https://scholarworks.unist.ac.kr/handle/201301/53 Wed, 08 Apr 2026 21:26:33 GMT 2026-04-08T21:26:33Z https://scholarworks.unist.ac.kr/handle/201301/90997 Title: Design of a Deployable Strain-invariant Electromagnetic Wave Absorber Enabled by Magnetic Auxetic Metamaterial Author(s): Jung, Dawoon Abstract: The rapid expansion of high-capacity wireless communication has accelerated the use of millimeter- wave (mmWave) electromagnetic radiation, intensifying concerns over electromagnetic interference (EMI) in emerging electronic systems. In particular, the growing demand for wearable, conformable, and stretchable electronics necessitates broadband EMI absorbers capable of maintaining stable performance under mechanical deformation. However, conventional absorbers exhibit strain-induced degradation of impedance matching and resonant characteristics, posing a significant challenge for mechanically reconfigurable platforms. This dissertation presents a strain-invariant and deployable electromagnetic absorber enabled by a synergistic integration of magnetic materials, auxetic mechanical metamaterials, and electromagnetic metapatterns. The core novelty of this work lies in a co-design strategy in which the auxetic deformation pathway and the meta-pattern geometry are engineered together to suppress absorption degradation during mechanical stretching. The proposed absorber comprises three key design components: (1) a magnetic composite layer providing effective mmWave absorption through controlled complex permeability; (2) a laser-cut auxetic topology that enables large, reversible deployment while regulating in-plane strain distribution; and (3) circular screen-printed silver meta-patterns whose rotational symmetry minimizes strain-dependent variations in effective impedance. To establish the design framework, theoretical analyses based on electromagnetic wave propagation was conducted to identify optimal material parameters, geometric structures, and pattern motifs for strain-invariant absorption. The absorber was fabricated as a 0.45-mm-thick magnetic composite film using a thermoplastic polyurethane matrix, followed by precision laser cutting to introduce the deployable auxetic structure. Circular conductive meta-patterns were subsequently deposited via screen printing to achieve robust electromagnetic behavior under mechanical deformation. The strain-invariant EMI absorption performance was experimentally validated using a millimeter- wave vector network analyzer. The fabricated absorber exhibits a broad absorption bandwidth of 25 GHz (more than 90% absorption), which is preserved up to 20% linear strain (44% areal strain) without noticeable decrease of the absorption bandwidth. Comparative analysis with state-of-the-art absorbers confirms that the proposed design not only achieves superior bandwidth stability under strain but also uniquely provides deployability, enabling compact storage and on-demand expansion—a capability rarely demonstrated in existing mmWave absorption technologies. Major: Department of Materials Science and Engineering Sat, 31 Jan 2026 15:00:00 GMT https://scholarworks.unist.ac.kr/handle/201301/90997 2026-01-31T15:00:00Z https://scholarworks.unist.ac.kr/handle/201301/90996 Title: Preparation of Energy-Storing Current Collectors Based on Si-incorporated Carbon Nanotube Films Author(s): Oh, Eunjae Abstract: The rapid growth of the electric vehicle (EV) industry in recent years has further intensified the demand for high-performance lithium-ion batteries (LIBs), making the improvement of cell energy density an increasingly important challenge in the development of next-generation energy storage technologies.Although most strategies have focused on increasing the capacity of active materials, minimizing the mass of inactive components that do not directly participate in electrochemical reactions has recently emerged as an equally effective approach to improving cell-level energy density. Reducing the inactive mass increases the proportion of active materials in the total electrode weight, thereby enhancing both the gravimetric energy efficiency of the cell. The copper (Cu) foil current collector constitutes a considerable portion of the total electrode weight despite being electrochemically inert. Replacing it with lightweight, conductive, and flexible materials therefore represents a promising route to higher energy density. Carbon nanotubes (CNTs) have attracted increasing attention as next-generation current collectors owing to their excellent electrical conductivity, outstanding mechanical strength, and extremely low density. CNT films fabricated via a direct spinning process possess a highly interconnected fibrous network with tunable alignment and porosity, which enables efficient electron transport and provides a favorable structure for the uniform dispersion and stable incorporation of high-capacity active materials such as silicon (Si). These structural advantages render CNT films excellent candidates for multifunctional electrodes that combine electrical conduction, mechanical reinforcement, and electrochemical activity. Lightweight CNT film current collectors were fabricated by the direct spinning method and subsequently integrated with Si active material to form high-energy-density anodes. The effects of CNT fiber orientation and film density on electrochemical performance were systematically investigated. Morphological and structural characterizations were assessed using field-emission scanning electron microscopy (FE-SEM), and Raman spectroscopy, while electrochemical behaviors were evaluated through galvanostatic charge–discharge tests, cyclic voltammetry (CV), rate capability, and electrochemical impedance spectroscopy (EIS). These analyses elucidated the relationship between the CNT network architecture, charge-transfer pathways, and the resulting energy storage characteristics. The CNT film current collector, featuring both high electrical conductivity and intrinsic electrochemical activity, effectively contributed to charge storage while maintaining mechanical integrity and ultralow density. This combination of properties allows the CNT film to function not only as a conductive scaffold but also as an electrochemically responsive component within the electrode system. The developed CNT-based current collector therefore shows great promise for achieving a remarkable enhancement in cell-level energy density. These findings highlight a practical and scalable design strategy for next-generation lithium-ion batteries and related high-performance energy-storage technologies. Major: Department of Materials Science and Engineering Sat, 31 Jan 2026 15:00:00 GMT https://scholarworks.unist.ac.kr/handle/201301/90996 2026-01-31T15:00:00Z https://scholarworks.unist.ac.kr/handle/201301/90995 Title: Nanoporous Cu dealloyed from intermetallic MgCu2 and its catalytic properties in formaldehyde oxidation reaction Author(s): Yeo, Jiyoon Abstract: Nanoporous Cu (np-Cu) has recently been considered for use in a variety of functional materials, such as catalysts and sensors, due to its advantages such as excellent electrical conductivity, chemical reactivity, and high specific surface area. Furthermore, research has shown that np-Cu can be successfully fabricated using a dealloying method utilizing selective leaching of sacrificial elements in the precursor, which is much simpler than other nanostructuring techniques such as templating or laser etching. However, cracking due to volume shrinkage during the dealloying process is known to negatively impact not only the mechanical properties of np-Cu but also its functional performance. The most intuitive and effective way to suppress cracking during the dealloying process is to reduce the degree of volume shrinkage by lowering the relative proportion of the sacrificial element in the precursor. For example, when applying an Al–Cu alloy precursor to the dealloying process, the relative proportion of the sacrificial element Al must be maintained at 50 at.% or higher to ensure the formation of a nanoporous structure throughout the entire region. However, the authors have discovered that when an intermetallic MgCu2 precursor is applied to dealloying, the relative proportion of Mg, which acts as a sacrificial element, can be reduced to 33 at.%, resulting in significantly reduced cracking induced by volume shrinkage. In this study, the structure and mechanical properties of np-Cu dealloyed from MgCu2 are comparatively investigated with those of np-Cu samples dealloyed from other precursor materials in the literature, and the catalytic properties of the new type of np-Cu in the formaldehyde oxidation reaction (FOR) are also presented to explore its potential for functional applications. Major: Department of Materials Science and Engineering Sat, 31 Jan 2026 15:00:00 GMT https://scholarworks.unist.ac.kr/handle/201301/90995 2026-01-31T15:00:00Z https://scholarworks.unist.ac.kr/handle/201301/88207 Title: Strategic Surface Engineering of Lithium Metal Anodes: Simultaneous Native Layer Elimination and Protective Layer Formation via Gas-Solid Reaction Author(s): Choi, Siwon Abstract: Lithium (Li) metal has received significant attention as an anode material for next-generation batteries due to its high theoretical capacity and low redox potential. However, the high reactivity of Li metal leads to the formation of a native layer on its surface, inducing non-uniform Li+ flux at the electrolyte/Li metal interface, which promotes the growth of Li metal dendrites. In this study, perfluorooctyltriethoxysilane (PFOTES) was vaporized to chemically react with the native layer and modify the Li metal surface. This gas-solid reaction removes the native layer while simultaneously forming a homogeneous solid electrolyte interphase (SEI) layer. The Si–O–Si network formed through condensation reactions between PFOTES molecules, combined with the fluorinated carbon chain of PFOTES, facilitates rapid Li+ kinetics at the Li metal/electrolyte interface. Consequently, the exchange current density of PFOTES-modified Li (PFOTES-Li) increased to 0.2419 mA cm–2, which is 20 times higher than that of Bare-Li (0.0119 mA cm–2). The SEI layer derived from PFOTES effectively mitigates Li pulverization and the formation of dead Li during the long-term cycling. As a result, the PFOTES-Li; LiNi0.8Mn0.1Co0.1O2 full cell exhibits an excellent discharge capacity of 203.4 mAh g−1 under a high areal loading of 4.2 mAh cm–2. This study demonstrates a gas-solid reaction strategy for removing the native layer from the Li metal surface while forming a stable SEI layer, thereby ensuring high Li+ conductivity and mechanical stability, thus improving the cycling stability of Li metal batteries. Major: Department of Materials Science and Engineering Thu, 31 Jul 2025 15:00:00 GMT https://scholarworks.unist.ac.kr/handle/201301/88207 2025-07-31T15:00:00Z