(4kf) Multi-Faceted Roles of Lithium Metal in Batteries and Electrocatalysis Revealed By Cryo-EM

Electrochemical energy conversion and storage is critical for advancing vehicle electrification and sustainability of essential commodity chemicals. In pursuit of these goals, I delved progressively deeper into the foundational research of batteries and beyond: (1) pioneering novel methodologies to fundamentally understand reactive metal deposition, (2) regulating electrolyte decomposition to enhance lithium (Li) metal batteries (LMBs) performance, and (3) expanding the technology’s applicability to make impact beyond batteries.

I have revealed the intrinsic morphology of electrodeposited Li metal to be a non-dendritic rhombic dodecahedron, which defies conventional expectations yet aligns with the theoretical prediction. Li deposition is a process in which Li-ions are reduced to metallic form at the electrode, which plays a crucial role for LMBs, because the reversibility of deposition morphology directly determines the cycling performance and safety of the battery. However, the simultaneous formation of a surface corrosion film termed the solid electrolyte interphase (SEI) complicates the deposition process, which underpins our poor understanding of Li metal electrodeposition. I creatively integrated the classical electrochemical method, ultramicroelectrode geometry, and an emerging electron microscopy technique, cryogenic electron microscopy (cryo-EM), to decouple Li deposition from the SEI growth and capture the corresponding nanostructure of Li. This discovery has significant implications for LMBs, as it suggests SEI influence can be effectively mitigated to achieve desired deposition morphologies. Besides enhancing our understanding of Li deposition, I extended this finding to other reactive alkali metal, such as sodium metal that was found to exhibit the same polyhedral structure when outpacing the SEI influence. This emphasizes the applicability of my findings and opens new opportunities to explore how reactive metal deposition fundamentally proceeds without the influence of corrosion film, thereby regulating reversibility of metal deposition to optimize the performance of metal batteries.

In addition to deposition morphology, the properties of the SEI also influence the performance of LMBs, as the SEI governs the transportation of Li-ion during cycling. Since the SEI formation results from electrolyte decomposition influenced by electric fields, I systematically examined effects of both electrolyte decomposition and electric fields on SEI formation, progressing from the bulk electrolyte to the electrode surface. I worked with colleagues to quantify reactions driving SEI formation and determine decomposition rates of individual components within the electrolyte, guiding us design and prioritize the decomposition of electrolyte components. Furthermore, I emphasized the importance of electric field to further fine-tune the formation of favorable SEI to improve battery performance.

Looking beyond applications of Li metal in batteries, I leveraged the wealth of battery knowledge and established strategies to investigate fundamental aspects of Li metal as electrocatalyst in electrifying ammonia synthesis to help decarbonize the traditional chemical industry. I revealed key driver behind surface phenomena is the rupture of the SEI, enabling nitrogen and electrolyte to penetrate and react with Li metal to make ammonia. The insights from this work expanded our perspective of how Li metal electrodeposition can decarbonize chemical synthesis and inform our future efforts in designing better LMBs as well.

Research Interests

My future research will leverage knowledge in materials design, electrochemistry, and advanced characterizations, expertise that I developed in my graduate work. I will address both the practical and fundamental challenges in electrochemical systems within two major groups: (1) engineering design guided by (2) fundamental understanding. The synergy between these two thrusts will not only bring practical applications in the short-term, but also discover new foundations to build long-term solutions. Here, I propose to apply electrochemical methods and advanced characterization techniques (e.g. cryo-EM) to answer key questions that have long eluded scientists. These insights will simultaneously drive efforts in my lab for breakthroughs in engineering and design toward their practical application.

1. Understand interfacial phenomenon

I will leverage microscopy and spectroscopy to elucidate the atomic and molecular structures of interfaces in selected electrochemical systems (e.g., lithium metal batteries, electrocatalysis, etc.)

2. Manipulate interfacial behaviors

I will develop materials (e.g., polymers) and strategies (e.g., diffusion, reaction kinetics, etc.) to tailor interfacial properties and improve electrochemical performance.

3. Correlative microscopy in electrochemical systems

I will couple optical microscopy and electron microscopy to reveal the processes occurring during electrochemical reactions across different length scales (bridging macro to micro) and timescales.

Teaching Interests

My teaching philosophy is inspired by teachers who brought their subjects to life. One impactful learning experience was when an instructor explained reaction kinetics through the Maillard reaction, also known as nonenzymatic browning, using the preparation of braised pork as an example. These lessons were highly effective because they extended beyond the classroom and connected with everyday life, making these interdisciplinary connections created a more lasting impact. Reinforcing such connections and illustrating the multidisciplinary nature of science will be a central part of my teaching mission to prepare young scientists to think critically in any field they enter.

As the head teaching assistant for Fundamentals of Chemical and Biomolecular Engineering (CH ENGR 100) at UCLA, I created and delivered numerous discussions, held weekly office hours, and designed homework problems and exams. I often drew from my chemical engineering background to make useful analogies for critical concepts in the classroom, while also utilizing hands-on demonstrations to connect theory to application. By coupling abstract scientific topics (e.g. chemical potential) to technology (e.g. Li-ion batteries), I successfully conveyed difficult concepts to a broad audience and received positive evaluations.

For the future courses, I anticipate teaching fundamental chemical engineering courses involving principles, thermodynamics and kinetics of chemical reactions. As an undergraduate and graduate both in chemical engineering, my broad exposure to these concepts from various viewpoints grants me valuable perspective as an instructor. I also am enthusiastic about developing future courses that delve into the essential theories and practical applications of electrochemical energy technologies, with a great potential to prepare next-generation scientists and engineers to solve significant energy challenges.

Selected Honors

MIT ChemE Rising Stars (2024)

MRS Graduate Student Gold Award (2024)

UCLA 4th Year Symposium Department Award (2024)

UCLA Dissertation Year Fellowship (2024)

ACS I&EC Graduate Student Award (2023)

NSF BioPACIFIC MIP Affiliate (2022)

UCLA Graduate Fellowship (2020-2022)

Selected Publications

1. X. Yuan, B. Liu, M. Mecklenburg, and Y. Li*, Ultrafast deposition of faceted Li polyhedra by outpacing SEI formation. Nature 2023, 620, 86-91. (Cover Image)
2. K. Steinberg#, X. Yuan#, C. K. Klein, N. Lazouski, M. Mecklenburg, K. Manthiram*, and Y. Li*, Imaging of nitrogen fixation at lithium solid electrolyte interphases via cryo-electron microscopy. Nat. Energy 2023, 8, 138-148.
3. X. Yuan, S. Chen, D. Cheng, L. Li, W. Zhu, D. Zhong, Z.J. Zhao, J. Li, T. Wang, and J. Gong*, Controllable Cu0-Cu+ Sites for Electrocatalytic Reduction of Carbon Dioxide. Angew. Chem. Int. Ed. 2021, 60, 15344-15347.
4. X. Yuan#, L. Zhang#, L. Li, H. Dong, S. Chen, W. Zhu, C. Hu, W. Deng, Z.J. Zhao, and J. Gong*, Ultrathin Pd-Au shells with Controllable Alloying Degree on Pd Nanocubes toward Carbon Dioxide Reduction. J. Am. Chem. Soc. 2019, 141, 4791-4794. (Cover Image)