Speaker：Dr. Hyun-Wook Lee , Ulsan National Institute of Science and Technology (UNIST)
Invited by：Prof. Sun Yongming
Time：15:00-16:30, September 28, 2018
Venue: A101
Abstract:
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, I 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. 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. This 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.
Biography：
Hyun-Wook Lee is currently an assistant professor in the School of Energy and Chemical Engineering at Ulsan National Institute of Science and Technology (UNIST). He received his B.S. in Advanced Materials Engineering from Sejong University in 2007. After receiving his Bachelor of Engineering degree, he continued his graduate studies at Korea Advanced Institute of Science and Technology (KAIST) under the direction of Prof. Do Kyung Kim. He received his Masters of Science and Ph. D. in Materials Science and Engineering in 2009 and 2012. During his Masters and Ph. D. degree studies, his research focused on the synthesis of nanomaterials and Li-ion batteries. In 2012, he moved to a postdoctoral position at Stanford University under the supervision of Prof. 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. As the first author or co-author, he published 15 research papers in Nature Energy (4), Nature Nanotechnology (5), and Nature Communications (6).
