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

Abstract

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-Al 2 O 3 ) 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-Al 2 O 3 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 1 H 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-Al 2 O 3 system.