The impact of THF in ether-based electrolytes for lithium-sulfur battery

Lithium-sulfur (Li/S) batteries using tetrahydrofuran (THF) as an electrolyte solvent have high discharge capacity. In this study, we investigate the effect of THF as an electrolyte solvent on the performance of Li/S batteries. Charge/discharge tests show that Li/S batteries employing THF as an electrolyte solvent have higher discharge specific capacity than those employing 1,3-dioxolane (DOL) and 1,2-dimethyl ether (DME) at low current densities. The reaction rate of S with Li metal and the shuttle effect of polysulfide ions is lower in THF than in DME. Compared to DME and DOL, THF has a higher dielectric constant, and its solvation ability is weaker than that of DME, which is more conducive to the deposition of lithium ions. Electrochemical impedance spectroscopy shows that the charge transfer resistance of symmetric Li metal batteries in THF is lower than that in DOL/DME. THF forms a gel layer that restrains the shuttle effect during battery discharge and increases battery impedance. The addition of DOL to THF can effectively inhibit the formation of a gel layer and improve the coulombic efficiency of the system. Finally, ternary mixed solvents are prepared, and batteries with the new electrolyte solvent reveal better discharge capacity and higher coulombic efficiency than those with the original solvents. Taking the results together, THF appears to be a promising solvent for Li/S batteries.