Highly Safe Electrolyte Enabled via Controllable Polysulfide Release and Efficient Conversion for Advanced Lithium–Sulfur Batteries

Conventional lithium-sulfur batteries often suffer from fatal problems such as high flammability, polysulfide shuttling, and lithium dendrites growth. Here, highly-safe lithium-sulfur batteries based on flame-retardant electrolyte (dimethoxyether/1,1,2,2-tetrafluoroethyl 2,2,3,3-tetrafluoropropyl ether) coupled with functional separator (nanoconductive carbon-coated cellulose nonwoven) to resolve aforementioned bottle-neck issues are demonstrated. It is found that this flame-retardant electrolyte exhibits excellent flame retardancy and low solubility of polysulfide. In addition, Li/Li symmetrical cells using such flame-retardant electrolyte deliver extraordinary long-term cycling stability (less than 10 mV overpotential) for over 2500 h at 1.0 mA cm^-2 and 1.0 mAh cm^-2 . Moreover, bare sulfur cathode-based lithium-sulfur batteries using this flame retardant electrolyte coupled with nanoconductive carbon-coated cellulose separator can retain 83.6% discharge capacity after 200 cycles at 0.5 C. Under high charge/discharge rate (4 C), lithium-sulfur cells still show high charge/discharge capacity of ≈350 mAh g^-1 . Even at an elevated temperature of 60 °C, discharge capacity of 870 mAh g^-1 can be retained. More importantly, high-loading bare sulfur cathode (4 mg cm^-2 )-based lithium-sulfur batteries can also deliver high charge/discharge capacity over 806 mAh g^-1 after 56 cycles. Undoubtedly, the strategy of flame retardant electrolyte coupled with carbon-coated separator enlightens highly safe lithium-sulfur batteries at a wide range of temperature.