Assistant Professor Lee Hyun-Wook
School of Energy and Chemical Engineering, Ulsan National Institute of Science and Technology (UNIST)
Host: Dr Wesley Zheng (Electronic Materials Department (ELE), IMRE)
Extensive research for new energy storage materials has created a high demand for experimental techniques that can provide real-time, single-particle-level information on the dynamic electrochemical processes taking place at the electrode materials during battery charge/discharge cycles. In situ transmission electron microscopy (TEM) on lithium ion batteries has offered exceptional opportunities for monitoring the dynamic processes of electrode materials during electrochemical reaction at both spatial and temporal resolution. In this talk, the speaker will introduce in situ TEM studies on silicon anodes that suffer the anomalous volumetric changes and fracture during lithiation process. Previously, the lithiation behaviour of a single silicon particle system has been explained in detail by simulation data and experimental observation. However, in real batteries, since lithiation occurs simultaneously in clusters of silicon in a confined medium, understanding how the individual silicon structures interact during lithiation in a closed space is necessary. In this regard, the speaker's work demonstrated physical and mechanical interactions of swelling silicon structures during lithiation using well-defined silicon nanopillar pairs.Ex situ SEM and in situ TEM studies reveal that compressive stresses change the reaction kinetics so that preferential lithiation occurs on free surfaces when the pillars are mechanically clamped. Such mechanical interactions enhance the fracture resistance of lithiated silicon by lessening the tensile stress concentrations in silicon structures. The experiment reveals the surprising effects of nanostructure shape, size, and void space for lithiation and the results will contribute to improved design of silicon structures at the electrode level for high-performance lithium-ion batteries.
ABOUT THE SPEAKER
Assistant Professor Lee Hyun-Wook received his B.S. in Advanced Materials Engineering from Sejong University in 2007. Following that, he continued his graduate studies at the Korea Advanced Institute of Science and Technology (KAIST) under the direction of Professor Do Kyung Kim. During his Masters and Ph. D. degree studies, he focused on the research of the synthesis of nanomaterials and Li-ion batteries. In 2012, he moved to a postdoctoral position at Stanford University under the supervision of Professor Yi Cui. At that time, he carried out research on the Prussian Blue open framework structures as electrode materials for Na ion batteries and in situ/operando transmission electron microscopy (TEM) investigations of battery electrode materials under electrochemical reaction. His research interests include rechargeable batteries, synthesis of nanosized materials, and in situ / operando TEM studies.
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