Covalent Confinement of Sulfur Copolymers onto Graphene Sheets Affords Ultrastable Lithium–Sulfur Batteries with Fast Cathode Kinetics

Lithium–sulfur (Li–S) batteries have received significant attention due to the high theoretical specific capacity of sulfur (1675 mA h g–1). However, the practical applications are often handicapped by sluggish electrochemical kinetics and the “shuttle effect” of electrochemical intermediate polysulfides. Herein, we propose an in-situ copolymerization strategy for covalently confining a sulfur-containing copolymer onto reduced graphene oxide (RGO) to overcome the aforementioned challenges. The copolymerization was performed by heating elemental sulfur and isopropenylphenyl-functionalized RGO to afford a sulfur-containing copolymer, that is, RGO-g-poly(S-r-IDBI), which is featured by a high sulfur content and uniform distribution of the poly(S-r-IDBI) on RGO sheets. The covalent confinement of poly(S-r-IDBI) onto RGO sheets not only enhances the Li+ diffusion coefficients by nearly 1 order of magnitude, but also improves the mechanical properties of the cathodes and suppresses the shuttle effect of polysulfides. As a result, the RGO-g-poly(S-r-IDBI) cathode exhibits an enhanced sulfur utilization rate (10% higher than that of an elemental sulfur cathode at 0.1C), an improved rate capacity (688 mA h g–1 for the RGO-g-poly(S-r-IDBI) cathode vs 400 mA h g–1 for an elemental sulfur cathode at 1C), and a high cycling stability (a capacity decay of 0.021% per cycle, less than one-tenth of that measured for an elemental sulfur cathode).