https://scholarworks.unist.ac.kr/handle/201301/119 2026-04-08T22:23:33Z 2026-04-08T22:23:33Z Choi, Tae Young https://scholarworks.unist.ac.kr/handle/201301/91113 2026-03-26T13:16:50Z 2026-01-31T15:00:00Z

Title: Visualizing Correlation between Electrode-Level Heterogeneity and Li Plating in Graphite Anodes via Operando Side-View Optical Microscopy Author(s): Choi, Tae Young Abstract: Reaction heterogeneity at electrode scale plays a critical role in governing the performance, degradation, and safety of lithium-ion batteries, particularly under fast-charging conditions. While lithium plating has traditionally been associated with operating parameters such as C-rate and temperature, its strong coupling with internal reaction heterogeneity arising from electrode architecture remains insufficiently understood. In this work, we systematically investigate electrode-scale reaction heterogeneity using electrode porosity as a key structural parameter and elucidate its direct relationship with lithium plating behavior in graphite anodes. Graphite electrodes with identical areal capacity were fabricated with controlled porosities through systematic calendering, enabling isolation of porosity-induced transport effects. Electrochemical characterization revealed that decreasing porosity intensifies diffusion limitations, leading to increased overpotential, earlier transition to constant-voltage charging, and accelerated capacity fade, particularly under high C-rate operation. Differential capacity (dQ dV⁻¹) analysis demonstrated pronounced peak broadening and suppression of distinct staging transitions with decreasing porosity, indicating increasingly heterogeneous lithiation behavior at the electrode scale. Complementary in situ X-ray diffraction further confirmed the coexistence of multiple graphite intercalation phases in low-porosity electrodes, even at high states of charge, highlighting incomplete and spatially non-uniform phase evolution. To directly visualize reaction heterogeneity, operando optical microscopy was employed as a non- destructive, spatially resolved diagnostic tool. By leveraging lithiation-induced color evolution of graphite and quantitative analysis using the CIELAB color space, depth- and areal-resolved phase distributions were extracted in real time. Porosity 40% electrodes exhibited relatively uniform lithiation across both depth and surface directions, whereas porosity 30% electrodes developed pronounced reaction localization near the electrode surface, which intensified with increasing C-rate. Importantly, lithium plating was preferentially observed in regions exhibiting strong reaction heterogeneity, demonstrating that plating is not solely determined by global operating conditions but is critically governed by localized transport limitations and reaction non-uniformity. By correlating electrochemical signatures, structural evolution, and operando visualization, this study establishes reaction heterogeneity as a key intermediate factor linking electrode design parameters to lithium plating formation. These findings highlight the necessity of heterogeneity-aware electrode design, emphasizing that porosity optimization must balance energy density and transport uniformity to suppress localized current concentration and irreversible lithium deposition. The insights provided herein offer a framework for designing durable, fast-charging-capable lithium-ion battery electrodes through informed control of electrode architecture. Major: School of Energy and Chemical Engineering

2026-01-31T15:00:00Z Seitova, Aizhan https://scholarworks.unist.ac.kr/handle/201301/88248 2025-11-06T00:58:00Z 2025-07-31T15:00:00Z

Title: Engineering of CODH enzyme for increased electron mediator affinity and formate production Author(s): Seitova, Aizhan Major: School of Energy and Chemical Engineering

2025-07-31T15:00:00Z Annageldyyev, Bayrammuhammet https://scholarworks.unist.ac.kr/handle/201301/88247 2025-11-06T00:57:59Z 2025-07-31T15:00:00Z

Title: STUDY OF MESOPOROUS SILICA-TEMPLATED CARBON Author(s): Annageldyyev, Bayrammuhammet Major: School of Energy and Chemical Engineering

2025-07-31T15:00:00Z Shim, Hyunji https://scholarworks.unist.ac.kr/handle/201301/88245 2025-11-06T00:57:58Z 2025-07-31T15:00:00Z

Title: Influence of Polymer Topologies on Curing Mechanism and Recyclability Author(s): Shim, Hyunji Abstract: Polyurethane is widely used in various industries due to its structural strength and chemical resistance, but in particular, thermoset polyurethane has a limitation that it is almost impossible to recycle due to its crosslinked structure. Polyurethanes, despite their widespread industrial applications, present significant recycling challenges due to their thermoset nature. While recent studies have explored dynamic covalent chemistry to improve recyclability, the effect of macromolecular topology on reprocessing behavior remains underexplored. In this study, thermoplastic polyurethanes were synthesized by reacting topology-controlled polyols (branched cyclic, hyperbranched, and linear) with pentamethylene diisocyanate. The resulting polymers were characterized using swelling tests, FT-IR, TGA, and DSC, and their reprocessing behavior was investigated via DMA and UTM. Interestingly, all topologies—branched cyclic, hyperbranched, and linear—exhibited increasing brittleness upon repeated reprocessing. For branched cyclic structures, alternating transitions between intermolecular and intramolecular transcarbamoylation were observed, but their cyclic nature partially suppressed intramolecular cross-linking, resulting in relatively stable mechanical performance over multiple cycles. In contrast, hyperbranched and linear structures, which initially favored intramolecular cross-linking, gradually developed more intermolecular cross-links during reprocessing. Notably, linear samples demonstrated a greater tendency for intermolecular cross-linking than hyperbranched, attributed to their extended linear architecture. These findings highlight the crucial role of polymer topology in dictating cross-link rearrangement pathways during reprocessing, offering insights for designing recyclable polyurethanes with enhanced durability. Major: School of Energy and Chemical Engineering

2025-07-31T15:00:00Z