High-energy non-aqueous lithium sulfur (Li--S) redox flow batteries are of interest for stationary applications. However, the presence of insoluble short-chain polysulfides largely sacrifices the high energy opportunity due to deposition of Li₂S₂/Li₂S-- onto the current collectors (for example, graphite felt). In addition, the unstable interface between the conventional electrolyte and the lithium metal anode surface also limits the long-term cycling performance of the redox flow batteries.

To address these issues, PNNL researchers have developed a device that improves the long-term performance of high-energy lithium sulfur redox flow batteries.  The device comprises a lithium sulfur redox flow battery with an electrolyte composition containing a dissolved Li₂S_x electroactive salt and a solvent selected from dimethyl sulfoxide, tetrahydrofuran, or a mixture thereof.  The device also includes a supporting salt at a concentration of at least 2 Molar that is measured by moles of supporting salt divided by the volume of the solvent without considering the volume change of the electrolyte after dissolving the supporting salt.