Probing Degradation Mechanisms and Structural Analysis of Solid Electrolytes by Diverse Analyses Including Cryogenic Electron Microscopy

Research on the interface between solid electrolytes (SE) and electrode materials is of vital importance for the development of various battery systems, including all-solid-state batteries, solid oxide fuel cells, and metal-air batteries. The complex electro-chemo-mechanical evolution of the electrode or catholyte/SE interface can diminish cell performance. For a detailed understanding, transmission electron microscopy (TEM) analysis could be a straightforward method for disclosing the microstructures. Unfortunately, direct capturing for light element species, such as lithium metal and sulfide SE materials via conventional TEM has been unsuccessful because of their vulnerability toward the electron beam. In this regard, cryogenic TEM, which has been emerging as a powerful tool for observing electron-beam-sensitive materials, could be highly promising for sulfide SE materials. There have been no reports on the cryogenic TEM measurement of sulfide SE materials thus far.<br/>In the first part, I would like to provide insights into the interfacial studies on steady and dynamic states and during the operation of hybrid Na-seawater batteries. Advantages of liquid catholyte can be applied to the model to understand underlying phenomena of the SE due to the homogeneous ion fluxes into solid electrolytes. Chemical stability variations at a steady-state can severely affect battery performance. Seawater batteries fabricated with NASICON in immersed DI water for 1 year exhibit a large resistance region from the first cycle; this system breaks down before 200 h, unlike a cell fabricated using NASICON immersed for 1 year in a marine environment. In the second part, I would like to introduce cryogenic TEM analyses on diverse sulfide SE. The essential findings from cryogenic TEM will unveil the unknown areas that have been known as formidable challenges in sulfide electrolytes, such as the visualization of Li⁺ migration paths and electrochemically driven interfacial evolution.<br/><b>Reference</b><br/>1. T-U. Wi^§, C. Lee^§, M. F. Rahman^§, W. Go, S. H. Kim, D. Y. Hwang, S. K. Kwak*, Y. Kim*, <b>H.-W. Lee</b>*, “Chemical stability and degradation mechanism of solid electrolytes/aqueous media at a steady state for long-lasting sodium batteries”, <b><i>Chemistry of Materials</i></b>, <b>33</b> (1) 126-135 (2021).<br/>2. C. Lee^§, T.-U. Wi^§, W. Go, M. F. Rahman, M. T. McDowell, Y. Kim*, <b>H.-W. Lee</b>*, “Unveiling interfacial dynamics and structural degradation of solid electrolytes in a seawater battery system”, <b><i>Journal of Materials Chemistry A</i></b>, <b>8</b> (41) 21804-21811 (2020).<br/>3. Y. B. Song, D. H. Kim, H. Kwak, D. Han, S. Kang, J. H. Lee, S.-M. Bak, K.-W. Nam, <b>H.-W. Lee</b>*, Y. S. Jung*, “Tailoring solution-processable Li argyrodites Li_6+<i>x</i>P_1-<i>x</i>M<i>_x</i>S₅I (M = Ge, Sn) and their microstructural evolution revealed by cryo-TEM for all-solid-state batteries”, <b><i>Nano Letters</i></b>, <b>20</b> (6) 4337-4345 (2020).