A composite separator with a thin-film polysulfide trap is developed for lithium-sulfur batteries. A polyethylene glycol-supported microporous carbon coating (MPC/PEG coating) on a Celgard separator suppresses polysulfide diffusion through its physical and chemical polysulfide-trapping capabilities. The MPC/PEG-coated separator thus facilitates the use of pure sulfur cathodes that generally suffer from poor cyclability and low electrochemical utilization.