Carbon-Nitride-Based Materials for Advanced Lithium–Sulfur Batteries

Lithium–sulfur (Li–S) batteries are promising candidates for next-generation energy storage systems owing to their high energy density and low cost. However, critical challenges including severe shuttling of lithium polysulfides (LiPSs) and sluggish redox kinetics limit the practical application of Li–S batteries. Carbon nitrides (C_xN_y), represented by graphitic carbon nitride (g-C₃N₄), provide new opportunities for overcoming these challenges. With a graphene-like structure and high pyridinic-N content, g-C₃N₄ can effectively immobilize LiPSs and enhance the redox kinetics of S species. In addition, its structure and properties including electronic conductivity and catalytic activity can be regulated by simple methods that facilitate its application in Li–S batteries. Here, the recent progress of applying C_xN_y-based materials including the optimized g-C₃N₄, g-C₃N₄-based composites, and other novel C_xN_y materials is systematically reviewed in Li–S batteries, with a focus on the structure–activity relationship. The limitations of existing C_xN_y-based materials are identified, and the perspectives on the rational design of advanced C_xN_y-based materials are provided for high-performance Li–S batteries.