Interfacial Conductivity Enhancement and Pore Confinement Conductivity-Lowering Behavior inside the Nanopores of Solid Silica-gel Nanocomposite Electrolytes

Abstract

Solid nanocomposite electrolytes (nano-SCEs) that exhibit higher ionic conductivity than the individual confined electrolyte were investigated for high-performance solid-state batteries. Understanding the behavior of Li-ion conduction through the pores is important to design ideal nanoporous structures for nano-SCEs, which are composed of an ionic liquid electrolyte (ILE) in a highly porous (∼90%) silica matrix. To establish the relationship between the pore structure of the silica matrix and the ionic conductivity of the solid nanocomposite, the liquid electrolyte fraction was successfully extracted from the nano-SCE to reveal the fragile porous silica matrix. A careful drying using the CO 2 supercritical drying method helps in sustaining the original structure, preventing its collapse due to surface tension. The pore size distribution, Brunauer−Emmett−Teller (BET) surface area, and porosity were characterized using scanning electron microscopy, transmission electron microscopy, and N 2 adsorption/desorption techniques. Our results revealed a wide size distribution of macropores and mesopores in the silica matrix. The pore size increased and the effective surface area decreased with increasing ILE/SiO 2 molar ratio. The interface conductivity enhancement was found to increase with the thickness of the adsorbed (ice-like) bound-water layer on the silica surface, confirming that the strong hydrogen bonding of the adsorbed ionic liquid molecules on the bound-water layer causes the conduction promotion effect in the nano-SCE. In addition, a large number of small pores lead to a severe pore confinement effect that results in a decreased conductivity due to the increasing viscosity of the ILE filling the pores. The conductivity can be improved by realizing a nano-SCE with an optimized pore size to minimize the pore confinement effect.

Ionic guest in ionic host: ionosilica ionogel composites via ionic liquid confinement in ionosilica supports

“…The ionic conductivity increases while increasing the amount of incorporated IL. Thus, TS 12 IL displays an ion conductivity of ca. 0.32 S m À1 that is more than four orders of magnitude higher compared to TS 1 IL (ca.…”

“…30 nm to maximize the so-called ‘surface conduction promotion effect’ while minimizing the detrimental effect of pore confinement on lithium-ion conduction. 12 All these examples highlight that confinement effects strongly modify the physico-chemical properties of confined ILs with respect to the bulk.…”

Physicochemical Properties of Bis(fluorosulfonyl)amide-Based Ionic Liquids Mixed with Mg and Sr Doped Cubic Li₇La₃Zr₂O₁₂ Powder

“…Solid-state 19 F NMR measurements were performed by ECA600II (JEOL RESONANCE, Japan; Larmor frequency: 564.73 MHz for 19 F at 14.1 T; 3.2 mm magic-angle spinning probe). The LLZ-IL mixture was placed in a 3.2 mm outer-diameter ZrO 2 rotor.…”

“…14,16,17 It is known that the physical properties of liquids that exist on a solid surface differ from their bulk properties. Ionic conductivity 14,18,19 and thermal behavior 20,21 of ILs at interfaces have been analyzed and reported. Relaxation times of nuclear magnetic resonance (NMR) signals from adsorbed IL molecules are also expected to decrease due to their lower molecular mobility 22 than in the bulk IL.…”

“…In this study, we evaluated ionic conductivity, thermal properties by differential scanning calorimetry (DSC), and 19 F NMR spectra of LLZ-IL mixtures to determine the relationships between these physical properties and mixture ratios to elucidate the structure of the LLZ-IL boundary. We selected 1-methyl-1-propylpyrrolidinium bis(fluorosulfonyl)amide (P13FSA) and 1-ethyl-3-methylimidazolium bis(fluorosulfonyl)amide (EMIFSA), which are being evaluated for use in lithium-ion batteries because of their wide electrochemical window, chemical stability, and high ionic conductivity.…”