Recent progress in fluorinated electrolytes for improving the performance of Li-S batteries

Lithium-sulfur (Li-S) batteries represent a beyond Li-ion technology with low cost and high theoretical energy density and should fulfill the ever-growing requirements of electric vehicles and stationary energy storage systems. However, the sulfur-based conversion reaction in conventional liquid electrolytes results in issues like the so-called shuttle effect of polysulfides and lithium dendrite growth, which deteriorate the electrochemical performance and safety of Li-S batteries. Optimization of conventional organic solvents (including ether and carbonate) by fluorination to form fluorinated electrolytes is a promising strategy for the practical application of Li-S batteries. The fluorinated electrolytes, owing to the high electronegativity of fluorine, possesses attractive physicochemical properties, including low melting point, high flash point, and low solubility of lithium polysulfide, and can form a compact and stable solid electrolyte interphase (SEI) with the lithium metal anode. Herein, we review recent advancements in the development of fluorinated electrolytes for use in Li-S batteries. The effect of solvent molecular structure on the performance of Li-S batteries and the formation mechanism of SEI on the cathode and anode sides are analyzed and discussed in detail. The remaining challenges and future perspectives of fluorinated electrolytes for Li-S batteries are also presented. (C) 2019 Science Press and Dalian Institute of Chemical Physics, Chinese Academy of Sciences. Published by Elsevier B.V. and Science Press. All rights reserved.