A polymer organosulfur redox mediator for high-performance lithium-sulfur batteries

Commercial application of lithium-sulfur batteries (LSBs) largely depends on precise regulation of complex sulfur redox reactions. Herein, polymer organosulfur compounds (POCs) are designed as promising redox mediators for the first time. The mesoporous yolk-shell POCs with covalently linked short-chain sulfur are coated on commercial PP separators to regulate the redox behavior of sulfur. The short-chain sulfur could spontaneously interact with polysulfides to reversibly regulate the electrochemical conversions of polysulfides, afford faster sulfur redox kinetics and improve the deposition of Li2S. POCs could also interact with lithium ions to stabilize the lithium-metal anode. Hence, the POC endows the commercial sulfur cathode with an outstanding rate performance of 790 mA h g−1 at 4.0 C and a higher capacity retention up to 87% within 1000 cycles at 2.0 C. The LSB with a high-sulfur-loading of 6.8 mg cm−2 and a small electrolyte/sulfur ratio of 5.6 uL mg[S]−1 is also synthesized, achieving an excellent capacity of 5.9 mA h cm−2 after cycling.