metal, and experimentally relevant mechanical initial and boundary conditions, the stress variations along the interface for experimentally relevant stack pressures and interfacial geometries are small (e.g., <1 MPa), resulting in a small or negligible influence of the interfacial mechanical state on the interfacial current distribution for both plating and stripping. However, we find that the current distribution is sensitive to interface geometry, with sharper (i.e., smaller tip radius of curvature) asperities experiencing greater current focusing. In addition, the effect on the current distribution of an identically sized lithium peak vs. valley geometry is not the same. These interfacial geometry effects may lead to void formation on both stripping and plating and at both Li peaks and valleys. This work advances the quantitative understanding of alkali metal dendrite formation within incipient cracks and their subsequent growth, and pore formation upon stripping, both situations where properly accounting for the impact of mechanical state on the equilibrium potential can be of critical importance for calculating the current distribution. The presence of high-curvature interface geometry asperities provides an additional perspective on the superior cycling performance of flat, film-based separators (e.g., sputtered LiPON) versus particle-based separators (e.g., polycrystalline LLZO) in some conditions.Item Assessing the Thermal Safety and Thermochemistry of Lithium Metal All-Solid-State Batteries Through Differential Scanning Calorimetry and Modeling(2023) Johnson, Nathan Brenner; Albertus, Paul; Chemical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Solid-state batteries are often considered to have superior safety compared to their liquid electrolyte counterparts, but further analysis is needed, especially because the desired higher specific energy of a solid-state lithium metal battery results in a higher potential temperature rise from the electrical energy in the cell. Safety is a multi-faceted issue that should be carefully assessed. We build "all-inclusive microcell" Differential Scanning Calorimetry samples that include all cell stack layers for a Li0.43CoO2 | Li7La3Zr2O12 | Li cell in commercially relevant material ratios (e.g. capacity matched electrodes) and gather heat flow data. From this data, we use thermodynamically calculated enthalpies of reactions for this cell chemistry to predict key points in cell thermal runaway (e.g., onset temperature, maximum temperature) and assess battery safety at the materials stage of cell development. We construct a model of the temperature rise during a thermal ramp test and short circuit in a large-format solid-state Li0.43CoO2 | Li7La3Zr2O12 | Li battery based on microcell heat flow measurements. Our model shows self-heating onset temperatures at ∼200-250°C, due to O2 released from the metal oxide cathode. Cascading exothermic reactions may drive the cell temperature during thermal runaway to ∼1000 °C in our model, comparable to temperature rise from high-energy Li-ion cells, but subject to key assumptions such as O2 reacting with Li. Higher energy density cathode materials such as LiNi0.8Co0.15Al0.05O2 in our model show peak temperatures >1300°C. Transport of O2 or Li through the solid-state separator (e.g., through cracks), and the passivation of Li metal by solid products such as Li2O, are key determinants of the peak temperature. Our work demonstrates the critical importance of the management of molten Li and O2 gas within the cell, and the importance of future modeling and experimental work to quantify the rate of the 2Li+1/2O2→Li2O reaction, and others, within a large format Li metal solid-state battery.Item First Principle Computational Study of Fast Ionic Conductors(2018) He, Xingfeng; Mo, Yifei; Material Science and Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Fast ionic conductors have great potential to enable novel technologies in energy storage and conversion. However, it is not yet understood why only a few materials can deliver exceptionally higher ionic conductivity than typical solids or how on can design fast ion conductors following simple principles. In this dissertation, I applied first principles computational method to understanding the fast ionic diffusion within fast ionic conductors and I demonstrated a conceptually simple framework for guiding the design of super-ionic conductor materials. I studied Na0.5Bi0.5TiO3 (NBT) as the model material for oxygen ionic conductor. The structure-property relationship of the NBT materials is established. Based on the newly gained materials understanding, our first principles computation predicted that Na and K were promising dopants to increase oxygen ionic conductivity. The newly designed NBT materials with A-site Na and K substituted A sites exhibited a many-fold increase in the ionic conductivity at 900K comparing to that in the experimental compound. We demonstrated that the concerted migration mechanism with low energy barrier is the universal mechanism of fast ionic diffusion in a broad range of ionic conducting materials. Our theory provides a conceptually simple framework for guiding the design of super-ionic conductor materials, that is, inserting mobile ions into high-energy sites to activate concerted ion conduction with lower migration barriers. We demonstrated this strategy by designing a number of novel fast Li-ion conducting materials to activate concerted migration with reduced diffusion barrier. We identified the common features of crystal structural framework for lithium SICs. Based on the determined attributes, we performed a high-throughput screening of all lithium-containing oxide and sulfide compounds. The screening revealed several crystal structures that are potential to be fast ion conductors. Through aliovalent doping, we modified the Li content of these structures which resulting in different Li sublattice within the structure and we found a number of lithium super- ionic conductors that are predicted to have Li+ conductivities greater than 0.1 mS/cm at 300K.Item Exploration of Lithium Ion Binding to Magnesium Bound Adenosine Triphosphate and Its Implications for Bipolar Disorder(2015) Briggs, Katharine Therese; Marino, John P.; Biology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Lithium carbonate, a drug for the treatment of Bipolar Disorder, provides mood stability to treat an illness that causes recurrent episodes of mania and/or depression. The mechanism by which lithium acts to elicit these psychological changes remains unknown. Interestingly, this small bio-active salt has been shown to reduce the risk of suicide, and appears to lower the incidence of Alzheimer’s disease. It has been proposed that lithium inhibits magnesium-dependent enzymes; however, there is no consensus as to how this occurs. Based on high resolution 7Li, 23Na, and 31P T1 and Paramagnetic Relaxation Enhancement (PRE) Nuclear Magnetic Resonance (NMR) methods, which can be used to characterize the association of lithium (Li+) at magnesium (Mg2+)-phosphorus chelation sites, we have identified a ATP•Mg•Li complex. The lithium binding affinity to form this complex is relatively high compared to other monovalent cations, with a Kd < 1 mM, and biologically relevant considering that at the typical dosing of Li+, physiological concentrations of Mg and ATP are in the 0.6 – 2.5 mM range. This has led us to propose a mechanism of action for lithium based on the formation of Mg•Li-complexes at dehydrated magnesium-phosphate sites and perhaps a role for ATP•Mg as a physiological carrier for Li+. To test this model experimentally in the context of relevant ATP-protein binding sites, we have used NMR methods to characterize the formation of the complex at ATP binding sites on albumin. Similarly, we initiated studies investigating the relevance of the ATP•Mg•Li complex to a class of purinergic receptor proteins (P2XR), since they are stimulated by purine agonists and have been implicated in Bipolar Disorder.Item A Platform Towards In Situ Stress/Strain Measurement in Lithium Ion Battery Electrodes(2012) Baron, Sergio Daniel; Ghodssi, Reza; Electrical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)This thesis demonstrates the design, fabrication and testing of a platform for in situ stress/strain measurement in lithium ion battery electrodes. The platform - consisting of a Microelectromechanical System (MEMS) chip containing an electrochemical cavity and an optical sensing element, a custom electrochemical package and an experimental setup - was successfully developed. Silicon was used as an active electrode material, and a thin-film electrochemical stack was conceived and tested. Finally, multiple experiments showed correlation between the active material volume change inside the battery and a signal change in the optical sensing element. The experimental results, combined with the MEMS implementation of the sensing element provide a promising way to evaluate electrochemical reaction-induced stress monitoring in a simple and compact fashion, while experiments are carried out in situ.Item Diffusion of Oxygen and Lithium Isotopes at a Contact between the Bushveld Complex and Metasedimentary Rock: Implications for the Timescale of Phepane Dome Diapirism(2009) Potter, Rachel; Penniston-Dorland, Sarah; Geology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Within the Eastern Lobe of the Bushveld Complex, the Phepane Dome is a circular structure of metasedimentary rock hypothesized to have formed as a wallrock diapir. To constrain the duration of Phepane Dome formation using one-dimensional diffusion models of oxygen and lithium exchange between the Bushveld Complex and the Phepane Dome, samples taken across the contact between these two lithologies were measured for their O and Li isotopic compositions and Li concentrations. Models of O and Li diffusion through melt and through aqueous fluid were fit to the data, resulting in a diffusive distance of 1.0 m for oxygen and 14.1 m for lithium. Using experimentally constrained parameters for O and Li diffusion, a range of 2 kyrs to 2 Myrs was calculated from the diffusive distances. This is consistent with previous studies of the time for crystallization of the Bushveld Complex and a model of Phepane diapir development.Item LITHIUM ISOTOPIC SYSTEMATICS OF THE CONTINENTAL CRUST(2005-12-05) Teng, Fang-Zhen; McDonough, William F; Geology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)In order to fully utilize Li isotopes as a geochemical tracer, it is necessary to characterize the Li isotopic compositions of different geological reservoirs, and quantify the magnitude of isotopic fractionations for various conditions and compositions. However, our knowledge of Li isotope geochemistry is mostly limited to the hydrosphere and mantle. Little is known about either the Li isotopic composition of the continental crust or the mechanisms by which Li isotopes are fractionated. The primary objective of this thesis is to characterize the Li isotopic composition of the continental crust. Over 50 upper crustal rocks including loess, shale, granite, and upper crustal composites, have been measured and show a limited range of Li isotopic composition (-5 to +5), with an average (0 ± 2 at 1s) that is lighter than the average upper mantle (+4 ± 2). More than 70 high-grade metamorphic rocks, including granulite xenoliths and composite samples from high-grade metamorphosed terranes have been analyzed to constrain the Li isotopic composition of the deep crust. Thirty composite samples from eight Archean terranes show mantle-like Li isotopic composition (+4 ± 1.4 (at 1σ)) while 44 granulite xenoliths display a much larger Li isotopic range from -17.9 to +15.7 with an average of -1± 7 (1σ), isotopically lighter than the mantle. These data indicate that the continental crust on average has a lighter Li isotopic composition than the upper mantle from which it was derived. Given that Li isotopes do not fractionate during high-T magmatism, juvenile crust and the mantle should have identical Li isotopic compositions. Therefore, the isotopically light continental crust is likely the result of secondary processes, e.g., weathering, metamorphism and low-T intracrustal melting. Previous studies have shown that weathering can strongly fractionate Li isotopes, with heavy Li leaching into the hydrosphere, leaving the rock residue isotopically light. Studies carried out in this thesis indicate that Li isotopes can be fractionated by diffusion, metamorphic dehydration and granite differentiation. Collectively, these processes shift the continental crust to isotopically lighter and the hydrosphere heavier than the mantle with respect to δ7Li.