The major bottleneck in the development of safe and high energy density lithium-based batteries is the lack of a suitable electrolyte needed to eliminate the flammable liquid carbonate electrolyte solvents in use today. Among replacement candidates are a broad array of solid electrolytes based on inorganic oxides and sulfides, ionic liquids (ILs) immobilized in a pseudo-solid matrix, and polymers. Our laboratory is focused on application of various nuclear magnetic resonance (NMR) techniques to help understand structure and dynamics of energy storage materials, in particular novel electrolytes. In this presentation we discuss three recent collaborative efforts. (i) The first topic, in collaboration with Oak Ridge National Lab (E. Self, J. Nanda), is on composites of highly conducting β-Li3PS4 and poly(ethylene oxide) (PEO), where multinuclear (1H, 6,7Li, 31P) MAS NMR is used to elucidate the structural changes and reduction in crystallinity of the baseline compound by PEO incorporation. (ii) In collaboration with UCLA (B. Dunn, D. Ashby), we have investigated ionogels, which are pseudo-solid-state electrolytes consisting of the IL BMIM TFSI plus LiTFSI salt electrolyte confined in a mesoporous silica matrix. We report here NMR measurements of ionic self-diffusion coefficients as well as fast field cycling broadband relaxometry with emphasis on elucidating confinement effects of the silica matrix on ionic transport. (iii) With Ionic Materials, Inc. (M. Zimmerman, R. Leising), we discuss results for a solid polymeric electrolyte based on semicrystalline polyphenylene sulfide and Li salts such as LiTFSI and LiFSI. This polymer electrolyte can be reliably extruded into thin films, is non-flammable, has attractive mechanical properties for lithium dendrite suppression, is electrochemically stable against Li, and is compatible with a variety of different cathodes, including NMC811. NMR diffusometry measurements reveal Li room temperature self-diffusion coefficients that are the highest in any known solid.

NMR investigation of structure and transport in a diverse set of solid electrolytes for Li batteries

ACS Fall 2020 Virtual Meeting

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