Anion Engineering of Sulfide Solid Electrolytes: From Fundamentals to High-Performance All-Solid-State Batteries

Sulfide-based solid-state electrolytes (SSSEs) have emerged as one of the most promising materials for next-generation all-solid-state batteries (ASSBs), owing to their high ionic conductivity, favorable mechanical properties, and compatibility with high-energy-density electrode materials. This review presents a comprehensive overview of recent advancements in the anion engineering of SSSEs, with a focus on the central role of the anionic sublattice in governing lithium-ion transport. We discussed the structural families of sulfide electrolytes, elucidated the mechanisms of lithium-ion conduction, and examined how anion disorder and polarizability influence conduction pathways and activation energies. The primary focus of this review was on strategies involving anion substitution and modification, including single- and multi-element doping, multi-anion frameworks, and heterostructure designs, and their effects on electrochemical stability, interfacial compatibility, and mechanical properties. We further reviewed the electrochemical performance metrics, scalability, and processing challenges associated with these materials. Finally, we outlined current limitations and future perspectives on a roadmap toward commercial implementation, highlighting the potential of anion-engineered SSSEs to enable safe, high-performance, and sustainable energy storage in next-generation lithium-ion batteries.