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Solid electrolytes (SEs) play an essential role in the development of all‐solid‐state batteries (ASSBs) due to their exceptional ionic conductivity. However, conventional pelletized SEs with hundreds of micrometers result in highly reduced energy density and suffer from mechanical brittleness, which delay the commercialization of ASSBs. In this study, we present an innovative approach to fabricate SE membranes with perforated Al2O3 nanolayer‐coated polyethylene (PE) separator as a mechanical supporter. Al2O3‐coated separators exhibit better adhesion with LPSCl particles and better thermal stability. As a result, the SE membrane exhibits thickness of 35 μm while maintaining a superior mechanical tensile strength. Furthermore, when the SE membrane is applied to Li||LiNi0.7Co0.15Mn0.15O2 full‐cells, stable cycling performance over 250 cycles, which is comparable to thick LPSCl pellet cell, can be achieved even with higher conductance (>150 mS). Our results highlight the potential of thin and durable SE membranes in contributing to the commercialization of ASSBs. [ABSTRACT FROM AUTHOR]

Ceramic-coated separators (CCSs) used in lithium-ion batteries (LIBs) play an important role in ensuring the safety of LIBs. However, conventional CCSs fabricated by coating the slurry consisting of ceramic particles and binder have limitations due to the micrometer-thick ceramic coating layer (CCL), compromising the energy density and power capabilities of LIBs. To address this relationship, ultra-thin CCSs fabricated by the sputtering process have attracted attention due to their high thermal stability even with nanometer-thick CCL. Nevertheless, batch-type sputtering machines cannot provide roll-based CCSs for commercial LIBs. Herein, we demonstrate the continuous fabrication of ultra-thin CCS rolls with a pilot-scale direct current (DC) roll-to-roll sputtering process. The ionic conductance and thermal stability are compared with the slurry-based CCS by controlling the coating thickness through the line speed. In addition, the electrochemical performance of the pouch cell (LiNi 0.6 Co 0.2 Mn 0.2 O 2 /graphite, 550 mAh) is evaluated to confirm the applicability of the roll-to-roll sputtered ultra-thin, binder-free CCS (R2R-UB-CCS) to LIBs. Owing to the nanometer-thick CCL, the pouch cell with the R2R-UB-CCS shows higher power capabilities than the bare polyethylene (PE) separator and slurry-based CCS. Thus, the roll-to-roll sputtering process for large-scale, high-speed mass production of ultra-thin CCS has the potential for high safety and high-energy-density LIBs. [Display omitted] • Ultra-thin ceramic-coated separators were fabricated via roll-to-roll sputtering. • A nm-thick ceramic coating layer improves ionic conductance and thermal stability. • Pouch cells with roll-to-roll sputtered CCS shows higher power capabilities. • Thus, roll-to-roll sputtered CCS has the potential to be applied in commercial LIBs. [ABSTRACT FROM AUTHOR]