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Lithium-sulfur (Li-S) batteries are drawing huge attention as attractive chemical power sources. However, traditional ether-based solvents (DME/DOL) suffer from safety issues at high temperatures and serious parasitic reactions occur between the Li metal anodes and soluble lithium polysulfides (LiPSs). Herein, we propose a polysulfide-suppressed and flame-retardant electrolyte operated at high temperatures by introducing an inert diluent 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl (TTE) into the high-concentration electrolyte (HCE). Li dendrites are also efficiently suppressed by the formed LiF-rich protective layer. Furthermore, the shuttle effect is mitigated by the decreased solubility of LiPSs. At 60 °C, Li-S batteries using this nonflammable ether-based electrolyte exhibit a high capacity of 666 mAh g^-1 over 100 cycles at a current rate of 0.2C, showing the greatly improved high-temperature performance compared to batteries with traditional ether-based electrolytes. The improved electrochemical performance across a range of temperatures and the enhanced safety suggest that the electrolyte has a great practical prospect for safe Li-S batteries.