Process Window Evaluation for Slot Die Coating of PEO‐Based Electrolytes in All‐Solid‐State Batteries

The production of solid electrolytes (SE) for all solid‐state batteries (ASSB) requires thin, homogeneous layers for efficient energy storage. This study optimizes process windows for poly(ethylene oxide) (PEO)‐based coating fluids using the slot die process. A key challenge is adjusting pseudoplastic properties to ensure stable coatings. By varying PEO concentrations (15-25 wt%) and considering film break‐up limits (low‐flow limit, air entrainment), stable coatings are achieved. Critical process parameters, including coating speed, dispense rate, and coating gap, are identified. Unlike previous studies focused on liquid electrolytes, this work highlights the 22 wt% PEO fluid as optimal, balancing capillary and viscous forces (Ca ≈ 1). This challenges the assumption that higher viscosity always improves coating stability, emphasizing the importance of pseudoplastic flow behavior. Ionic conductivities confirm SE suitability for ASSBs. Combining experimental DoE analysis with extended theoretical modeling, this study advances understanding of film break‐up in pseudoplastic systems, setting a benchmark for stable SE coatings.