Finely‐Tuned Polar‐Nonpolar Synergistic Binder Enables Ultra‐Thin Sulfide Solid Electrolyte Membrane for All‐Solid‐State Batteries

Abstract The solid electrolyte (SE) membrane plays a crucial role in sulfide‐based all‐solid‐state batteries (ASSBs). However, the challenge of finding appropriate polymer binders with excellent (electro‐)chemical compatibility and adhesive properties, remains a significant obstacle for wet slurry processing of sulfide SE membranes. Herein, a novel “polar‐nonpolar synergistic” finely‐tuned strategy is employed to design an ethylene‐methyl acrylate (EMA) copolymer binder to facilitate wet‐slurry‐based fabrication of sulfide SE membranes. Significantly, by adjusting the ratio of polar and nonpolar groups, this methodology enables the binder to dissolve effectively in a toluene‐based slurry and also ensures good adhesion between the EMA binder and SE particles. The SE membrane prepared with EMA binder exhibits an ultra‐thin thickness (36 µm), flexibility, and excellent ionic conductivity (1.43 mS cm⁻¹). The ASSB assembled with the SE membrane shows an excellent capacity retention rate of 92.9% after 120 cycles at 0.5 C. This work on the “polar‐nonpolar synergistic” finely‐tuned effect of binder provides insight for manufacturing high‐quality sulfide SE membranes.