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Experimental Investigations on Mechanical and Structural Phenomena in Next-Generation Lithium-ion Battery Materials

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Abstract:
Abstract of “Experimental Investigations on Mechanical and Structural Phenomena in Next-Generation Lithium-ion Battery Materials” by Jung Hwi (Juny) Cho, Ph.D., Brown University, May 2022. Throughout the years at Brown University, I’ve had the privilege of working with next-generation battery materials that are in great interest to the battery community. Further insights gained by investigating unanswered fundamental mechanisms of these materials can provide researchers and engineers to generate innovative ideas and design better performing batteries that are in much demand for electrification. Specifically, the first two parts of my thesis involved looking into electrochemo-mechanical challenges that are present in lithium metal batteries, where poor stability of Li metal / liquid electrolyte or Li metal / solid electrolyte interfaces leads to chronic problems, such as filament formation and capacity loss. These coupled phenomena are challenging to investigate directly, and in-situ curvature measurements are an important tool that can be used to monitor these stresses during battery cycling. Chapter 2 of the thesis shows that when using this technique during Li plating and examining film thickness effects, it is possible to separate contributions from the bulk lithium metal and the solid electrolyte interphase (SEI). The results show that the stresses created in the SEI films from liquid electrolytes are much larger than those in the Li metal and suggest that the design of SEI that promote high stability during plating is the most essential. In Chapter 3, similar in-situ techniques were employed directly on all-solid-state cells, where clarifying the mechanical driving forces of lithium metal penetration through the solid electrolyte is a particularly important challenge. To probe the chemo-mechanical phenomena that occur during lithium plating, the study reports measurements from in-situ curvature cells that were designed to evaluate the stresses that evolve in LLZO during lithium plating. The experiments show that Li metal plating within a surface flaw can produce stress build-up prior to short-circuiting and suggest that it is critical to minimize surface defects and flaws during manufacturing processes. The fourth chapter of my dissertation focuses more on structural phenomena in thin film SiOx electrodes. In particular, the effect of the oxygen content in various compositions of SiOx on their structural change during cycling remains elusive. General rule of thumb for cycling stability in materials requires its inherent structural stability over many cycles, and it is critical to tune the right amount of oxygen in SiOx that would provide structural integrity throughout hundreds of cycles that is required by commercial standards. In this study, various electrochemical and characterization techniques were used to probe the overall structural evolution in different SiOx compositions. The results show that SiOx goes under significant structural change with further cycling, and that the films with higher oxygen content requires additional cycling for the material to restructure and stabilize. Based on similar structure and reversible capacities observed in various SiOx compositions after 100 cycles, additional hypothesis of solid-solution-like behavior is suggested for further investigation.
Notes:
Thesis (Ph. D.)--Brown University, 2022

Citation

Cho, Jung Hwi (Juny), "Experimental Investigations on Mechanical and Structural Phenomena in Next-Generation Lithium-ion Battery Materials" (2022). Materials Science Engineering Theses and Dissertations. Brown Digital Repository. Brown University Library. https://repository.library.brown.edu/studio/item/bdr:nvjctujh/

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