High Energy Density Solid-State Lithium–Sulfur Batteries: Challenges and Advances in Cathode Materials

All-solid-state lithium–sulfur batteries (ASSLSBs), as an energy storage system for achieving the high energy density target of 600 Wh kg–1, hold significant importance in driving in next-generation battery technologies. This review focuses on the key challenges of cathode materials for high energy density ASSLSBs and systematically summarizes the recent research progress. First, the interfacial reaction mechanisms among active materials, conductive agents, and solid electrolytes in sulfur cathodes are analyzed in depth, revealing the fundamental causes of interface failure. Second, the advancements in composite cathodes are summarized, including the influence of preparation processes, material design strategies, and the structure-performance regulation mechanisms of mixed conductors. Next, the role of interface engineering strategies in enhancing reaction kinetics is discussed in detail. Furthermore, recently developed solutions for critical technical bottlenecks, such as high sulfur loading and low-temperature adaptability, are reviewed. Finally, future research directions are envisioned from the dimensions of multiscale interface engineering, material systems, and characterization techniques. This review aims to move beyond conventional single-component optimization approaches, developing a multicomponent framework for cathode design. The review further provides references for developing high-energy-density, long-cycle-life ASSLSBs, offering a comprehensive reference for advancing the practical application of this energy storage technology.