Materials Science & Engineering
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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 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 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.