Electrical Conductivity, Self-Diffusivity and Electrolyte Performance of a Quasi-Solid-State Pseudo-Ternary System, Bis(trifluoromethanesulfonyl)amide-Based Room Temperature Ionic Liquid–Lithium Bis(trifluoromethanesulfonyl)amide–Fumed Silica Nanoparticles

Quasi-solid-state electrolyte consisting of a pseudo-ternary system, RTILs – Li-TFSA – fumed silica nanoparticles, were prepared for use as electrolytes of the all-solid-state lithium rechargeable battery. EMI-TFSA, DEME-TFSA and PP13-TFSA were chosen as RTIL solvents. It was found that the pseudo-ternary composites had liquid-like high ionic conductivity as well as self-diffusion coefficients in spite of the solid-like appearances regardless of RTIL solvent species. Stability of the quasi-solid-state electrolytes to lithium electrodes was investigated by lithium symmetric cells with ac and dc techniques. All-solid-state bulk cells were assembled and the charge – discharge characteristics were evaluated. A stable charge – discharge cycles could be performed with high cathode utilization ratios such as above 85% with comparatively lower c-rates. At higher c-rates, the discharge capacities of our all-solid-state cells using the quasi-solid-state electrolytes are smaller than that using a conventional organic electrolyte with a separator. This suggests that the power density of our all-solid-state cells is essentially limited by slow lithium-ion transport similarly to RTIL – Li-salt mixtures. Based on the above results, the correlation between the charge – discharge cycling performance of our all-solid-state cells and the stabilities of the quasi-solid-state electrolytes were discussed.