Lithium-sulfur batteries have been regarded as the most promising high-energy electrochemical en-ergy storage device owing to the high energy density,low cost and environmental friendliness.How-ever,traditional lithium-sulfur batteries using ether-based electrolytes often suffer from severe safety risks(i.e.combustion).Herein,we demonstrated a novel kind of flame-retardant concentrated electrolyte(6.5 M lithium bis(trifluoromethylsulphonyl)imide/fluoroethylene carbonate)for highly-safe and wide-temperature lithium-sulfur batteries.It was found that such concentrated electrolyte showed superior flame retardancy,high lithium-ion transference number(0.69)and steady lithium plating/stripping be-havior(2.5 mAh cm-2 over 3000 h).Moreover,lithium-sulfur batteries using this flame-retardant concen-trated electrolyte delivered outstanding cycle performance in a wide range of temperatures(-10 ℃,25 ℃and 90 ℃).This superior battery performance is mainly attributed to the LiF-rich solid electrolyte inter-phase formed on lithium metal anode,which can effectively suppress the continuous growth of lithium dendrites.Above-mentioned fascinating characteristics would endow this flame-retardant concentrated electrolyte a very promising candidate for highly-safe and wide-temperature lithium-sulfur batteries.