Lithium-sulfur batteries hold great promise for large-scale energy storage owing to their high theoretical energy density and low cost. However, the insulating nature of sulfur and shuttle effect of polysulfides result in low sulfur utilization and rapid capacity decay. Here, sulfonated graphene is fabricated using the low-cost diluted sulfuric acid as sulfonated reagent, for constructing the freestanding sulfur cathode. It is confirmed that the sulfo groups grafted on graphene serve as mediators to react with long-chain polysulfides by forming the thiosulfate/polythionate intermediates, and facilitate the conversion of long-chain polysulfides into short-chain species and solid discharge products. Crucially, the freestanding cathode with sulfur loading of 8.2 mg cm−2 exhibits an areal capacity of 7.57 mA h cm−2 and stable cycling over 100 cycles at 0.1 C.