Solid-State Electrolytes for Lithium-Ion Batteries: Mechanisms, Interfaces, Challenges, and Future Perspectives

Solid-state electrolytes (SSEs) mark a transforming path toward high-energy-density and intrinsically safe Li-ion batteries. This review systematically summarizes the mechanisms, classifications, interfacial challenges, and industrialization prospects of SSEs. The ion transport behavior is discussed in the context of inorganic, polymeric, and composite electrolytes, focusing on the decisive role that structural factors play for Li migration. The most relevant interfacial issues are specifically discussed, including chemical incompatibility, space-charge layers, and dendrite penetration, and their solution strategies, such as interface coatings, artificial SEIs, and mechanical optimization. Finally, conclusive industrial outlooks are provided by evaluating scalable synthesis, processability, and compatibility with traditional roll-to-roll manufacturing. Future directions underpin the conclusive importance of multi-ion and hybrid electrolyte systems together with sustainable recycling and integrated safety management. These synergistic advancements are expected to accelerate the transition from laboratory-scale research to industrial realization of safe, durable, and high-performance all-solid-state lithium-metal batteries.