Inhibiting Polysulfide Shuttling with a Graphene Composite Separator for Highly Robust Lithium-Sulfur Batteries

Lithium-sulfur (Li-S) batteries are of considerable interest for high-density energy storage. However, the adoption of Li-S batteries to date has been severely plagued by the polysulfide shuttling effect, whereby polysulfide molecules dissolve into the electrolyte and shuttle across the separator to react with the anode materials, leading to a rapidly fading capacity. Herein, by directly coating a thin layer of reduced graphene oxide (rGO)/sodium lignosulfonate (SL) composite on the standard polypropylene (PP) separator, we produce a rGO@SL/PP separator with abundant negatively charged sulfonic groups in the porous lignin network, which effectively suppress the translocation of the negatively charged polysulfide (PS) ions without compromising the transport of positively charged Li⁺ ions. Using the rGO@SL/PP separator, we demonstrate a highly robust Li-S battery with a capacity retention of 74% over 1,000 cycles. This study defines an effective strategy to inhibit the PS shuttling effect for highly robust Li-S batteries. High-density energy storage is critical for many technologies. Li-S batteries are of particular interest for their high theoretical capacity up to 1,675 mAh g⁻¹. However, the Li-S battery today is seriously plagued by that polysulfide shuttling effect, thich can lead to rapid capacity fading, preventing long-term stable operation for commercial deployment. Here we report the design of a negatively charged graphene composite separator for effective suppression of the polysulfide shuttling effect, whereby a negatively charged 3D porous structure effectively inhibits the translocation of negatively charged polysulfide ions to enable highly robust Li-S batteries. Such a separator may be easily integrated into other optimized devices by simply replacing the traditional separators with the newly designed separators without modifying the electrode structure, and thus may be readily implemented with the most advanced developments in the field to exert a rapid impact on practical technologies. A graphene composite separator with abundant sulfonic groups is prepared by directly polymerizing hexamethylene diisocyanate with reduced graphene oxides and sodium lignosulfonates, followed by a simple filtration process. The rich negative charge in the composite separator effectively suppresses the translocation of the negatively charged polysulfide ions to enable highly robust lithium-sulfur batteries.