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High energy density and cycling stability of lithium-based batteries are receiving great attention as they have become essential for everyday life, from portable devices to Electric Vehicles(EVs). Charging/discharging of the cell inevitably accompanies dynamic changes such as nucleation and growth of Li, phase transition of cathode materials, and Solid-Electrolyte Interphase (SEI) formation, which are closely related to the electrochemical performance.
Our research focuses on directly visualizing such changes of materials in battery systems, from which we can obtain fundamental knowledge for improving the stability of the LIB systems. In situ transmission electron microscopy (TEM) enables direct observation of nanoscale dynamics in battery systems by providing chemical and crystallographic information of component materials. We investigate various phenomena in battery systems including synthesis of electrode material, (dis)charging, and thermal effect by using in situ Liquid-Phase TEM (LPTEM), in situ biasing/heating TEM and cryo-TEM, with a combination of bulk in situ characterization methods such as in situ XRD and in situ Raman.

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In Situ Analysis of Lithium Ion Battery

Lithium (Li) metal is the most promising alternative anode material for the conventional graphite anode due to its extremely high theoretical capacity. It is important to understand the dynamics of Li nucleation and growth in the early stages, because of their influence on heterogeneous Li growth that deteriorates the performance and safety of lithium metal battery (LMB). In this aspect, we investigated single particle nucleation events and subsequent early stage growth using LPTEM, and studied the associated SEI structures with cryo-TEM. We investigate chemical composition, uniformity, and mechanical property of SEI and how they collectively determine the dynamics of nucleation and initial growth in different electrolyte systems. 

Interface Chemistry in Solid-State-Battery

In all-solid-state-batteries, understanding the interfacial phenomena is highly important to decrease interfacial resistance, which is major bottleneck for long cycle life. We are especially interested in lithium growth at the interface between the anode and solid electrolyte and the thermal stability at the interface between the cathode and solid electrolyte. With this purpose, an integrated analysis platform is established using in situ biasing/heating TEM, in situ optical microscopy, and focused ion beam (FIB) for direct imaging of interfacial chemistry. We expect that our fundamental research on interfacial phenomena will provide novel insights for material design, homogeneous Li plating, and synthesis of stable composite cathode in all-solid-state batteries. 

Raman Microscopy/Spectroscopy of Lithium Ion Battery

Raman microscopy/spectroscopy provides detailed information for chemical bonding, phase, and crystallinity of component materials in LIB, while it enables a large-area analysis in a scale scanning the entire electrode units. Our research aims to develop a cross-sectional in situ Raman platform to study depth-dependent electrochemical reactions of LIB systems. Using this platform, we investigate the origins of (de)lithiation inhomogeneity and the degradation of electrode materials.
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