A Self-Limited Free-Standing Sulfide Electrolyte Thin Film for All-Solid-State Lithium Metal Batteries

All-solid-state (ASS) lithium metal batteries (LMBs) are considered the most promising next-generation batteries due to their superior safety and high projected energy density. To access the practically desired high energy density of ASS LMBs, an ultrathin solid-state electrolyte (SSE) film with fast ion-transport capability presents as an irreplaceable component to reduce the proportion of inactive materials in ASS batteries. In this contribution, an ultrathin (60 µm), flexible, and free-standing argyrodite (Li₆PS₅Cl) SSE film is designed through a self-limited strategy. A chemically compatible cellulose membrane is employed as the self-limiting skeleton that not only defined the thinness of the sulfide SSE film but also strengthened its mechanical properties. The ionic conductivity of the SSE film reaches up to 6.3 × 10⁻³ S cm⁻¹ at room temperature, enabling rapid lithium-ion transportation. The self-limited SSE thin films are evaluated in various ASS LMBs with different types of cathode (sulfur and lithium titanate) and anode materials (lithium and lithium-indium alloy) at both mold-cell and pouch-cell levels, demonstrating a stable performance and high-rate capability. This study provides a general strategy for the rational design of an SSE thin film towards high-energy-density ASS batteries.