Innovation in the design of electrolyte materials is crucial for realizing next-generation electrochemical energy storage devices such as Li-S batteries. The theoretical capacity of the S cathode is 10 times higher than that of conventional cathode materials used in current Li-ion batteries. However, Li-S batteries suffer from the dissolution of lithium polysulfides, which are formed by the redox reaction at the S cathode. Herein, we present simple solvate ionic liquids, glyme-Li salt molten complexes, as excellent electrolyte candidates because they greatly suppress the dissolution of lithium polysulfides. The molten complexes do not readily dissolve other ionic solutes, which leads to the stable operation of the Li-S battery over more than 400 cycles with discharge capacities higher than 700 mAh g-sulfur(-1) and with coulombic efficiencies higher than 98% throughout the cycles. Such high performance has not been realized to the best of our knowledge. Furthermore, the addition of a nonflammable fluorinated solvent, which does not break the solvate structure of the glyme-Li salt molten complexes, greatly enhances the power density of the Li-S battery. The strategic design of electrolyte properties provides opportunities for the development of new electrochemical devices with many different electrode materials. (C) 2013 The Electrochemical Society.