Rechargeable lithium-ion batteries are necessary for our life to use as a mobile phone, electric vehicle and so on. However, there is a limit to the capacity of lithium-ion batteries. Therefore it is necessary to develop batteries which has large capacity. Lithium-sulfur (Li-S) battery is expected for next generation rechargeable battery owing to have high capacity (1,645 mAh/g) compared with conventional Li-ion batteries. However, Li-S battery has serious problem that lithium polysulfide (Li₂S_x) which is an intermediate product dissolves into electrolyte. If we can suppress the dissolution of Li₂S_x, the battery life should be extended. To suppress the dissolution of Li₂S_x, we use solvate ionic liquid (SIL) electrolytes. SIL is mixture of 1:1 complex from low-molecular weight ether and Li salt, which have high thermal / electrochemical stabilities owing to strong interaction of between ether oxygen and Li cation. SIL electrolytes have low solubility of Li₂S_x owing to their low Lewis acidity / basicity and suppress dissolution of Li₂S_x into electrolyte. Recently, it was found that high Li salt concentration more than 1:1 SIL electrolyte is effective for high performance lithium-ion batteries and Li-S batteries. Fig. 1 shows cycle performance of LiNi_1/3Mn_1/3Co_1/3O₂ | [Li(G3)_x]TFSA | Li cell. Excess Li salts achieved high cycle performances and stable charge-discharge operations. Li salt excess SIL electrolyte contributes to extension of cycle life for Li-ion batteries. According to these previous researches, it is shows that local composition changes of SIL electrolytes of glyme and Li salt near the electrode during the charge and discharge process. Li₂S_x should be dissolved in the released free glyme. Therefore, we considered that Li salt excess SIL electrolyte can suppress the formation of temporary free glyme. Therefore, the purpose of this study is to clarify the influence of the composition of SIL electrolyte on the solubility of Li₂S_x and the performance of Li-S batteries. All preparations and measurements were carried out in an inert atmosphere Ar-filled glove box and a sealed cell. SILs, [Li(G3)_1.25]TFSA, [Li(G3)_1.11]TFSA, [Li(G3)]TFSA, [Li(G3)_0.9]TFSA and [Li(G3)_0.8]TFSA (composition ratio of triglyme (G3) and LiTFSA is 10:8, 10:9, 10:10, 10:9 and 10:8), were prepared, respectively. Viscosity, density and thermal stability of SIL electrolyte samples were measured. Then, dissolution tests of Li₂S_x were carried out. Lithium polysulfide is an unstable substance, so S₈ and Li₂S were mixed with S₈ and Li₂S=7:8, we defined as Li₂S₈ were prepared. Prepared SIL electrolyte and Li₂S₈ were mixed for saturation. SILs were each diluted 50 times (molar ratio) with SIL electrolyte, and the absorbance was measured by UV-vis spectrometer. Fig. 2 shows appearances of five SIL electrolytes with saturated Li₂S₈. It was visually observed that the amount of free glyme decreased in the Li excess SIL electrolyte and the dissolution of Li₂S_x into SIL electrolyte was suppressed with LiTFSA concentration. From this result, improvement of Li-S battery performances were expected by using Li salt excess SIL electrolytes. Charge and discharge tests were carried out using [S|[Li(G3)_x]TFSA|Li] cells, and cycle performances were shown (Fig. 3) . All initial capacities were more than 800 mAh/g. The figure is the normalized cycle characteristics as deterioration rate with the initial capacity set to 100%. At 25 cycles [Li(G3)_x]TFSA x=0.8 (Li salt excess SIL electrolyte) showed a sufficient capacity retention about 10% higher than x=1 (equimolar). From the above results, the Li salt excess SIL electrolyte can conclude as effective electrolyte design for Li-S batteries. In the presentation, we will comprehensively report the thermal and transport properties of each SIL and the results of UV-vis measurement results.