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 extreme 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. 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 (&lt;50 µm), high ionic conductivity (&gt;1.0 mS cm−1), high robustness, excellent stability. The excellent compatibility among ethyl cellulose, Li6PS5Cl, and toluene is comprehensively studied. Li6PS5Cl shows a high ionic conductivity of 1.6 mS cm-1 and good stability in nonpolar solvent toluene. However, the dispersion of Li6PS5Cl was poor in toluene bringing challenges in film fabrication. The hydrophobic ethyl groups enable ethyl cellulose good solubility in toluene, and the hydrophilic hydroxyl groups helps the Li6PS5Cl dispersing well in toluene. Meanwhile, the point glue effect of the ethyl cellulose has been successfully proved through the X-ray computed tomography. The Li6PS5Cl takes the main fraction of the SE membrane and forms an integrated region, benefiting the ion conduction. The ethyl cellulose randomly distributes at the boundaries of Li6PS5Cl particles but not fully wrapping the particles contributing to less barrier and more continuous ion transport paths. The ASLB utilizing this thin SE membrane delivers outstanding energy densities of 325 Wh kg-1 and 861 Wh L-1 based on cathode and SE layer, and cell-level energy densities of 175 Wh kg-1 and 670 Wh L-1.

Amphipathic bio-based polymer integrating highly ion-conductive membrane for cell-level high energy density all-solid-state batteries

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