Chemical and Biomolecular Engineering Theses and Dissertations

Permanent URI for this collectionhttp://hdl.handle.net/1903/2751

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Start date: 2000Subject: search.filters.subject.Energy

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    ELECTROLYTE AND INTERPHASE DESIGN FOR HIGH-ENERGY AND LONG-LIFE LITHIUM/SULFURIZED POLYACRYLONITRILE (Li/SPAN) BATTERIES
    (2024) Phan, An Le Bao; Wang, Chunsheng; Chemical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    Lithium/sulfurized polyacrylonitrile (Li/SPAN) recently emerged as a promising battery chemistry with theoretical energy density beyond traditional lithium-ion batteries, attributed to the high specific capacities of Li and SPAN. Compared to traditional sulfur-based cathodes, SPAN demonstrated superior sulfur activity/utilization and no polysulfide dissolution issue. Compared to batteries based on layered oxide cathodes, Li/SPAN shows two significant advantages: (1) high theoretical energy density (> 1000 Wh kg-1, compared to around 750 Wh kg-1 of Li/LiNi0.8Mn0.1Co0.1O2) and (2) transition-metal-free nature, which eliminates the shortcomings associated with transition metals, such as high cost, low abundance, uneven distribution on the earth and potential toxicity. The success of Li/SPAN chemistry with those two critical advantages would not only relief the range and cost anxiety persistently associated with electric vehicle (EV) applications, but also have great implications for the general energy storage market. However, current Li/SPAN batteries still fall far behind their true potential in terms of both energy density and cycle life. This dissertation aims to provide new insights into bridging the theory-practice gap of Li/SPAN batteries by appropriate interphase and comprehensive electrolyte designs. First, the effect of Li/SPAN cell design on energy density and cycle life was discussed using relevant in-house developed models. The concept of “sensitivity factor” was established and used to quantitatively analyze the influence of input parameters. It was found that the electrolyte, rather than SPAN and Li electrodes, represents the bottleneck in Li/SPAN development, which explains our motivation to focus on electrolyte study. Another remarkable finding is that although not well-perceived, electrolyte density has a great impact on Li/SPAN cell-level energy density. Second, design principles to achieve good electrode-electrolyte compatibility were explored. Novel approaches to promote the formation of more protective, inorganic-rich interphases (SEI or CEI) were proposed and validated with proper experiments, including electrochemical tests, material characterizations (such as SEM, XPS, NMR, IR, Raman), and their correlations. Finally, based on the principles discussed in previous chapters, we developed a new electrolyte that simultaneously offers good electrochemical performance (Li CE > 99.4%, Li-SPAN full-cells > 200 cycles), decent ionic conductivity (1.3 mS cm-1), low density (1.04 g mL-1), good processability (higher vapor pressure than conventional carbonates, b.p. > 140 °C), and good safety. Outlook and perspective will also be presented. Beyond Li/SPAN, we believe that our findings regarding cell design as well as electrolyte solvation structure, interphases chemistry, and their implications on electrochemical performance are also meaningful for the development of other high-energy battery chemistries.
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    Composition-Function Analyses and Design of Plasticized Solid Polymer Electrolytes for Lithium-ion Batteries
    (2023) Ludwig, Kyle Brandyn; Kofinas, Peter; Chemical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    This dissertation work examines the electrochemical properties of various solid polymer electrolytes (SPEs) through the lens of composition-function relationships. The analyses presented offer unique design perspectives for improving the performance of SPEs for use in lithium-ion batteries (LIBs). Specifically, three distinct strategies are explored to enhance the lithium ion (Li+) conductivity and reduce the electrode/electrolyte interfacial resistance, two of the major challenges of adopting SPEs as alternatives to common organic liquid electrolytes. The basis for improving ionic conductivity, in all three strategies, is the inclusion of additives in the polymer matrix to plasticize the SPE and improve ionic transport. In one strategy, an ionic liquid (IL) is used as a plasticizer to fabricate free-standing ILSPEs membranes based on a poly(ethylene oxide) (PEO) matrix with an appropriate lithium salt. Optimized ILSPE compositions were able to achieve room temperature ionic conductivity of 0.96 mS/cm, a value suitable for commercial applications, as well as long cycle life in a lithium-metal battery with a capacity of 150—175 mAh/g and >99% coulombic efficiency. In a second strategy, the IL was swapped with water as the plasticizer to fabricate PEO-based aqueous SPEs (ASPEs). The ASPEs exhibited excellent transport properties, with room temperature conductivity values of 0.68—1.75 mS/cm. Molecular dynamics simulations revealed the origin of the exceptional transport properties as the presence of highly interconnected Li+(H2O)n domains. In a final strategy, the concepts of the ILSPE and ASPE were combined through the incorporation of both IL and water into a polymer matrix. For this strategy, the polymer matrix was also changed from PEO to polyacrylonitrile (PAN) to limit the effects of crystallinity and oxidation. These “hybrid aqueous/ionic liquid” SPEs (HAILSPEs) demonstrated the exceptional transport properties of the ASPE system with the improved stability and passivation of the ILSPE system. An analysis of the composition-function relationships correlated the dramatic rise in ionic conductivity to the nearly complete decoupling of ion transport from polymer chain mobility while the unique passivating properties were shown to derive from the choice of ionic liquid, with solid electrolyte interphases comprised of LiF, Li2CO3, Li2S, and Li3N.
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    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.
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    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.
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    NOVEL AQUEOUS-BASED ELECTROLYTES AND ELECTRODE SYSTEMS FOR THE NEXT GENERATION OF AQUEOUS LITHIUM-ION BATTERIES
    (2022) Eidson, Nicolas Thierry; Wang, Chunsheng; Chemical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    Aqueous Li-ion batteries are a vital component for the future electrification of society. Their extreme safety and reduced manufacturing costs could enable them to fit into many niche markets. Current aqueous Li-ion battery systems suffer from many of the same form factor restrictions as organic Li-ion batteries and rely heavily on maximizing the amount of LiTFSI in the system at the cost of important properties such as electrolyte cost, viscosity, and ionic conductivity in order to maintain the highly concentrated electrolyte classification. They are also limited by the lack of suitable anodes to replace the dominant choice of LTO. Much of the advancement in recent years has been due to the focus on improving the SEI with less attention paid to other important concerns. The goal of this research is not only to continue advancing the limits of aqueous Li-ion batteries, but to shed light on some of the other areas that are often overlooked but of equal importance. Reported here are three key advancements in the development of a novel aqueous cell chemistry for form factor, electrolyte, and anode. First is the development of a gel polymer electrolyte and gel protection layer for the fabrication of a flexible 4V aqueous Li-ion battery employing a Graphite/LCO electrode pair, with focus given to the system’s feasibility to be transitioned to industry. Second, the development of a safer hybrid electrolyte and subsequent transition from the highly concentrated electrolyte regime to the first reported localized highly concentrated hybrid aqueous/non-aqueous electrolyte. Finally, the first incorporation of TNO as an anode replacement for LTO. With the combination of this novel electrolyte and aqueous anode chemistry, a TNO/LMO full cell using a 1,4-dioxane diluted water/TEP co-solvent electrolyte provided an initial discharge capacity of 187 mAh/g reaching a Coulombic efficiency of >99.5% and a capacity retention of 92% after 90 cycles at a cycling cutoff potential of 2.8V.
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    ELECTROLYTE DESIGN FOR HIGH-ENERGY METAL BATTERIES
    (2022) Hou, Singyuk; Wang, Chunsheng; Chemical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    The demand for advanced batteries surged in the past decade because they are at the heart of several tactically important technologies, such as renewable electrification grids and electric vehicles (EVs). These technologies will progressively transform our energy consumption structure toward sustainability and alleviate the global climate crisis. Unlike consumer electronics, EVs require batteries with larger energy storage to avoid "range anxiety". According to the US Advanced Battery Consortium (USABC), breakthroughs are needed to double the battery energy density and reduce the price by 50% for EVs to be competitive in the automobile market. These stringent requirements are unlikely to be met by the Li-ion batteries (LIBs) because the charge storage limits have been reached. Metal batteries using metals as anodes require no host materials and have up to ten times higher charge storage capacities. When metals with low redox potentials (Mg, Ca, and Li) are used, new battery systems that benefit from larger capacities and high cell voltages result in over 100 % leap in energy density to satisfy the USABC's goals for EV applications. On the other hand, the scarcity of materials related to LIBs raises uncertainties and doubts in the transition to electric transportation. Metals such as Mg and Ca are highly abundant in the earth crust, which potentially ensures the reliability of the energy supply in the future.Despite the exciting prospects of metal batteries, there are knowledge gaps in understanding how the electrolyte changes the behaviors of metal plating/stripping. Although electrolytes are considered inert materials in batteries, they are indispensable in maintaining ionic transport, modulating interfacial reaction kinetics, and maintaining reversible electrode reactions through the formation of solid-electrolyte interphase (SEI). In this dissertation, I detailed our efforts to establish the microscopic understanding of the electrolyte structures, SEI components, nucleation, and growth of the electroplated metal with spectroscopic techniques and physical models. These understandings guided the design of electrolytes for reversible metal anodes in practical high-energy battery applications.
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    HIGH-SAFETY ELECTROLYTES DESIGN FOR HIGH ENERGY DENSITY BATTERY DEVICES
    (2021) Zhang, Jiaxun; Wang, Chunsheng CW; Chemical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    Recently, the market share of lithium-ion batteries (LIBs) increase rapidly in the global energy market, while accidents related to fires and explosions of LIBs reported worldwide in the past several years, thus battery safety is a vital prerequisite for battery application in our daily life. The flammable organic solvent in the electrolyte of the battery is the main source that leads to fires and explosions of batteries. Designing intrinsically safe electrolytes is the key to enhancing the safety properties of batteries. Fluorinated organic electrolytes, polymer electrolytes, and aqueous electrolytes are attractive due to their inherent non- or less-combustibles. However, the energy density, cycle stability, and battery cycle life of the LIBs using the above electrolyte systems are far from commercial batteries due to poor solid electrolyte interphase (SEI) and cathode electrolyte interphase (CEI). In this dissertation, we designed SEI/CEI on anode/cathode surfaces in fluorinated organic electrolytes, polymer electrolytes, and aqueous electrolytes to enhance battery performance. Specifically, 1. By building a highly stable CEI on a high-voltage LiCoO2 cathode, we improved the energy density of fluorinated organic electrolyte batteries. 2. By introducing UV-curable polymer into the organic electrolytes, we lowered the flammability of the sodium batteries and enhanced the energy density of the sodium battery system with stable CEI on sodium cathode. 3. By limiting the water activity in the bulk electrolyte and constructing an effective SEI layer on anode surface, we expanded the electrochemical stability window of the aqueous electrolytes. We seek to understand the working mechanism of SEI/CEI in different high-safety electrolyte systems. The corresponding electrochemistry, thermodynamics, kinetics, and reaction reversibility are studied in this work.
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    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.
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    TUNING THE STRUCTURE AND CHEMISTRY OF SOLID OXIDE FUEL CELL ELECTRODES FOR HIGH PERFORMANCE AND STABLE OPERATION
    (2021) Horlick, Samuel; Wachsman, Eric D; Chemical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    Their reliability, fuel-flexibility, and high specific power make solid oxide fuel cells (SOFCs) promising next-generation power conversion devices. These advantages are theoretically attainable, but current material and structural limitations on the electrodes restrict the true potential of SOFCs on a cell level. Furthermore, ceramic processing challenges hinder the large-scale implementation of SOFCs. Here, SOFC electrodes are redesigned to develop the device closer to its theoretical potential. First, a fundamental investigation into the nature of exsolution materials provides a platform for controlling electrocatalyst properties such as: particle size, population, composition, and contact angle on host. Next, this knowledge is used to design a stable and active anode for the first ever exsolution-anode-supported SOFC and the practical limitations of this approach are identified to lead future research routes. In parallel to this study, a new method for synthesizing cheap, effective catalysts is developed to enable long-term SOFC operation with hydrocarbon fuel without sacrificing performance. Additionally, a systematic study identifies oxygen diffusion as the rate limiting step in the high current regime, and when this limitation is removed with improved system and electrode design, world-class power densities are achieved. Finally, a methodical investigation into ceramic processing of full-scale (5x5cm) SOFCs uncovers that cell flatness can be improved by optimizing green-tape compositions, sintering time/rate/temperatures, and top plate selection. Likewise, electrolyte quality depends on the top plate used in sintering and a light-weight YSZ-coated top plate gives the best balance between flatness and electrolyte quality.
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    DIRECT NON-OXIDATIVE METHANE CONVERSION VIA H2-PERMEABLE TUBULAR CERAMIC MEMBRANE REACTOR
    (2019) Sakbodin, Mann; Liu, Dongxia; Wachsman, Eric D.; Chemical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    Conversion of methane to higher hydrocarbons has the potential as the substitute for liquid petroleum in petrochemical and other chemical industries. Direct non-oxidative methane conversion (DNMC) reaction has attracted much attention given its unique capability to convert methane into C2 (acetylene, ethylene, and ethane), aromatics, and hydrogen, while circumventing the intermediate energy intensive steps found in the conventional indirect “syngas” routes. In addition, DNMC has better atom efficiency compared to the indirect routes since COx products can be avoided. However, the main drawbacks of the DNMC reaction are due to the low methane equilibrium conversion, high endothermicity, and high rate of carbon formation. This dissertation aims to development a novel catalyst/membrane system to circumvent the limitations of the DNMC reaction for the efficient and effective hydrocarbons production. The single iron sites confined in the lattice of silica matrix (Fe/SiO2) is an emerging methane activation catalyst for the DNMC reaction. By coupling the Fe/SiO2 catalyst with the H2-permeable tubular ceramic membrane reactor, part of the hydrogen produced from the DNMC reaction can be removed from the effluent gas, which shifts the equilibrium of the reaction to the product side, and in turn, increases the methane conversion. In addition, different sweep gases (H2, air, O2) can be used to promote different additional capabilities of the membrane reactors. The product distribution of the DMNC reaction can be tuned by either removing or adding H2 to the DNMC reaction. Dual production of higher hydrocarbons and CO (or syngas) from two major global greenhouse gases can be achieved when CO2 is used as the sweep gas. On one side of the membrane tube, CH4 upgrading to C2+ hydrocarbons was realized via DNMC reaction over the Fe/SiO2 catalyst, with co-production of H2 gas. On the opposite side, the hydrogen permeate reacted with CO2 sweep to form CO and H2O via the RWGS reaction. Autothermal operation of the membrane reactor is potentially feasible by providing the heat required for the endothermic DNMC reaction from the heat released from the combustion of permeated H2 when O2 is used as sweep gas. In addition, a dual DNMC reactor and H2-permeable membrane system was proposed in order to enhance the production of aromatics from CH4, with pure H2 as a beneficial byproduct. By recycling the effluent gas to the DMNC reactor after partial H2 removal, in certain conditions, the aromatics yield reached >50%, which is significantly higher than single-pass results.