Effects of Liquid Electrolytes on the Charge-Discharge Performance of Rechargeable Lithium/Sulfur Batteries: Electrochemical and in-Situ X-ray Absorption Spectroscopic Studies

A sulfur/carbon composite has been prepared to serve as a cathode for lithium/sulfur batteries. The effects of seven different liquid electrolytes on the electrochemical performance were investigated using galvanostatic discharge-charge tests on coin cells. The electrolytes included ether, sulfone, and carbonate solvents with common lithium salts. It was found that the solvent plays a key role on the electrochemical performance of the lithium/sulfur battery cathode while the lithium salt has no significant effects. Additional characterization, using in situ sulfur K-edge X-ray absorption spectroscopy (XAS), provided insights into the soluble sulfur species in the discharged and charged batteries. We find that the use of low-viscosity ethereal solvents results in a more complete reduction of soluble polysulfides, while soluble polysulfides remained more oxidized in viscous ethereal solvents. Moreover, XAS revealed that reduced sulfur species chemically react with carbonate-based solvents, making this class of solvents inappropriate for elemental sulfur cathodes of lithium batteries.