CAREER: Designing Interfaces for Electrochemical Energy Storage: A Mechanistic Perspective

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This CAREER project focuses on lithium-sulfur (Li-S) batteries, which promise lower cost and higher capacity in next-generation energy storage systems. Advanced lithium batteries for vehicles and energy storage could improve domestic energy security, but their use is mainly limited by undesirable chemical side reactions at the electrode/electrolyte interface. This project seeks to fundamentally understand the reactions at this interface during battery operation. This fundamental understanding will help resolve the issues of battery stability and overall battery performance. The education and outreach activities associated with this project are to (i) provide hands-on experience to high school students and middle school students, (ii) engage undergraduate students in cutting-edge research activities with strong emphasis on the involvement of underrepresented students in STEM and (iii) provide innovation and entrepreneurship exposure to graduate students.While Li-S batteries have been extensively explored, many aspects of the mechanisms of polysulfide redox reactions at solid/liquid electrolyte interfaces remain unclear. In the absence of detailed mechanistic understanding, rational design of electrode architectures has been difficult. The technical objective of this project is to map the temporal and spatial evolution of polysulfide speciation during the charge/discharge process in a Li-S battery through use of in-situ scanning electrochemical microscopy methods coupled with Raman spectroscopy (SECM-Raman). The research program is underpinned by two guiding hypotheses; (1) measuring interfacial properties will allow for mechanistic elucidation of (electro)chemical reaction pathways and provide information on kinetics of polysulfide dissolution-disproportionation-precipitation and (2) elucidating the reaction mechanism will control the electrochemical interface and thereby polysulfide-shuttle with an appropriate material design. The successful completion of the project is expected to (i) enhance fundamental understanding of interactions at the electrode/electrolyte interface at the nanoscale level with high spatiotemporal resolution using a new analytical tool, (ii) map the interaction of polysulfides with the electrode surface and with electrolyte solvents under transient conditions with a high temporal resolution, and (iii) define the role of catalysts and the rate-limiting step in the overall polysulfide redox process to assess superior performance of materials for Li-S batteries. The resulting mechanistic elucidation of sulfur (electro)chemical reactions occurring at the interfaces will provide new insight into Li-S redox chemistry and will allow for detailed mapping of the spatial and temporal evolution of the polysulfide shuttle; a core issue in the Li-S system.