On the Way Toward Understanding Solution Chemistry of Lithium Polysulfides for High Energy Li–S Redox Flow Batteries

Lithium–sulfur (Li–S) redox flow battery (RFB) is a promising candidate for high energy large‐scale energy storage application due to good solubility of long‐chain polysulfide species and low cost of sulfur. Here, the fundamental understanding and control of lithium polysulfide chemistry are studied to enable the development of liquid phase Li–S redox flow prototype cells. These differ significantly from conventional static Li–S batteries targeting for vehicle electrification. A high solubility of the different lithium polysulfides generated at different depths of discharge and states of charge is required for a flow battery in order to take full advantage of the multiple electron transitions. A new dimethyl sulfoxide based electrolyte is proposed for Li–S RFBs, which not only enables the high solubility of lithium polysulfide species, especially for the short‐chain species, but also results in excellent cycling with a high Coulombic efficiency. The challenges and opportunities for the Li–S redox flow concept have also been discussed in depth.