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Modeling the Battery of the Future<br><b>Speaker: Don Siegel (U-M Mechanical Engineering/Applied Physics)</b>

Tuesday, September 27, 2011
12:00 AM
335 West Hall

Speaker: Don Siegel (U-M Mechanical Engineering/Applied Physics)

Thanks to their high theoretical specific energy densities (~11,000 Wh/kg-Li), Li-air batteries are attracting increasing attention as a potentially transformative energy storage technology. Despite this potential, Li-air technology remains in its infancy, and attaining a viable secondary Li-air battery will require that several challenges be overcome. These include: low efficiencies, poor discharge rates, and capacity fade. Although recent studies have demonstrated improvements based on new catalysts and electrolytes, the mechanisms underlying these limitations remain poorly understood. Consequently, optimization of Li-air systems is progressing via trial-and-error.

To accelerate the development Li-air batteries, we apply density functional theory calculations to reveal materials phenomena that may limit performance. Given that rechargeability hinges upon the decomposition of high surface area discharge phases (Li2O2 and Li2O), we have characterized the surface structure and electronic properties of these phases and predicted mass transport phenomena. Regarding surface properties, we find that the stable surfaces of Li2O2 are half-metallic (i.e., conducting in one spin channel), even though Li2O2 is bulk insulator. This behavior differs from that of Li2O, whose low-energy surfaces are insulating, and is consistent with experiments showing superior performance in cells where Li2O2 is the discharge product. Regarding bulk properties, we find that lithium vacancies mediate mass transport in Li2O2 across the range of potentials seen in a typical charge/discharge cycle. In contrast, mass transport of oxygen is severely limited. These results are discussed in light of the high overpotentials observed during charging, and several opportunities for experimental tie-in are highlighted.

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Biography: Don Siegel is an Assistant Professor in the Departments of Mechanical Engineering and Applied Physics at the University of Michigan. His research lies in the field of computational materials science, with an emphasis on the development of energy storage materials and structural alloys for use in the transportation sector. Prior to joining UM he led the Fuel Cell and Hydrogen Storage Materials Group at Ford Motor Company. He is a recipient of an MRS Graduate Student Award, the TMS/JIM International Scholar Award, a National Academies/NRC Fellowship, and a Special Recognition Award from the U.S. Council for Automotive Research. Siegel holds a Ph.D. in Computational Condensed Matter Physics from the University of Illinois at Urbana-Champaign, and had postdoctoral training at Sandia National Laboratories and the U.S. Naval Research Lab.