[CCoE Notice] Dissertation defense announcement_Guangxia Feng

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[Dissertation Defense Announcement at the Cullen College of Engineering]
Study the Interfacial Chemical Reactions on the Battery Electrode using in-operando Imaging Techniques
Guangxia Feng

September 27, 2022; 11:00 AM - 1:00 PM (CST)
Location: Online via ZOOM
Zoom:  https://urldefense.com/v3/__https://uh-edu-cougarnet.zoom.us/j/98586965863__;!!LkSTlj0I!EIbBoV42hPZqcmliHaLVdXyItDYy2El5RJrA_SK45RQBfowy-VFLfBR2P1RiwuC58DXO3ribNpeM_nLARsUy_hYqjo4$  <https://urldefense.com/v3/__https://www.google.com/url?q=https:**Auh-edu-cougarnet.zoom.us*j*91275322202*pwd*3DakhuU1hncVFsZWFYUVRWTEZXOTZZQT09&source=gmail-html&ust=1663170506335000&usg=AOvVaw2cgZ-rF3PxlU7IfQAD6aVU__;Ly8vLz8l!!LkSTlj0I!BeHt2kshU5UxB0meJUuHWDB_Wn2sMPXHDc9M9LvZpYlu5B9v2DkRpOA2lmtC_TbFCz7QbPtEyc61F0sm$>



Committee Chair:
Xiaonan Shan, Ph.D.

Committee Members:
David Mayerich, Ph.D. | Wei-Chuan Shih, Ph.D. | Wu Xu, Ph.D. | Yan Yao, Ph.D.

Abstract

The quality of the solid-electrolyte interphase (SEI) determines the lithium-based batteries' performance. However, the understanding of SEI formation and stripping processes across the electrode interface is still limited due to the lack of in-situ characterization tools. Here, we developed an in-situ reflection interference microscope (RIM) to study and image the local SEI formation and evolution dynamics in conventional LiPF6/carbonate electrolytes with and without 50 ppm water additive. The RIM provides high sensitivity to imaging the minimal signals caused by SEI layer and allows us to observe the entire growth and stripping process of SEI in real-time. The results show that the SEI formation and stripping process consists of multiple steps. The developed RIM enables mapping the SEI sub-layers, calculating thickness information of SEI and studying the influence of electrolyte additive at the same time.The results demonstrate that 50 ppm of water as an additive in electrolyte results in a much thicker and higher quality LiF-rich SEI layer, which leads to a thinner organic SEI deposition, less electrolyte consumption, and more uniform Li nucleation on the electrode surface. The mapped LiF-rich and organic SEI layers' distributions at different potentials indicate that there exist strong reverse correlations between the LiF-rich SEI layer and the organic SEI layer: a thicker LiF-rich layer leads to a thinner organic SEI layer deposited on the electrode and vice versa. The real-time visualization of SEI dynamics achieved for the first time in this work provides a guideline for the rational design of interphases, a battery component that has been the least understood and most challenging barrier to developing electrolytes for future batteries.

Besides the SEI formation dynamics and spatial characteristics, the Li nucleation also plays critical role in battery performance. Non-uniform lithium growth will cause significant volumetric expansion of the lithium metal anode and break the formed SEI, leading to more electrolyte consumption and aggravating the dendrites formation.  The developed RIM also enables the real-time imaging of the entire Li nucleation process with high spatial and temporal resolutions. The RIM allows us to image and track the individual Li nuclei’s sizes and locations continuously throughout the deposition and stripping processes. Different particles start the nucleation at different time points and grows at different speeds, which strongly indicates the localized surface electrochemical environments, including SEI, ion concentration, and surface energy, will determine the Li nucleation and growth. To further illustrate this effect, we extract the localized overpotential map using the particle size dynamics obtained from the RIM and the Barton’s model. The real-time visualization of Li nucleation dynamics and the localized overpotential map achieved for the first time in this work provides a guideline for the battery interphases design to developing high efficient future batteries.

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Guangxia Feng
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