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

Sulfide solid-state electrolytes (SEs) featured with nonflammability and superior ionic conductivity (&gt;10-3 S cm-1) enable all-solid-state lithium batteries (ASLBs) to deliver safer and more reliable energy storage. However, current sulfides-based ASLBs exhibit far below expected energy densities at the cell level (&lt;50 Wh kg-1, &lt;100 Wh L-1), due to the employment of SE membranes with high thickness (&gt;500 μm), large weight (&gt;80 mg cm-2), and limited ion conductance. The high sensitivity to polar solvent and natural brittleness of sulfide SE challenge the fabrication of thin light-weight SE membranes with no sacrifice in ionic conductivity.<br/>The binder-assisted solution method is a promising strategy to fabricate a thin and robust sulfide SE membrane. A critical step to is to select a binder satisfying following requirements: 1) Excellent solubility and stability in nonpolar solvent; 2) High stability with sulfide SE; 3) High thermal stability; 4) High binding strength. In this work, for the first time, we employed and studied ethyl cellulose as a binder. Attributing to ethyl cellulose’s unique amphipathic molecular structure, the obtained freestanding SE membrane possesses ultralow thickness, high ionic conductivity, high robustness, good flexibility. The ASLB employing this thin SE membrane delivers exceedingly high energy densities at the cell level.