Mechanistic Progress and Challenges for Carbon‐Based Protective Interlayer/Separator Modification for the Practical Development of Next‐Generation Alkali Metal–Sulfur Batteries

Alkali metal–sulfur batteries (AMSBs) are promising for next‐generation energy storage, offering much higher energy density than lithium‐ion batteries. However, commercialization faces challenges like sulfur's insulating nature, volume expansion, and the polysulfide shuttle effect, which causes poor cycle life, low efficiency, and active material loss. While conductive, porous sulfur hosts help with insulation and volume changes, polysulfide shuttling remains a major issue. A practical solution is adding an interlayer between the cathode and separator, which acts as a physical barrier, an upper current collector, and a polysulfide reservoir, improving electrochemical performance. Though well‐studied in lithium‐sulfur batteries, interlayers have received less attention in broader AMSB chemistries. This review examines interlayer roles, fabrication methods, and mechanisms in AMSBs, offering insights into material selection based on different cathode chemistries. Potential limitations in cell assembly are also discussed, and guidelines for optimizing interlayer design are provided. Drawing from our AMSB experience, this study aims to highlight strategies to enhance battery performance. This study hopes this mini‐review contributes to advancing AMSBs, paving the way for next‐generation battery technologies.