Development of lithium-sulfur batteries using room temperature ionic liquid-based quasi-solid-state electrolytes

Abstract

Quasi-solid-state electrolytes (QSEs), consisting of pseudo-ternary system, i.e., room temperature ionic liquid (RTIL)-lithium bis(trifluoromethanesulfonyl)amide (Li-TFSA)-fumed silica nano particles, were prepared for use as electrolytes in bulk-type all-solid-state cell configuration lithium-sulfur rechargeable batteries. Regardless of the high concentration of RTIL-Li-salt mixtures with fumed silica nano particles, i.e., 80-90% volume ratio, the composites were white powders. Further blending with 5wt% polytetrafluoroethylene (PTFE) powder caused the composite powders to become transparent sheets of 30-200μm in thickness. The electrolyte sheets exhibited liquid-like high apparent conductivities regardless of their solid-like appearance. Sulfur utilization ratios were enhanced using conductive additives with high specific surface areas. Cells with notable performance were successfully assembled after the optimization of the RTIL solvent composition, electrolyte thickness, and conductive additive species. The initial discharge capacity was 1100mAh g−1 at 0.05 C. After 45 discharge-charge cycles, the discharge capacity was still 690mAhg−1. This performance is comparable to lithium-sulfur cells that use the RTIL-Li-salt liquid electrolytes.