From Powder to Sheets: A Comparative Electrolyte Study for Slurry-Based Processed Solid Electrolyte/Binder-Sheets as Separators in All-Solid-State Batteries

A key for the market penetration of large-scale and high energy All-Solid-State Batteries (ASSBs) are sheet-type cell components. Herein, we report a slurry-based process to obtain free-standing solid electrolyte (SE)/binder composite sheets as ASSB separators. We investigate three different sulfidic solid electrolyte systems (Li₆PS₅Cl, Li₇P₃S₁₁ and Li₁₀SnP₂S₁₂) in combination with a hydrogenated nitrile butadiene rubber (HNBR). By means of electrochemical impedance spectroscopy (EIS), the influence of separator composition and processing on the ionic sheet conductivity is evaluated. Independent of the solid electrolyte material, a reduction by a factor of three compared to the pristine powder conductivity at 70 MPa operation pressure and by a factor of eight compared to the maximum powder conductivity is observed. This can be attributed to the addition of the ionically isolating binder, which however is necessary for the production of freestanding sheets. We show the beneficial effect of pre-compressing the sheets to little porosity values on the apparent sheet conductivity. Lastly, we investigate and decouple the influence of fabrication and operating cell pressure on the produced separator sheets.