Selective and Reversible Polysulfide-macrocycle Binding at Modified Membranes Suppress Shuttling in Lithium Sulfur Batteries

Lithium sulfur (LiS) batteries are among the next generation of rechargeable batteries offering high energy densities. Obstacles remain for their practical application, such as capacity fading and low Coulombic efficiency resulting from shuttling and reaction of polysulfides with the Li anode. A new supramolecular approach to suppress shuttling using reversible binding of anionic polysulfides, e.g., S3•–, S62–, S72–, S82–, by anion-selective receptors, called cyanostar (CS) macrocycles is reported. Standard separators were coated with the macrocycles and formed chemically selective membranes. Unlike adsorption materials and non-selective supramolecular approaches, cyanostar provides a well-defined molecule-to-molecule mechanism to capture polysulfides as host-guest complexes like (CS)2•S3•– and (CS)4•S72–. Permselectivity emerges from reversibly binding polysulfides inside the membrane to prevent anions passing while allowing cations to pass. Controls using macrocycles that are not selective for anions do not stop shuttling. Cyanostar-coated membranes turn on charging, reduce capacity fading from 0.51 to 0.36% per cycle and improve Columbic efficiency to 85%. These improvements occur even without addition of lithium nitrate used almost universally to inhibit reactions with the Li anode. This new strategy showcases the benefits of using selective receptors to manage movement of ions in sulfur-based batteries.