Materials Science & Engineering

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    Insulating Materials for an Extreme Environment in a Supersonically Rotating Fusion Plasma
    (2024) Schwartz, Nick Raoul; Koeth, Timothy W; Material Science and Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    Fusion energy has long been sought as the “holy grail” of energy sources. One of the most critical remaining challenges in fusion is that of plasma-facing materials, even denoted by the National Academies of Science. The materials challenge is particularly acute for centrifugal mirrors, an alternative concept to the industry-standard tokamak that may offer a more efficient scheme with a faster path to development. The centrifugal mirror incorporates supersonic rotation into a conventional magnetic mirror scheme, providing three primary benefits: (1) increased confinement, (2) suppression of instabilities, and (3) plasma heating through shear flow. However, this rotation, which is driven by an axial magnetic field and a radial electric field, requires the magnetic field lines to terminate on electrically insulating surfaces to avoid “shorting” the plasma. This unique requirement presents a novel materials challenge: the insulator must not only resist irradiation and thermal damage, but also be an excellent electrical insulator and thermal conductor that can be actively cooled. To address this materials challenge, the Centrifugal Mirror Fusion Experiment (CMFX) was developed at the University of Maryland. CMFX serves as a test bed for electrically insulating materials in a fusion environment, as well as a proof-of-concept for the centrifugal mirror scheme. To guide the design of future power plants and better understand the neutronand ion flux on the insulators, a zero-dimensional (0-D) scoping tool, called MCTrans++, was developed. This software, discussed in Chapter 2, demonstrates the ability to rapidly model experimental parameter sets in CMFX and predict the scaling to larger devices, informing material selection and design. Assuming the engineering challenges have been met, the centrifugal mirror has been demonstrated as a promising scheme for electricity production via fusion energy. One of the key aspects to the operation of CMFX is the high voltage system. This system, discussed in Chapter 3, was developed in incremental stages, beginning with a 20 kV, then 50 kV pulsed power configuration, and finally culminating in a 100 kV direct current power supply to drive rotation at much higher voltages, creating an extreme environment for materials testing. This work identified hexagonal boron nitride (hBN) as a promising insulator material. Computational modeling (Chapter 4) demonstrated hBN’s superior resistance to ion-irradiation damage compared to other plasma-facing materials. Additionally, fusion neutrons are crucial for assessing both material damage and power output. Chapter 5 details the neutronics for CMFX, including 3He proportional counters, which have been installed on CMFX to measure neutron production. In parallel, Monte Carlo computational methods were used to predict neutron transport and material damage in the experiment. Ultimately, a materials test stand was installed on CMFX to expose electrically insulating materials to high energy fusion plasmas (Chapter 6). Comparative analysis of hBN and silicon carbide after exposure revealed superior performance of hBN as a plasma-facing material. Two primary erosion mechanisms were identified by surface morphology and roughness measurements: grain ejection and sputtering, both more pronounced in silicon carbide. This work advances our understanding of insulating material behavior in fusion environments and paves the way for the development of the next-generation centrifugal mirror fusion reactors. Chapter 7 discusses conclusions and proposes future work. In particular this section suggests some changes that may allow CMFX to operate at much higher voltages, unlocking higher plasma density and temperature regimes for further material testing.
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    INTERFACES IN THIN-FILM SOLID-STATE BATTERIES
    (2024) Castagna Ferrari, Victoria; Rubloff, Gary GWR; Material Science and Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    The lack of a diagnostics approach to monitor interface kinetics in solid-state batteries (SSBs) results in an incomplete knowledge of the mechanisms affecting device performance. In this study, a new protocol for process control of SSB interface formation and their evolution during operation is presented. Thin-film SSBs and diagnostic test devices that are composed by a permutation of isolated layers were simultaneously fabricated using sequential sputtering deposition and in-situ patterning using shadow masks. Physics-based electric circuit models were designed for deconvolution of impedance profiles, which enabled an evaluation of bulk properties and space-charge layers at interfaces individually and during operation under different states-of-charge. Relative permittivity values of fundamental battery components (cathode, electrolyte and anode) were calculated as a function of the frequency and the applied voltage. Interfacial impedances, as well as space-charge layers formed at heterojunctions during charge and discharge processes, were successfully deconvoluted using the diagnostic test devices and electric circuit modeling. The cathode-electrolyte interphase was kinetically stable under a voltage window of 0 – 3.6 V vs Cu, and it had an estimated ionic conductivity of the order of 10-9 S/cm, hence it is a localized limiting factor for Li+ transfer. The anode-electrolyte interphase was thermodynamically stable upon completion of the fabrication process, but it became kinetically unstable during charge and discharge cycles. Hence, the proposed diagnostics protocol enlightened the necessity of implementing interfacial engineering on these interphases in the future for improvement of cyclability and stability of SSBs and ionic devices.
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    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.
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    ELECTROLYTE AND INTERFACE DESIGNATION FOR HIGH-PERFORMANCE SOLID-STATE LITHIUM METAL BATTERIES
    (2024) Zhang, Weiran; Wang, Chunsheng; Material Science and Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    The demand for advanced battery technology is intensifying as electric energy becomes the foundation of modern technologies, such as smart devices, transportation, and artificial intelligence. Batteries play a crucial role in meeting our increasing energy demands and transitioning towards cleaner and more sustainable energy sources. However, range anxiety and safety concerns still hinder the widespread application of battery technology.Current Li-ion batteries, based on graphite anode, have revolutionized battery technology but are nearing the energy density limits. This necessitates the development of metal batteries, employing lithium metal as anode which eliminates host materials that do not contribute to capacity, thereby offering 10 times higher specific capacity. Recent research on lithium metal batteries has seen a significant surge, with growing knowledge transitioning from Li+ intercalation chemistry (graphite) to Li metal plating/stripping. The electrolyte, which was previously regarded as an inert material and acting as a Li+ ion transportation mediator, has gradually attracted researchers’ attention due to its significant impact on the solid electrolyte interphase (SEI) and the Li metal plating/stripping behaviors. Compared to the traditional liquid electrolytes, solid-state lithium metal batteries (SSLMB) have been regarded as the holy grail, the future of electric vehicles (EVs), due to their high safety and potential for higher energy density. However, there are notable knowledge gaps between liquid electrolytes and solid-state electrolytes (SSEs). The transition from liquid-solid contact to solid-solid contact poses new challenges to the SSLMB. As a result, the development of SSLMB is strongly hindered by interface challenges, including not only the Li/SSE interfaces and SSE/cathode interfaces but also SSE/SSE interfaces. In this dissertation, I detailed our efforts to highlight the role of electrolytes and interfaces and establish our understanding and fundamental criteria for them. Building on this understanding, we propose effective and facile engineering solutions that significantly enhance batterie metrics to meet real-world application demand. Rather than simply introducing new compositions or new designations, we are dedicated to introducing our understanding and mechanism behind it, we hope the scientific understanding, the practical solution, and the applicability to various systems can further guide and inspire the electrolyte and interface designation for next-generation battery technology.
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    HIGH-ENERGY-DENSITY LITHIUM-SULFUR BATTERIES USING GARNET SOLID ELECTROLYTE: PERFORMANCE AND CHARACTERIZATION
    (2023) Shi, Changmin; Wachsman, Eric EW; Material Science and Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    There is every-growing clean energy storage systems demand to address the climate change challenges. The Lithium-Sulfur (Li-S) battery using solid-state electrolyte (SSE), therefore, are becoming a rising star to meet this requirement due to the low cost and high domestic availability of sulfur, exceptionally high theoretical energy density of sulfur chemistry, less flammability, the potential for suppression of the polysulfide shuttle, Li dendrite growth, low coulombic efficiency, and short circuiting in more conventional liquid electrolyte Li-S batteries. The most popular SSEs in Li-S battery field are Li10GeP2S12 (LGPS) and Li stuffed garnet type Li7La3Zr2O12 (LLZO) with a space group of Ia3 ̅d. LGPS has a high ionic conductivity of 1–10 mS/cm at room temperature (22℃), but the generation of H2S toxic gas when reacting with moisture and the instability with Li metal limit its applications. LLZO is a highly promising SSE for Li-S batteries due to its reasonably high ionic conductivity (0.1–1 mS/cm) at 22℃ and excellent chemical stability with Li metal. However, Li dendrite growth is still observed in LLZO. To overcome the potential Li dendrite growth issue, our group introduced a novel 3D porous/dense bilayer and porous/dense/porous trilayer LLZO structures that achieve an exceptional Li stripping/plating performance at a high current density of 10 mA/cm2 at 22℃ with no applied pressure. Although significant improvement has been done in mitigating the LLZO/Li anode interface, further work on stabilizing the sulfur/LLZO interface still needs to be done to achieve high energy density and stable cycling Li-S batteries. Through the studies in this dissertation, it was observed that La segregation to the LLZO surface on the sulfur cathode side led to Li-S battery charge failure. To address the issue, a PEO-based interlayer was applied on the cathode side to physically separate sulfur cathode and LLZO. Consequently, the Li-S batteries demonstrated a high initial discharge capacity of 1307 mAh/g at 22℃, corresponding to an energy density of 134 Wh/kg and 639 Wh/L. Next, since the PEO-based interlayer has a low ionic conductivity, an in-situ formed gel polymer electrolyte (GPE) was invented as a catholyte that had a high ionic conductivity of 3.5–5.6 mS/cm at 22℃. With an organic sulfur cathode (active material: sulfurized polyacrylonitrile) and a thin bilayer LLZO architecture, a very stable cycling using high sulfur loading (5.2 mg/cm2) was obtained for 60 cycles at a discharge current density of 0.87 mA/cm2 with a high initial discharge capacity of 1542 mAh/g, corresponding to an energy density of 223 Wh/kg and 769 Wh/L. In addition, using the same configuration and sulfur loading but using a different cell, 80% capacity retention for over 265 cycles was demonstrated at a discharge current density of 1.74 mA/cm2 at 22℃. In the third project, as a small amount of flammable organic liquid catholyte and/or GPE compromises on the safety of solid-state batteries, the proof-of-concept “all-solid-state” Li-S battery using LLZO electrolyte was first innovated through a novel three-phase sulfur cathode to meet the high safety demand of solid-state Li-S batteries. In addition, by using the same “all-solid-state” battery design and a 3D column LLZO architecture, a high energy density of 338 Wh/kg and 797 Wh/L was demonstrated.
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    ELECTROCHEM-MECHANICS CHARACTERIZATION OF SI ELECTRODE/SI BASED SOLID-STATE BATTERY
    (2022) Wang, Haotian; Rubloff, Gary; Material Science and Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    Li-ion battery (LIB) is a popular energy storage device that predominates the market of microelectronics due to its high energy density and light weight. In the recent trend of electrification of vehicles, LIBs also showed promise in the application of electric vehicles but the energy density of current LIBs with graphite electrode doesn’t suffice the need of long driving range. Replacing graphite electrode with alloying type electrodes that have almost ten times higher energy density is thus a necessary route to improve the energy density of LIBs. However, alloying type electrodes, such as Si and Sn, typical undergo enormous volume change (up to 310%) during Li insertion and extraction, which lead to various mechanical problems such as cracking, delamination, and pulverization. These mechanical issues eventually cause catastrophic capacity fading in LIBs and thus, are central topics for the application of alloying type electrodes in next generation LIBs. This dissertation presents a three-phase experimental study of stress development in Si electrodes and Si based solid state batteries. In the first phase, ex-situ stress characterization in single-c Si electrode was performed to validate Raman spectroscopy as a promising stress characterization technique for Si electrode. In the second phase, in-situ stress characterization in patterned poly-c Si electrode with confocal micro-Raman setup was performed, to investigate the correlation between complex geometries and stress distribution in crystalline Si electrode and the critical size effect. In the last phase, a solid-state battery (SSB) platform device with lateral layout was proposed and validated for stress characterization in Si based SSBs. The platform device can also serve as a versatile testbed for electrochemistry study of bulk SSB components and interfaces. Overall, this dissertation demonstrates a methodology that combines Raman spectroscopy, novel design of electrochemical devices, and computational modeling as a powerful tool for electrochemo-mechanics study of alloying type electrodes and SSB systems.
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    Examination of a Highly Porous Gel Polymer Interlayer for Interfacial Improvement in Solid State Lithium Batteries
    (2022) Rae, Tyler Jeffrey; Wachsman, Eric; Material Science and Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    Solid-state lithium garnet (LLZT) electrolytes display relatively high ionic conductivity, thermal stability, and compatibility with lithium metal, which makes them encouraging for the future of lithium-ion batteries. As with many other solid electrolytes, their main weakness is poor contact and high interfacial resistance with electrodes. The use of polymer gels as interlayers has been demonstrated to reduce this interface, improving cell stability and lifespan. In this study, immersion precipitation has been explored as a preparation method to create poly(vinylidene fluoride)-co-hexafluoropropylene (PVDF-HFP) polymer membranes. The resultant microstructure is highly porous and can uptake nearly 600% its weight in liquid electrolyte when forming a gel. Polymethyl methacrylate (PMMA) and lithium fluoride (LiF) are incorporated into the membranes and evaluated for their contributions to mechanical and electrochemical properties. Membranes containing LiF showed high stability up to 4.5 V vs Li/Li+ and were analyzed in cells of composition NMC/PVDF-HFP/LLZT/Li. Specific discharge capacities up to 174 mAh/g were achieved during early cycling and showed promise for future exploration and application in quasi-solid-state lithium-ion batteries.
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    Ultrathin Materials for Advanced Energy Storage
    (2020) Hitz, Emily Michelle; Hu, Liangbing; Rubloff, Gary W; Material Science and Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    The demand for batteries that can meet the high energy density and reliability needs of the future is ever growing and drives current research trends in the battery field toward the development of practical metallic Li anodes. Overcoming the difficult rechargeability and safety obstacles that affected the first-generation lithium-ion batteries in decades past has required diligent research and introduced of a host of new material systems, including solid-state inorganic electrolytes. Solid-state electrolytes represent a fundamental departure from conventional liquid-electrolyte lithium-ion batteries and offer a path toward versatile and high-energy-density energy storage. Inorganic solid-state electrolytes have still faced challenges, such as unfavorable interface characteristics with electrode materials and low ionic conductivity compared to liquid electrolytes, but recent advancements have helped to overcome these obstacles and position solid-state electrolytes as promising candidates for use in state-of-the-art batteries. To achieve widespread adoption of solid-state electrolytes, however, prevailing issues like Li dendrite formation and subsequent electrical shorting must be understood and solved. Based on research that suggests a dependence of dendrite formation on the electronic conductivity of garnet-type Li6.75La3Zr1.75Ta0.25O12 (LLZO-Ta) solid electrolyte, I first investigate a thin, conformal layer of electronic-insulating, ion-conducting lithium phosphorus oxynitride (LiPON) deposited at the interface between garnet-type electrolyte and a metallic Li alloy anode. Using atomic layer deposition to ensure continuity of the LiPON layer across the garnet LLZO-Ta surface, I fabricate Li-Li symmetric cells that achieve long cycle life free of dendrites. After demonstrating the merits of a thin, electronically insulating layer applied at the interface between Li metal and LLZO-Ta, I probe into the relationship between the ionic and electronic conductivity of solid-state electrolytes with the goal of providing guidance on the rational design of dendrite-free solid-state electrolytes. Toward this aim, I consider an electronic-conductivity-modulated LLZO-Ta electrolyte matrix with LiPON coatings of varying thickness. With support from literature, I also explore the implications of an electron-blocking, ion-conducting layer in full-cell batteries, drawing conclusions about their potential use at the cathode-electrolyte interface. The impact of ion-conducting, electron-blocking thin surface coatings for Li dendrite inhibition in solid-state electrolytes is far-reaching and provides a reliable strategy for high-performance solid-state batteries.
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    Performance and Enhancement of Solid Oxide Fuel Cell Electrodes Via Surface Modification
    (2020) Robinson, Ian Alexander; Wachsman, Eric D; Material Science and Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    Solid oxide fuel cells (SOFCs) electrochemically convert chemical fuels to usable electricity with high efficiency and can operate on any oxidizable fuel. SOFCs fuel flexibility is accompanied by clean conversion by only converting the fuel to H2O and CO2 without the production of NOx. Additionally, the design of the device allows for a facile integration of carbon capture because the exhaust from the anode and cathode are already separated, allowing for a separated CO2 stream for carbon capture. Technical limitations have prohibited the commercial deployment of SOFCs at an impactful scale and the SOFC market is currently worth <$1 billion. The high operating temperature (T>800 °C) of SOFCs limits possible applications due to high degradation rates within cell components and a high balance of plant costs to use the requisitespecialized high temperature materials. The primary limitation to using to a lower temperature SOFC is the sluggish kinetics of the air electrode or cathode oxygen reduction reaction (ORR) at lower temperatures. This work increases the activity and durability of SOFC electrodes at lower temperatures by utilizing a facile, effective, low cost surface modification technique, defect engineering, and universal cathode scaffold design. Surface modification of SOFC cathodes also prevents the deactivation of the SOFC cathode typically caused by contaminant gasses like CO2 in Sr0.5Sm0.5CoO3-δ (SSC) cathodes. The surface modification technique also shows breakthroughs in the activity of SOFC cathodes SSC and La1-xSrxCo1-yFeyO3-δ (LSCF), allowing the SOFC to operate below 600 °C. The use of an engineered porous functional layer is shown to reduce the electronic leakage current in ceria-based electrolytes. This type of functional layer also increases the overall performance and durability of a SOFC at lower temperatures. Additionally, an approach was developed to deposit any desired cathode electrocatalyst on a universal scaffold to enable low-temperature operation and is compatible with existing cell components. 1 W/cm2 at 550 °C is achieved by utilizing the scaffold infiltration approach and demonstrates that high performance operations at low temperatures is achievable. Finally, the fuel flexibility of metal-supported solid oxide fuel cells (MS-SOFCs) was demonstrated to highlight their potential applications for carbon neutral transportation.
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    RADIATION SYNTHESIS OF IONIC LIQUID POLYMER ELECTROLYTE MEMBRANE FOR HIGH TEMPERATURE FUEL CELL APPLICATIONS
    (2020) Mecadon, Kevin; Al-Sheikhly, Mohamad; Material Science and Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    The purpose of this thesis was to design, synthesize and analyze innovative anhydrous fuel cell membranes that can operate at temperatures above 100°C. Operating at this higher temperature region improves performance and reliability of fuel cells: increasing proton mobility, enhancing reaction kinetics, increasing catalysis activity and reducing carbon monoxide poisoning. Traditional polymer electrolyte membrane fuel cells (PEMFCs) do not operate efficiently above 100°C because water is used as a proton conductive medium though the Grotthuss hopping mechanism. Through substituting water with protic ionic liquids and grafting onto fluorocarbon films, a new proton conductive network solid state PEM has been developed. These membranes can perform at high temperature above 100°C. Polymers were selected for grafting based on the following properties: high proton conductivity, low electrical conductivity, high mechanical properties, high chemical resistance, and high temperature and humidity stability. The method used to synthesize these anhydrous polymer electrolyte membranes (PEMs) was radiation grafting using heterocyclic protic ionic liquid monomers and fluorocarbon substrates. PEMs were prepared at the Medical Industrial Radiation Facilities (MIRF) at the National Institute of Standards and Technology (NIST). MIRF is a 10.5 MeV electron beam accelerator, which was used to radiate the fluorocarbon substrate and then indirectly graft heterocyclic protic ionic liquids to create PEMs. After synthesis, the extent and uniformity of PEM composition was analyzed using FTIR microscopy, SEM/EDS, SANS and their proton conductivity as measured by EIS. Through this research, indirect radiation grafting was shown to covalently bond ionic liquids onto fluorocarbon substrates to synthesize PEMs. The resulting ionic liquid PEMs showed proton conductivities greater than 10-3 S/cm above 100°C that behaved independent of humidity. The ionic liquid PEMs also demonstrated a positive correlation of increasing proton conductivity with increasing temperatures above 100°C even after the PEMs are dehydrated. The chemical properties and structure of the grafted ionic liquids greatly affects the proton conductive mechanisms present in the PEMs. These trends found through the course of this research will help the development of future anhydrous PEM with higher proton conductivity, performance, and reliability.