Amphipathic Binder Integrating Ultrathin and Highly Ion‐Conductive Sulfide Membrane for Cell‐Level High‐Energy‐Density All‐Solid‐State Batteries

Current sulfide solid-state electrolyte (SE) membranes utilized in all-solid-state lithium batteries (ASLBs) have a high thickness (0.5-1.0 mm) and low ion conductance (<25 mS), which limit the cell-level energy and power densities. Based on ethyl cellulose's unique amphipathic molecular structure, superior thermal stability, and excellent binding capability, this work fabricates a freestanding SE membrane with an ultralow thickness of 47 µm. With ethyl cellulose as an effective disperser and a binder, the Li₆ PS₅ Cl is uniformly dispersed in toluene and possesses superior film formability. In addition, an ultralow areal resistance of 4.32 Ω cm^-2 and a remarkable ion conductance of 291 mS (one order higher than the state-of-the-art sulfide SE membrane) are achieved. The ASLBs assembled with this SE membrane deliver cell-level high gravimetric and volumetric energy densities of 175 Wh kg^-1 and 675 Wh L^-1 , individually.