UMD Theses and Dissertations
Permanent URI for this collectionhttp://hdl.handle.net/1903/3
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 given thesis/dissertation in DRUM.
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Item DETERMINATION OF METHODS TO EFFECTIVELY STUDY INTERFACES IN SODIUM SOLID STATE BATTERIES(2021) York, Mary; Albertus, Paul S; Chemical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)As countries across the globe pledge to decrease their carbon footprint, the demand for sustainable resources has grown drastically. An increase in the energy density of electrochemical energy storage devices would advance the use of low-carbon electrical energy sources. Successful implementation of a metallic anode may allow for this increase; however, alkali metal electrodes are hindered by their reactive nature and instability at the electrode-electrolyte interface. These challenges extend to both liquid and solid electrolytes, though integration of solid electrolytes shows promise of obtaining higher energy batteries. The solid metal electrode-solid electrolyte interface is largely unexplored, but we have determined that the application of stack pressure allows for increased cyclability in all solid-state cells. Further, it is of utmost importance to achieve a pristine interface through heat treatment and polishing procedures. Data found in the literature is difficult to compare; thus, careful reporting of experimental conditions is important to efficient advancement of research.Item POLYMER ASSISTED ASSEMBLY OF INORGANIC MATERIALS FOR NEXT GENERATION BATTERIES(2019) Carter, Marcus; Rodriguez, Efrain; Chemistry; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Nanoscale materials have desirable electronic features (e.g. high surface areas, reduced mass and transport paths) that can be harnessed for a variety of technological applications. In most storage devices, there is a particular interest in nanostructured electrodes and solid-state electrolytes. A key challenge is the reproducible fabrication of these nanostructured materials. Polymers are nanoscale materials that could be used for nanoscale fabrication with improved reproducibility. In this thesis I explored two nanostructured systems using novel polymer assisted assembly methods. I fabricate a nano-structured MoS2 electrode and a nano-structured Li7La3Zr2O12 solid-state electrolyte with a garnet-type structure. A clear redox mechanism for MoS2 is currently being sought. Using our electrode, we propose a mechanism to understand the total or partial decomposition of the electrode and the formation of long soluble polysulfides. We complete a fundamental study to determine the peaks on a cyclic voltammetry curve of nanostructured MoS2. We resolve these peaks by building a novel but simple system of restacked MoS2 with a conformal polyaniline (PANI) coating. We propose that the novel coating functions by absorbing, capturing, and promoting charge transfer (oxidization and reduction) of sulfur atoms remaining at the surface. Our data suggests that PANI acts as redox mediator. Redox mediators can be molecules or solid surfaces that aid in the charge transfer to redox species, traditionally oxide species. Our findings suggest that sulfur behavior dominates the redox chemistry at 0.7 V even earlier than the proposed deep discharge. We propose that longer chain polysulfides are formed through surface mediated interactions with persistent lattice planes of MoS2. Solid-state electrolytes like cubic garnet type Li7La3Zr2O12 offer safety advantages over flammable liquid electrolytes, which is especially significant to the advancement of high energy density battery devices. Garnet however is unstable in air, suffers from low preparation efficiency and degradation into a two competitive phases, tetragonal type garnet and lithium carbonate phases, which have low conductivity. For two polymers systems, poly(styrene)-block-poly(acrylic acid), PS(0.3)-b-PAA(0.7) and PS(0.8)-b-PAA(0.2), we synthesize cubic Li7La3Zr2O12 garnet. We systematically investigate the effect of growth parameters, temperature and excess lithium content, to find the optimized synthesis conditions of 750 °C for ~5 h with 60 wt.% and 65 wt.% excess lithium salt, for the polymer systems.Item DEVELOPMENT OF VAPOR-PHASE DEPOSITED THREE DIMENSIONAL ALL-SOLID-STATE BATTERIES(2017) Pearse, Alexander John; Rubloff, Gary; Material Science and Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Thin film solid state batteries (SSBs) are an attractive energy storage technology due to their intrinsic safety, stability, and tailorable form factor. However, as thin film SSBs are typically fabricated only on planar substrates by line-of-sight deposition techniques (e.g. RF sputtering or evaporation), their areal energy storage capacity (< 1 mWh/cm2) and application space is highly limited. Moving to three dimensional architectures provides fundamentally new opportunities in power/energy areal density scaling, but requires a new fabrication process. In this thesis, we describe the development of the first solid state battery chemistry which is grown entirely by atomic layer deposition (ALD), a conformal, vapor-phase deposition technique. We first show the importance of full self-alignment of the active battery layers by measuring and modelling the effects of nonuniform architectures (i.e. does not reduce to a one-dimensional system) on the internal reaction current distribution. By fabricating electrochemical test structures for which generated electrochemical gradients are parallel to the surface, we directly quantify the insertion of lithium into a model cathode material (V2O5) using spatially-resolved x-ray photoelectron spectroscopy (XPS). Using this new technique, we show that poorly electrically contacted high aspect ratio structures show highly nonuniform reaction current distributions, which we describe using an analytical mathematical model incorporating nonlinear Tafel kinetics. A finite-element model incorporating the effects of Li-doping on the local electrical conductivity of V2O5, which was found to be important in describing the observed distributions, is also described. Next, we describe the development of a novel solid state electrolyte, lithium polyphosphazene (LPZ), grown by ALD. We explore the thermal ALD reaction between lithium tert-butoxide and diethyl phosphoramidate, which exhibits self-limiting half-reactions and a growth rate of 0.09 nm/cycle at 300C. The resulting films are primarily characterized by in-situ XPS, AFM, cyclic voltammetry, and impedance spectroscopy. The ALD reaction forms the amorphous product Li2PO2N along with residual hydrocarbon contamination, which is determined to be a promising solid electrolyte with an ionic conductivity of 6.5 × 10-7 S/cm at 35C and wide electrochemical stability window of 0-5.3 V vs. Li/Li+ . The ALD LPZ is integrated into a variety of solid state batteries to test its compatibility with common electrode materials, including LiCoO2 and LiV2O5, as well as flexible substrates. We demonstrate solid state batteries with extraordinarily thin solid state electrolytes, mitigating the moderate ionic conductivity (< 40 nm). Finally, we describe the successful integration of the ALD LPZ into the first all-ALD solid state battery stack, which is conformally deposited onto 3D micromachined silicon substrates and is fabricated entirely at or below 250C. The battery includes ALD current collectors (Ru and TiN), an electrochemically formed LiV2O5 cathode, and a novel ALD tin nitride conversion-type anode. The full cell exhibits a reversible capacity of ~35 μAh cm-2 μmLVO -1 with an average discharge voltage of ~2V. We also describe a novel fabrication process for forming all-ALD battery cells, which is challenging due to ALD’s incompatibility with conventional lithography. By growing the batteries into 3D arrays of varying aspect ratios, we demonstrate upscaling the areal capacity of the battery by approximately one order of magnitude while simultaneously improving the rate performance and round-trip efficiency.