Chemical and Biomolecular Engineering Theses and Dissertations
Permanent URI for this collectionhttp://hdl.handle.net/1903/2751
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Item LITHIUM ANODE INTERFACE DESIGN FOR ALL-SOLID-STATE LITHIUM-METAL BATTERIES(2023) Wang, Zeyi; Wang, Chunsheng; Chemical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)All-solid-state lithium-metal batteries (ASSLBs) have attracted intense interest as the next generation of energy storage devices due to their high energy density and safety. However, the Li dendrite growth and high interface resistance remain challenges due to the lack of understanding of the mechanism. Inserting a solid-electrolyte interlayer/interphase (SEI) with high lithiophobicity, high ionic conductivity, and low electronic conductivity at the Li/SSE interface can solve these problems. However, how lithiophobicity, ionic conductivity, and electronic conductivity of the interlayers affect the lithium dendrite suppression capability of the SEI has not been systematically investigated yet but is critical for ASSLBs. The main goal of this dissertation is to propose a comprehensive interface design principle/frame by considering the impacts of interlayer lithiophobicity, electronic/ionic conductivity, and porosity to Li striping/plating behavior. A combination of modeling and experiments was used to validate the design principle. The developed principle could help to resolve the electrolyte reduction and void formation issues in all-solid-state batteries. The design principle can be applied to different solid electrolytes that have different reactivity against Li, which was presented in the 3rd-6th Chapters for detail. The interlayer design principle opens opportunities to develop safe and high-energy ASSLBs.In the 3rd chapter, we investigated the correlation among ionic and electronic conductivities, lithiophobicity, and Li plating stability in the Li7N2I-Carbon Nanotube (LNI-CNT) interlayer. LNI solid electrolyte has a high ionic conductivity of 3.1 × 10–4 S cm–1 and a low electronic conductivity, high lithiophobicity, and high electrochemical stability against Li, while CNT has a high lithiophobicity, high electronic conductivity, and low tap density. Therefore, mixing LNI with CNT at different ratios can form porous lithiophobic interlayers with variable ionic and electronic conductivity. The 90 μm LNI-5% CNT interlayer enabled Li to plate on the Li/LNI-CNT interface (rather than the SSE/LNI-CNT interface) and then reversibly penetrate into/extract from the porous LNI-CNT interlayer during Li plating/stripping. The 3-dimensional Li/LNI-5% CNT interlayer contact achieved by well-controlled Li nucleation and growth enabled Li/LNI/Li cell to charge/discharge at a high current density of 4.0 mA cm-2 and a high capacity of 4.0 mAh cm-2 for > 600 hours. We also reported that a stable Li plating/stripping cycle can be achieved if the Li nucleation region in the interlayer is smaller or equal to the Li growth region in the interlayer (from the Li anode). This study represents a comprehensive interlayer design for ASSLBs with a significantly improved dendrite suppression capability and reversibility. In the 4th chapter, we develop an LNI-Mg interlayer to increase the Li dendrite suppression capability of Li//Li cells with Li6PS5Cl solid electrolyte. LNI-25%Mg interlayer can form gradient electronic conductivity inside the interlayer due to Mg migrating from the interlayer to the Li anode during activation, which can reduce the interlayer thickness and enhance the Li dendrite suppression capability. The migration of Mg was attributed to the formation of LiMg solid solution. It was found that the gradient electronic conductive LNI-Mg interlayer has better Li dendrite suppression capability than the homogeneous electronic conductive LNI-CNT interlayer due to more constrained Li plating region and mitigated electrolyte reduction. As a result, 18.5 µm LNI-25%Mg interlayer enables Li4SiO4@NMC811/LPSC/Li full cells with an areal capacity of 2.2 mAh cm-2 to be charged/discharged for 350 cycles at 60 oC with capacity retention of 82.4%. This study promotes the development of ASSLBs with higher energy density. In the 5th chapter, we combined experimental techniques and simulation methods to investigate the relationship between the interlayer’s ionic/electronic conductivity ratio, lithiophobicity, and Li plating/striping behavior in carbon-based interlayers. Firstly, we screen the carbon materials based on their ionic/electronic conductivity ratio and lithiophobicity. Li stripping/plating mechanisms were identified in different carbon materials from simulations. Secondly, we predict the critical current density of the interlayer based on the boundary condition of avoiding Li nucleation during Li plating and void formation during striping. Finally, guided by the theoretical prediction, we optimized the ionic/electronic conductivity and lithiophobicity of the carbon-based interlayer by dopping with CuO. The CuO-CNF-M (M= Mg or Ag) interlayer in situ converts to Cu-Li2O-CNF SEI/LiM structure during Li plating. The optimized SEI with ionic conductivity of 0.41 S/m and electronic conductivity of 3.3×10-3 S/m coupling with LiM anode (in-situ formed during Li plating) enables lithium-free NMC811||Cu cell to achieve long cycle life. This work represents a valuable attempt to promote the development of high-performance Li anode interlayer with a joint effort of simulations and experiments. In the 6th chapter, we design a P and I rich SEI for halide electrolytes. Halide electrolytes have the advantage of matching with high-voltage cathodes due to the high thermodynamic oxidation potential. However, they are unstable against Li anode due to their strong reactivity with Li and the formation of electronic conductive metal. In this chapter, we propose and verify critical overpotential as a criterion for Li dendrite growth. By tuning the composition of the SEI, we reduce the overpotential to lower than critical overpotential using P and I containing SEI. The P and I containing SEI with a high ionic/electronic conductivity ratio of the SEI enable Li/LYbC/Li cells to cycle at the current density of 0.1 mA cm-2 with a capacity of 0.05 mA cm-2 for more than 220 hours without a short circuit. This work represents a valuable attempt to achieve Li-stable halide electrolyte.Item VISUALIZING DYNAMICS DURING CHEMICAL REACTION DRIVEN NON – EQUILIBRIUM COLLOIDAL AND NANOPARTICLE ASSEMBLY(2023) Dissanayake Appuhamillage, Thilini Umesha; Woehl, Taylor; Chemical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Biological nano and microstructures exist far from thermodynamic equilibrium by continuous consumption of energy that allows them to reconfigure or adapt to changes in the local environment. Utilization of these non-equilibrium structure formation processes in synthetic colloidal particle and nanoparticle (NP) systems is expected to enable unprecedented control over the dynamics of synthetic active soft materials and systems that are beyond the reach of equilibrium self – assembly. In this work we adapted two non – equilibrium structure formation processes observed in biological systems, dissipative assembly and reaction diffusion instability, to generate dynamic colloidal assemblies and self-organized patterns of nanoparticles. First, we investigated how the surface chemistry and interparticle interactions between colloids changed during chemical reaction driven dissipative assembly of polystyrene colloids. A key result was the first, time dependent measurements of the dynamic colloid surface chemistry (surface charge and hydrophobicity) during dissipative assembly. Importantly, we demonstrated that thermodynamic interparticle interaction models typically used for equilibrium self-assembly are effective in describing fuel driven colloid assembly far from equilibrium. The interparticle interaction models demonstrated that electrostatic interactions controlled the concentration of particle aggregates while the strength of hydrophobic interactions determined whether colloids underwent irreversible aggregation or dissipative assembly. Next, using a correlative fluorescence microscopy and liquid phase transmission electron microscopy (LPTEM) method, we demonstrated that aminated polymer capping ligands on metal NPs undergo crosslinking and chain scission reactions as a result of formation of hydroxyl and hydrogen radicals due to electron beam induced radiolysis of water. We demonstrated that a hydroxyl radical scavenger can minimize the electron beam induced reactions in the polymers. Based on this fundamental knowledge, we introduced an instability to an initially homogenous gold NP decorated aminopolysiloxane thin film immersed in water by scanning TEM beam. Radiolysis driven polymer radical reactions of polysiloxane coupled with diffusion of radicals, polymers, and NPs caused the polymer and NP to self-organize into repeating spatial patterns, i.e., Turing patterns, with no template or specific interparticle interactions. Spots, strings and labyrinth patterns that closely resembled Turing skin pigmentation patterns on various animals were obtained by tuning the chemistry of the system. A series of systematic experiments identified that hydroxyl radicals and NPs as critical species driving the formation of the NP patterns. We expect this work could be used as a model system in establishing design rules for nanoscale pattern formation by reaction – diffusion instability.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 Data-driven design of MXene aerogels with programmable mechanical performance via active learning and collaborative robots(2022) Shrestha, Snehi; Chen, Po-Yen; Chemical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)There is a solid demand for developing intelligent pressure sensing materials for the next generation of soft machines and robots. The piezoresistive pressure sensor requires a high sensitivity within a specific pressure range and possesses superior mechanical stability. Ti3C2Tx MXene-based aerogels with high electrical conductivities have been demonstrated as promising piezoresistive materials for the fabrication of intelligent pressure sensors for diverse sensing applications, from ultra-low stress vibration detection to irregular object grasping. MXene aerogels' piezoresistive behaviors can easily be tuned by changing the fabrication recipes that affect micro/nanostructures. Although many techniques have been reported for fabricating MXene aerogels for specific detection limits, the influence of the interplaying factors and their effect on the aerogels' structures and mechanical properties are not clearly understood. To achieve the custom design for pressure sensors for any given sensing windows and mechanical requirements, understanding the complex correlations between fabrication recipes, aerogel microstructures, and mechanical properties becomes necessary. Since traditional trial-and-error approaches require the production and manual processing of a large amount of data and, therefore, are highly time-consuming. Also, it is impossible to use a trial-and-error-based approach to study multi-dimensional design space as the one needed to construct an enormous amount of MXene-based aerogel sensors. Machine learning is a powerful and versatile tool that uses data-driven computation to uncover underlying trends and complex correlations. Machine learning requires a data-rich system to study the correlations and make accurate analyses and predictions. As the quality and size of the data obtained from the literature remain narrow and biased, it becomes essential to design high-throughput experiments to supply high-quality data to develop prediction models via machine learning. In this presentation, we adopt a hybrid strategy using wet-lab experiments, a machine learning framework, and collaborative robot assistance to build up a prediction model and uncover the underlying design principles to understand the mechanical properties of MXene-based aerogel sensors. Three functional materials (i.e., Ti3C2Tx MXene nanosheets, cellulose nanofibers, and gelatin), and one crosslinker (i.e., glutaraldehyde), are used for the fabrication of piezoresistive aerogels. First, a support-vector machine classifier is trained with 264 different compositions to confirm a feasible fabrication regime. Second, 160 piezoresistive aerogels with various recipes and morphologies are fabricated through active learning loops. Third, through data analyses, data-driven design principles for piezoresistive aerogels were uncovered and validated via in situ microscopic studies. Through this study, we make a crucial discovery about the roles of mass loading and cellulose nanofiber concentration on the mechanical properties of the resulting aerogels. Finally, we demonstrate how the implementation of collaborative robots can accelerate the prediction model construction.Item DYNAMIC ELECTRICAL RESPONSE AT THE NANOSCALE IN METAL HALIDE PEROVSKITES(2022) Lahoti, Richa; Kofinas, Peter; Leite, Marina S; Chemical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Photovoltaic (PV) technology holds a promise that can change the energy dynamics globally. Next-generation materials, with the focus on two factors: high efficiency and economic feasibility, are being extensively explored to enable the widespread implementation of solar cells. Metal halide perovskites (MHPs) provide the ideal combination of both these pressing factors, and also fall under thin-film technology making their applications increasingly ubiquitous. In little over a decade, perovskites have reached a power conversion efficiencies of > 25%. Despite the prodigious advancements in efficiency, device and material instabilities have precluded their commercialization. While the origin of instabilities is multifaceted, instability under environmental factors (light, humidity, oxygen, temperature) is a central hub. Therefore, efforts are being directed toward understanding the behavior of photovoltaic properties under environmental conditions. Investigation at the material level is necessary to develop optimization strategies. My dissertation focuses on the electrical dynamics at length scales of grains and grain boundaries in MHP thin films. In the first part of my thesis, I present a comprehensive electrical analysis by probing surface voltage and photocurrent on Cs-containing dual-cation and Rb-containing quad-cation perovskite thin films. I measure surface voltage response using Kelvin probe force microscopy (KPFM) and map photocurrent via photoconductive atomic force microscopy (pc-AFM) under an inert environment. The Dark KPFM voltage maps indicate upward band bending at the grain boundaries for both chemical compositions. Using an illumination cycle (OFF-ON-OFF), I find a 55% larger post-illumination residual voltage drop in quad-cation perovskite. Photocurrent maps reveal highly photo-active grain boundaries in the quad-cation, while photo-inactivity is observed at grain boundaries in dual-cation perovskite. With the integrated knowledge about the upward band bending from KPFM and the electrical nature of the grain boundaries in the two chemical compositions, I infer defect passivation at the grain boundaries due to Rb+ cations and defect-assisted recombination at the grain boundaries of dual-cation perovskites. The highly conductive grain boundary network seen in quad-cation perovskite increases the overall photocurrent by 50%. The second part of my thesis demonstrates, for the first time, the ability of in situ humidity-dependent KPFM measurements to capture localized moisture-induced electrical dynamics in MHPs. I perform a controlled humidity cycle from 5 - 65% rH and back down from 65 - 5% rH. I observe an enhanced voltage response up to 45% relative humidity and an electrical failure at 65% rH. I capture a self-recovery value of over 90% post-humidity cycle and a recovery value of 99% 24 hours post-humidity cycle. Using XPS and PL before and after the humidity cycle, I confirm moisture-induced structural and chemical changes at the surface of the perovskite which are interconnected to the unstable electrical behavior seen during the humidity cycle. My comprehensive analytical approach on KPFM, and pc-AFM together with my in situ results showcase powerful methods for perovskite stability investigations.Item DETERMINING ELONGATION AT BREAK OF CABLE INSULATIONS USING CONDITION MONITORING PARAMETERS(2022) Gharazi, Salimeh; Al-Sheikhly, Mohamad; Chemical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Many United States nuclear power plants are seeking to renew life licenses to extend the operational life of the plant to an additional 20 or 40 years. Degradation of insulation and jacket of cables, which are originally designed for 40 years in the second round of operation, is a critical issue which can impair the safe and reliable function of cables and ultimately the plant. The main criterion for assessing the end of life of these insulations is defined when the elongation at break reaches 50% of its original value. However, measuring the elongation at break is done by tensile tests, which are destructive and need large samples; the feasibility of these tests is significantly limited on installed cables at nuclear power plants. A new model was developed to relate the changes in the activation energy corresponding to EAB in terms of the changes in the activation energies corresponding to non-destructive condition monitoring, NDE-CM, parameters. The coefficients of the model are obtained by normalizing the calculated activation energy of each CM parameter’s changes with the activation energy of EAB changes. Therefore, it is possible to estimate EAB values, in the present developed equations, from the substitution of activation energy corresponding to EAB changes with the correlated activation energy of the non-destructive condition monitoring parameters. Cable Polymer Aging database, C-PAD, which is provided by Electric Power Research Institute, and supported by the U.S. Department of Energy, along with experimental results done in the University of Maryland, UMD, laboratory was used as the database. While taking advantage of C-PAD database which contains condition monitoring parameters of insulation cables such as Elongation at break, Modulus and Density provided by many U.S. and international research institutes, extensive aging experimental results on two cables, each with two grades provided us with not only a database but also a better understanding of the aging mechanism. The published experimental results of cable insulations are used to validate the model. A good fit between the experimental and modeled results confirms the validity of the model.Item 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.Item SYNTHESIS AND CHARACTERIZATION OF ENERGETIC NANOMATERIALS WITH TUNABLE REACTIVITY FOR PROPULSION APPLICATIONS(2020) Kline, Dylan Jacob; Zachariah, Michael R.; Liu, Dongxia; Chemical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Combustion is the world’s leading energy conversion method in which a fuel and oxidizer react and release energy, typically in the form of heat. Energetic materials (propellants, pyrotechnics, and explosives) have combustion reactions that are so fast that they are generally limited by how quickly the fuel and oxidizer can reach each other. Recent research has employed nanomaterials to reduce the distance between reactants to increase energy release rates. This dissertation attempts to uncover and quantify structure-function relationships in energetic nanomaterials by modifying chemical and physical properties of the materials and characterizing the observed changes using new diagnostic tools. This dissertation begins with the development of diagnostic tools that can capture the dynamics of energetic material combustion using a high-speed color camera to measure temperature. This tool has also been modified into a high-speed microscope that allows for spatial and temperature measurements at microscale length (µm) and time (µs) scales. Changes to chemical formula have been explored for energetic nanomaterial systems, though visualization of the reaction dynamics limited detailed results on reaction mechanisms. The first study performed here probed the role of gas generation vs. thermal effects in energy release rate where it was found that combustion inefficiencies from reactive sintering could be mitigated by introducing a gas-generating oxidizer. To explore combustion improvements in the fuel, a metal fuel nanoparticle manufacturing method was explored, though the combustion performance was again limited by reactive sintering. Another effort to reduce reactive sintering with a gas generator proved successful, but also unveiled the importance of different heat transfer mechanisms for propagation. The role of physical architecture on propellant combustion was also investigated to improve efficiency and versatility in solid propellants. It was found that addition of a poor thermal conductor to a propellant mixture increased the propagation rate of the material and this was attributed to the result increase in burning surface area resulting from inhomogeneous heat transfer. Lastly, this dissertation explores a method to remotely ignite materials using microwaves and titanium nanoparticles. This work sets the stage for a remotely staged solid propellant architecture that would provide control over solid propellant combustion in-operando.