CAREER: Electro-Chemo-Mechanics of Li and Na Metal: Toward Dendrite- and Damage-Free Metallic Anodes of Rechargeable Batteries

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Non-Technical Summary:Rechargeable batteries are everywhere in daily life. Indeed, lithium-based batteries have become the power source of choice in portable electronics and electric vehicles. Still, commercial batteries utilize materials with relatively low energy densities; they add substantial weight to vehicles and occupy huge volumes in portable electronics but must be re-charged every few hours. Owing to their enormous energy densities, batteries 'beyond lithium-ion' based on metallic lithium and sodium have emerged, primed to meet growing demands. However, these systems suffer from severe issues of degradation and safety that have precluded their practical use. Materials and mechanics-based studies are thus necessary to enable safe and durable operation. Accordingly, the goal of this project is to provide understanding of the interplay between functional and structural behavior of lithium and sodium metal anodes, combined with materials discovery of alloys. These studies will guide appropriate charging conditions, applied pressures, and material properties that prevent damage. Overall, advances in batteries will benefit the USA by reducing harmful emissions, improving safety, enhancing infrastructure, and securing energy independence. Commercializing lithium anodes would dramatically increase energy densities (up to ~4x) of portable electronics and electric vehicles, while commercializing sodium anodes may enable grid-scale storage of renewable energy. The broader objectives of this proposal include leveraging established programs to provide research experiences for military veterans and underrepresented minorities. The project will also develop immersive augmented/virtual reality (AR/VR) learning modules to enhance students’ understanding of the interplay among mechanics, microstructure, chemistry, and electric fields in materials for energy storage and conversion. Outreach activities will involve K-12 students and teachers to increase awareness of clean energy technologies.Technical Summary:While the electrochemistry of lithium and sodium has received extensive study, at the heart of the issues outlined above lies a mechanics of materials problem: unstable deformation occurs during operation, producing dendrites and damage. Complicating this matter is that due to their extreme chemical reactivity in air, relatively little is known regarding even the basic mechanical properties of lithium and sodium, e.g., sodium’s room temperature plastic properties and deformation mechanisms remain largely unknown. Even less is known regarding stresses developed during electrodeposition, time/temperature-dependent behavior, fracture and fatigue behavior, how alloys modify properties, and their corresponding influence on microstructural stability. This project will fill in these gaps in fundamental knowledge through testing the following hypotheses: (1) time-dependent plastic deformation dominates the mechanical behavior of lithium and sodium metal; (2) specific alloys enhance creep resistance, promoting structural stability; (3) stresses develop during electrodeposition that can damage surrounding layers and the metals themselves; and (4) pre-loads applied to electrode stacks promote microstructurally stable deposition. To test these hypotheses, this project will utilize unique experimental facilities and develop theoretical models to connect the evolution of mechanical properties, stress, and deformation to chemical and microstructural changes during electrochemical cycling. From the educational perspective of this proposal, textbooks seldom cover coupled phenomena in electro-chemo-mechanics. This project will develop AR/VR modules to fill these voids, which will be integrated into undergraduate/graduate curricula, shown at K-12 outreach activities, shared with K-12 teachers, and made available online. This project will also enable students in materials and mechanics to work in areas not conventionally open to the discipline (electrochemistry) to encourage interdisciplinary research careers.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.