Status and prospects in sulfur-carbon composites as cathode materials for rechargeable lithium-sulfur batteries

Sulfur stands as a very promising cathode candidate for the next-generation rechargeable batteries due to its high energy density, natural abundance, low cost and environmental friendliness. However, the application of lithium-sulfur batteries suffers from low sulfur utilization and poor cycle life of the sulfur cathode. The problems are mainly ascribed to the electrically insulating nature of sulfur and the discharge products, and to the dissolution of the reaction intermediates of polysulfides. Among various approaches, fabricating sulfur-carbon composite cathodes with sulfur embedded within conductive carbon frameworks has been proven promising. Carbon materials, including nanoporous carbon, carbon nanotubes, graphene nanosheets and some other forms, have excellent conductivity, robust chemistry, good mechanical stability, and great abundance. By constraining sulfur within carbon frameworks, the conductivity of the sulfur electrode can be greatly enhanced, and the dissoluble loss of intermediate sulfur species in the liquid electrolyte can also be restrained due to the sorption properties of carbon, leading to a much improved electrochemical performance. This review summarizes the progresses in the sulfur-carbon composite cathodes for lithium-sulfur batteries in recent years, and introduces the roles and the effectiveness of various carbon structures on the electrochemical properties.