Materials Science & Engineering
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Item INTERFACE AND STRUCTURES IN LITHIUM-GARNET QUASI-SOLID-STATE BATTERIES(2024) Gritton, Jack Evans; Wachsman, Eric D; Material Science and Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)A confluence of adoption of the internet of things, mobile electronics, electric vehicles, and shift towards adoption of intermittent green energy sources has led to a need for rapid improvement in battery technology in metrics ranging from rate capability and energy density to safety. While significant strides have been made through traditional liquid-based lithium-ion batteries, these oft-conflicting demands require fundamental shifts in battery chemistry, especially enabling safe incorporation of lithium metal anodes. Given their high conductivity, non-flammability, wide electrochemical stability window, and stability to lithium metal, lithium-stuffed garnets of the family LLZO provide one of the most promising alternative electrolytes to replace traditional flammable electrolytes. Two of the largest factors holding back these ceramic electrolytes are interfacial compatibilities and the interplay between processing and electrolyte mass. While drastic improvements have been made in the interface between garnet and lithium metal to improve rate capability, similar jumps in full cells have not been observed for rate and capacity. Using a varied cathode loading and a combination of EIS and DRT, we showed that garnet-catholyte interface was the main contributor to resistance in quasi-solid-state batteries of reasonable cathode loadings utilizing Pyr14TFSI based catholyte. Two methods were then used to improve this interface: modification of the garnet structure interfacing with catholyte, and modification of catholyte composition. Through the use of these methods, rate capabilities and capacity were drastically improved from the baseline system, both at elevated and room temperature. In addition to reducing interfacial resistance, cell polarization can be reduced through using thinner electrolytes. Given its higher mass density and lower conductivity in comparison to liquid electrolytes, garnet has historically had to rely on its greater stability to higher energy density electrodes to maintain competitive energy densities or utilize thin-film procedures that reduce mass but result in orders of magnitude lower conductivity than bulk produced garnets. To balance conductivity, ease of processing, and cell mass, a new combination of bulk-derived processing has been developed that allows for thin free-standing cubic garnet and thin, flexible, porous garnet. Cells using these new thin garnets achieved high cycling rates, and significant capacities.Item DEVELOPMENT OF LI+ AND NA+ CONDUCTING CERAMICS AND CERAMIC STRUCTURES FOR USE IN SOLID STATE BATTERIES(2016) Hitz, Gregory; Wachsman, Eric D; Material Science and Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)A solid state lithium metal battery based on a lithium garnet material was developed, constructed and tested. Specifically, a porous-dense-porous trilayer structure was fabricated by tape casting, a roll-to-roll technique conducive to high volume manufacturing. The high density and thin center layer (< 20 μm) effectively blocks dendrites even over hundreds of cycles. The microstructured porous layers, serving as electrode supports, are demonstrated to increase the interfacial surface area available to the electrodes and increase cathode loading. Reproducibility of flat, well sintered ceramics was achieved with consistent powderbed lattice parameter and ball milling of powderbed. Together, the resistance of the LLCZN trilayer was measured at an average of 7.6 ohm-cm2 in a symmetric lithium cell, significantly lower than any other reported literature results. Building on these results, a full cell with a lithium metal anode, LLCZN trilayer electrolyte, and LiCoO2 cathode was cycled 100 cycles without decay and an average ASR of 117 ohm-cm2. After cycling, the cell was held at open circuit for 24 hours without any voltage fade, demonstrating the absence of a dendrite or short-circuit of any type. Cost calculations guided the optimization of a trilayer structure predicted that resulting cells will be highly competitive in the marketplace as intrinsically safe lithium batteries with energy densities greater than 300 Wh/kg and 1000 Wh/L for under $100/kWh. Also in the pursuit of solid state batteries, an improved Na+ superionic conductor (NASICON) composition, Na3Zr2Si2PO12, was developed with a conductivity of 1.9x10-3 S/cm. New super-lithiated lithium garnet compositions, Li7.06La3Zr1.94Y0.06O12 and Li7.16La3Zr1.84Y0.16O12, were developed and studied revealing insights about the mechanisms of conductivity in lithium garnets.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.