Solid–Liquid Interfacial Properties Related to Ionic Conductivity of Mixtures of Metal Oxide Particles and Lithium Bis(fluorosulfonyl)amide-Sulfone Electrolytes

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We evaluated and compared the physical properties of electrolyte solutions consisting of lithium bis(fluorosulfonyl)amide and sulfone solvents (molar ratio = 1 : 3) and their mixtures containing aluminum oxide (α-Al₂O₃) or lithium lanthanum zirconate (LLZ) particles of various particle sizes. Sulfolane (SL), 3-methylsulfolane, and ethyl isopropyl sulfone were evaluated as sulfone solvents for the electrolyte solutions. The phase-change heat, phase-change temperature, and spin–spin relaxation time in nuclear magnetic resonance (NMR) measurements decrease in a mixture of SL electrolyte with a metal oxide, with an apparent average liquid thickness in the order of nm resulting from the SL electrolyte solution. This indicates a decrease in molecular mobility around the particle surface. For the α-Al₂O₃ system, no substantial changes are observed in the activation energy of ionic conductivity, self-diffusion coefficient of Li⁺ (determined via pulsed-field gradient NMR), or relative cross-peak intensities of Li⁺ and ¹H of SL in the two-dimensional NMR of the mixture. Therefore, despite its low molecular mobility, the SL electrolyte solution at the solid–liquid interface is considered to exhibit an ionic conductivity mechanism similar to that of the bulk electrolyte. It was suggested that LLZ system has a different ionic conduction mechanism than α-Al₂O₃ system.