Effectiveness of dioxolane/dimethoxyethane mixed solvent for the fabrication of lithium-sulfur semiflow batteries

In order to implement a Li/S semiflow battery, a mixture of lithium polysulfide (Li2S8) dissolved in dioxolane/dimethoxyethane was studied as a catholyte in Li/carbon battery cells. The Li2S8 polysulfide was prepared by stirring Li2S and elemental sulfur in a 1:1 mixture of dioxolane/dimethoxyethane heated at 80 °C. The mixture of polysulfides was tested in a lithium metal cell. The working electrode was a mixture of Ketjenblack carbon (used as conductive filler) and PTFE. It was found the Li2S8 polysulfide immediately converts into Li2S4 and sulfur when added to the electrolyte solution. The electrochemical tests showed that the cell retains excellent Coulombic efficiency and good cycling stability. The potential window used during the electrochemical tests plays an important role on the cell performance in terms of stability and capacity. An improvement of more than 500 mAh g−1 in the specific capacity retention was observed when the potential window was reduced from 3.0-1.5 V to 2.8-1.7 V. Post mortem SEM and EDS analyses confirmed that not only the surface but the whole of the working electrode participates to the electrochemical reaction.