Emerging medium- and high-entropy materials as catalysts for lithium-sulfur batteries

Lithium–sulfur batteries (LSBs) have attracted significant attention as a promising next-generation energy storage system due to their high theoretical energy density, low cost, and environmental friendliness. However, the practical implementation of LSBs faces several fundamental challenges, including the rapid capacity decay and poor cycling stability resulting from the dissolution of lithium polysulfides (LiPSs) during cycling, as well as security issues arising from the flammability of ether-based liquid electrolytes. In recent years, significant progress has been achieved in overcoming those drawbacks through the use of catalysts which play a crucial role by promoting the redox reactions and suppressing the shuttle effect. Among the main trends, the concept of medium and high entropy materials (MEMs and HEMs) has emerged as a novel approach for designing advanced functional catalysts, making them suitable multimetallic-based candidates for LSBs. This review focuses on the development and utilization of MEMs and HEMs (alloys, metal oxides, Prussian blue analogues, metal sulfides, metal phosphides, and MXenes) as both sulfur hosts and catalysts for LSBs. The roles of various elements and their synergistic effects on the electrochemical performance are discussed, along with the strategies to optimize the catalyst design for enhanced sulfur utilization and cycling stability. Furthermore, the challenges, future perspectives, and directions in designing MEMs and HEMs-based catalysts for developing high-performance and reliable LSBs are addressed, paving the way for future energy storage applications.