Theses and Dissertations from UMD
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Item DIRECT INK WRITING SOLID-STATE LI+ CONDUCTING CERAMICS FOR NEXT GENERATION LITHIUM METAL BATTERIES(2024) Godbey, Griffin Luh; Wachsman, Eric D; Material Science and Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The global pursuit of safer and higher-capacity energy storage devices emphasizes the crucial link between the microstructures of electrochemically active materials and overall battery performance. The emergence of solid-state electrolytes featuring multi-layered, variable porosity microstructures presents fresh opportunities for developing the next generation of rechargeable batteries. However, this advancement also brings forth novel challenges in terms of device integration and operation. In this dissertation, solid-state Li-ion conducting electrolytes were 3D printed to enhance the performance of porous electrolyte layers within porous-dense-porous trilayer systems.LLZO-based garnet electrolyte scaffolds were fabricated via 3D printing using direct ink writing (DIW), facilitating the generation of scaffolds with minimal tortuosity and constriction in comparison to previous porous scaffolds manufactured through tape casting. Rheological techniques, including stress and time sweep tests, were employed to characterize the DIW inks and discern their conformal and self-supporting properties. The analysis focused on ink characteristics critical for Direct Ink Writing (DIW), emphasizing properties essential for achieving high aspect ratio printing and minimal constriction in 3D structures. Drawing from this ink research, two distinct 3D architectures, columns and grids, were fabricated. Column structures were utilized in assembling Li-NMC622 and Li-SPAN cells, with detailed discussions highlighting improvements in printing and sintering outcomes. Notably, NMC622, characterized by larger particle sizes, demonstrated complete infiltration within 3D printed porous networks, yielding a promising specific capacity of 169.9 mAh/g with minimal capacity fade. Further optimization involved integrating a porous 3D scaffold to facilitate SPAN infiltration in Li-SPAN cells, resulting in a specific capacity of 1594 mAh/g, albeit with significant capacity fade. The Li-S was implemented into a grid structure achieving 763 mAh/gS with less than 0.25% capacity loss over 16 cycles. Lastly, comprehensive morphology analysis was conducted to evaluate the effectiveness of our optimal DIW structures and to inform future enhancements of such cells.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 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 ELECTROCHEMICAL PROTECTION OF LITHIUM METAL ANODE IN LITHIUM-SULFUR BATTERIES AND BEYOND(2020) Wang, Yang; Lee, Sang Bok; Chemistry; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)With the growing demand of advanced energy storage devices that have high energy density and high power density to power electric vehicles and electrical grid, scientists and engineers are exploring technologies beyond conventional Li-ion batteries which have transformed the industry in the past thirty years. Li-S batteries have much higher energy density than Li-ion batteries and are gaining momentum. However, the intrinsic issues of Li-S batteries require a comprehensive systematic study of the protection of Li metal anodes to put them into practical applications. In the first study of this dissertation, we investigated using conventional electrolyte of Li-S batteries that includes 1,3-dioxolane to electrochemically pretreat Li metal anodes. We concluded that the electrochemical pretreatment of Li metal anodes generated an organic-inorganic artificial solid electrolyte interface (ASEI) layer that greatly enhanced the battery performance of the Li-S batteries. The properties of this ASEI can be tuned by manipulating the current density and cycle number of the electrochemical pretreatment. In the second study, we studied the comprehensive development and surface protection of Li10GeP2S12 (LGPS) material as solid-state electrolyte, which has ionic conductivity comparable to liquid electrolytes, potentially for solid-state Li-S batteries. Lithium phosphorus oxynitride (LiPON) was coated onto LGPS pellets by atomic layer deposition (ALD). It demonstrated great compatibility with LGPS and extends the electrochemical stability window. The third study explored the potential of transferring this electrochemical pretreatment method to the protection of other metal anodes, particularly Mg. The study discovered the surprising catalytic capability of Mg2+ in the polymerization of solvent 1,3-dioxolane (DOL). A layer with poly-DOL component was also found to grow on the surface of Mg metal anodes as a result of the electrochemical pretreatment, and the overpotential of Mg-Mg symmetric cells cycling dropped with the growth of the layer. Future studies are required to test the effectiveness of this method in Mg batteries. Overall, these studies can help to understand the surface chemistry of the electrochemically pretreated Li metal anodes, provide guidelines on the improvement of Li-S batteries and contribute to the development of solid-state Li-S batteries and multivalent metal anode batteries.Item ELECTROCHEMISTRY OF PRECISION NANOSTRUCTURES FOR HIGH PERFORMANCE ENERGY STORAGE DEVICES(2020) Kim, Nam; Lee, Sang Bok; Chemistry; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)With the increase in the demand for high performing energy storage devices, the energy storage community has explored ways to improve Li-ion battery chemistry. Previous research has demonstrated that nanostructuring of Li-ion electrodes enables significant improvements in their power and energy densities. However, a systematic study is needed to quantify the impact of specific structural properties on the electrochemical behavior of the nanostructured electrode and to develop a guideline for high performance energy storage devices. In the first study of this dissertation, we investigate the impact of pore diameter, dynamic conductivity and interconnected structures on the electrochemistry of V2O5, cathode material for Li ion batteries. We determined that there were positive and negative effects of the interconnected structure depending on the material properties. When V2O5’s electronic conductivity increased with the degree of lithiation, a higher power density was measured with more interconnections. When the material’s electronic conductivity decreased with lithiation, a lower power density was measured with more interconnections. In the second study, we employ microfabrication techniques and atomic layer deposition to fabricate well defined nanochannels to study the effect of electrolyte nanoconfinement on the electrochemistry of anatase TiO2. Surprisingly, nanoconfinement resulted in high energy and power densities when compared to the bulk material. Simulations showed that the improvement in the electrode behavior was due to the negative surface charges of TiO2 which resulted high local concentration of Li ions within the nanochannel and minimal loss in the driving potential was observed at the stern layer. In the third study, we fabricate a platform for high performance 3D solid state batteries on a Si wafer to study the effect of high aspect ratio nanostructures on the electrochemical behavior of thin film solid state batteries. The V2O5 electrode in 3D scaffold showed 113 times higher capacity than the planar electrode at 2μA/cm2 and 1333 times higher capacity at 0.5mA/cm2. These studies can help to understand key structural parameters for improved Li-ion batteries, and the test platforms we developed in these studies can be applied to increase understanding of structural impacts on other ion battery chemistries as well.Item Nanomaterials for Garnet Based Solid State Energy Storage(2018) Dai, Jiaqi; Hu, Liangbing; Material Science and Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Solid state energy storage devices with solid state electrolytes (SSEs) can potentially address Li dendrite-dominated issues, enabling the application of metallic lithium anodes to achieve high energy density with improved safety. In the past several decades, many outstanding SSE materials (including conductive oxides, phosphates, hydrides, halides, sulfides, and polymer-based composites) have been developed for solid-state batteries. Among various SSEs, garnet-type Li7La3Zr2O12 (LLZO) is one of the most important and appealing candidates for its high ionic conductivity (10-4~10-3 S/cm) at room temperature, wide voltage window (0.0-6.0V), and exceptional chemical stability against Li metal. However, its applications in current solid state energy storage devices are still facing various critical challenges. Therefore, in this quadripartite thesis I focus on developing nanomaterials and corresponding processing techniques to improve the comprehensive performance of solid state batteries from the perspectives of electrolyte design, interface engineering, cathode improvement, and full cell construction. The first part of the thesis provides two novel designs of garnet-based SSE with outstanding performance enabled by engineered nanostructures: a 3D garnet nanofiber network and a multi-level aligned garnet nanostructure. The second part of the thesis focuses on negating the anode|electrolyte interfacial impedance. It consists of several processing techniques and a comprehensive understanding, through systematic experimental analysis, of the governing factors for the interfacial impedance in solid state batteries using metallic anodes. The third part of the thesis reports several processing techniques that can raise the working voltage of Li2FeMn3O8 (LFMO) cathodes and enable the self-formation of a core-shell structure on the cathode to achieve higher ionic conductivity and better electrochemical stability. The development and characterization of a solid state energy storage device with a battery-capacitor hybrid design is included in the last part of the thesis.Item Scheduling in Energy Harvesting Systems with Hybrid Energy Storage(2013) Shahzad, Khurram; Ulukus, Sennur; Electrical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)In wireless networks, efficient energy storage and utilization plays a vital role, resulting in a prolonged lifetime and enhanced throughput. This factor becomes even more important in systems employing energy harvesting as compared to utility or battery powered networks, where a constant supply of energy is available. Therefore, it is crucial to design schemes that make the best use of available energy resources, keeping in view the practical constraints. In this work, we consider data transmission with an energy harvesting transmitter which has hybrid energy storage with a perfect super-capacitor (SC) and an inefficient battery. The SC has finite storage space while the battery has unlimited storage space. The transmitter can choose to store the harvested energy in the SC or in the battery, while draining energy from the SC and the battery simultaneously. Under this energy storage setup, we solve throughput optimal energy allocation problem over a point-to-point channel in an offline setting. The hybrid energy storage model with finite and unlimited storage capacities imposes a generalized set of constraints on the transmission policy. We show that the solution is found by a sequential application of the directional water-filling algorithm. Next, we consider offline throughput maximization in the presence of an additive time-linear processing cost in the transmitter's circuitry. In this case, the transmitter has to additionally decide on the portions of the processing cost to be drained from the SC and the battery. Despite this additional complexity, we show that the solution is obtained by a sequential application of a directional glue-pouring algorithm, parallel to the cost-less processing case. Finally, we provide numerical illustrations for optimal policies and performance comparisons with some heuristic online policies.Item Atomic Layer Deposition of Ru and RuO2: New Process Development, Fabrication of Heterostructured Nanoelectrodes, and Applications in Energy Storage(2013) Gregorczyk, Keith E.; Rubloff, Gary W; Material Science and Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The ability to fabricate heterostructured nanomaterials with each layer of the structure having some specific function, i.e. energy storage, charge collection, etc., has recently attracted great interest. Of the techniques capable of this type of process, atomic layer deposition (ALD) remains unique due to its monolayer thickness control, extreme conformality, and wide variety of available materials. This work aims at using ALD to fabricate fully integrated heterostructured nanomaterials. To that end, two ALD processes, using a new and novel precursor, bis(2,6,6-trimethyl-cyclohexadienyl)ruthenium, were developed for Ru and RuO2 showing stable growth rates of 0.5 Å/cycle and 0.4 Å/cycle respectively. Both process are discussed and compared to similar processes reported in the literature. The Ru process is shown to have significantly lower nucleation while the RuO2 is the first fully characterized ALD process known. Using the fully developed RuO2 ALD process, thin film batteries were fabricated and tested in standard coin cell configurations. These cells showed high first cycle gravimetric capacities of ~1400 mAh/g, which significantly degraded after ~40 cycles. Rate performance was also studied and showed a decrease in 1st cycle capacity as a function of increased rate. These results represent the first reports of any RuO2 battery studied beyond 3 cycles. To understand the degradation mechanisms witnessed in the thin film studies in-situ TEM experiments were conducted. Single crystal RuO2 nanowires were grown using a vapor transport method. These nanowires were cycled inside a TEM using Li2O as an electrolyte and showed a ~95% volume expansion after lithiation, ~26% of which was irreversible. Furthermore, a chemical irreversibility was also witnessed, where the reaction products Ru and Li2O remain even after full delithiation. With these mechanisms in mind heterostructured nanowires were fabricated in an attempt to improve the cycling performance. Core/shell TiN/RuO2 and MWCNT/RuO2 structures were fabricating using the ALD process developed in this work. While the TiN/RuO2 structures did not show improved cycling performance due to connection issues, the MWCNT/RuO2 structure showed a stable areal capacity of ~600 μAh/cm2 after ~20 cycles and were easily cycled 100 times.