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

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.