Understanding the Effect of a Fluorinated Ether on the Performance of Lithium–Sulfur Batteries

A high performance Li-S battery with novel fluoroether-based electrolyte was reported. The fluorinated electrolyte prevents the polysulfide shuttling effect and improves the Coulombic efficiency and capacity retention of the Li-S battery. Reversible redox reaction of the sulfur electrode in the presence of fluoroether TTE was systematically investigated. Electrochemical tests and post-test analysis using HPLC, XPS, and SEM/EDS were performed to examine the electrode and the electrolyte after cycling. The results demonstrate that TTE as a cosolvent mitigates polysulfide dissolution and promotes conversion kinetics from polysulfides to Li2S/Li2S2. Furthermore, TTE participates in a redox reaction on both electrodes, forming a solid electrolyte interphase (SEI) which further prevents parasitic reactions and thus improves the utilization of the active material.