Mass transport properties in quasi-solidified lithium-ion conducting ionic liquids at oxide particle surfaces

Lithium-ion conducting RTIL–Li-salt mixtures, 1MLi-TFSA/EMI-TFSA and 1MLi-FSA/EMI-FSA, were quasi-solidified at fumed SiO2 particle surfaces. The electrical conductivities and the self-diffusion coefficients of the constituent species of the RTIL–Li-salt bulks and the composite materials, x vol%1MLi-TFSA/EMI-TFSA–fumed SiO2 and x vol%1MLi-FSA/EMI-FSA–fumed SiO2 (x = 100, 75 and 50), were evaluated. We have successfully quasi-solidified RTIL–Li-salts at fumed SiO2 surfaces even though most of the composites are consisting of RTIL–Li-salts such as x = 75–80. The quasi-solid-state composites had liquid-like high electrical conductivities, e.g. 3.2 × 10− 4 to 4.4 × 10− 3 S cm− 1 for 75 vol%1MLi-TFSA/EMI-TFSA–fumed SiO2 and 6.4 × 10− 4 to 5.4 × 10− 3 S cm− 1 for 75 vol%1MLi-FSA/EMI-FSA–fumed SiO2, in the temperature range of 283–348 K. The self-diffusion coefficients of all constituent species become small as volume ratio of RTIL–Li-salt mixtures decreased. The effect of fumed silica surface on the transport properties of the RTILs depended on the RTIL structures. By receiving the effect from fumed silica surfaces, the disassociation of the ion pair, [EMI+][TFSA−], progressed for 1MLi-TFSA/EMI-TFSA while the Li-containing species lost their diffusivities for 1MLi-FSA/EMI-FSA.