MateriAlZ Seminar: Katharine Harrison

Abstract
Li metal anodes can theoretically enable higher energy density batteries relative to Li-ion batteries, but Li cycling is plagued by poor morphological control. Li plates in high-aspect-ratio morphologies such as dendrites, which can puncture the separator used in batteries and short the electrodes together. Li also reacts parasitically with the electrolyte, causing the irreversible formation of a surface film on Li deposits, which is referred to as the solid electrolyte interphase. We systematically varied applied pressure in pouch cell batteries to quantify its effect on cycling and morphology at varied current densities in solvate electrolytes. We found that pressure can improve performance and morphology at low current densities but too much pressure can degrade performance due to transport issues associated with pore closure in the porous separator. To better understand morphology, we developed a technique to mill through and image in-tact battery stacks in coin cells without disassembly using a cryogenic laser plasma-focused ion beam scanning electron microscope. Images showed that high current density cycling can lead to complete failure of the separator and/or growth of Li into the separator. Using this technique, we showed that applied pressure exacerbates short circuits rather than pressure squashing dendritic growth at high current densities. This work is important for understanding the optimal pressure needed to operate Li metal anode batteries and for understanding the relationships between electrochemistry, transport, and mechanical properties in Li metal anode cells. Sandia National Laboratories is a multimission laboratory managed and operated by National Technology and Engineering Solutions of Sandia, LLC., a wholly owned subsidiary of Honeywell International, Inc., for the U.S. Department of Energy's National Nuclear Security Administration under contract DE-NA-0003525.

Bio
Dr. Katharine Harrison is a principal member of the technical staff at Sandia National Laboratories working in the Nanoscale Sciences Department. She received her B.S. from the University of California San Diego in mechanical engineering. She received her M.S.E. from the University of Texas at Austin in mechanical engineering with a focus on thermal fluid systems. She received her Ph.D. from the University of Texas at Austin in mechanical engineering with a focus in materials science. She has been working in the battery field for 16 years. Her Ph.D. was focused on microwave-assisted solvothermal synthesis and electrochemical/materials characterization of Li-ion battery cathode materials. At Sandia, she has worked on lithiation and sodiation into carbon materials, Si anodes, Li metal anodes, O2 cathodes, and conversion cathodes for next-generation batteries.