Thin Free-Standing Sulfide/Halide Bilayer Electrolytes for Solid-State Batteries Using Slurry Processing and Lamination

Thin-film solid electrolytes with wide electrochemical stability windows are required to develop solid-state lithium (Li) metal batteries with high energy densities. In this work, free-standing Li₃InCl₆ (30 μm)|Li₆PS₅Cl (30 μm) bilayer thin films are prepared by slurry casting, drying, and lamination. This combination of solid electrolytes is stable at both the cathode interface (high voltages) and anode interface (low voltages). The bilayer thin films exhibit >10× lower area-specific resistance than thick (∼1 mm) pellets fabricated by traditional powder pressing. The free-standing bilayer electrolytes are laminated onto electrodeposited LiCoO₂ cathodes. Subsequently a Li-In anode is laminated on top of the stack, and stable cycling of all-solid-state batteries is demonstrated. Because of reduced ohmic losses, cells fabricated with thin-film electrolytes exhibit lower cell polarization and improved rate capability compared with cells with a traditional pellet geometry. This study offers a general strategy to fabricate free-standing bilayer thin-film solid electrolytes for high-energy-density solid-state batteries.