All-Solid-State Batteries In article number 2502996, Young-Gi Lee, Yong Min Lee, and co-workers fabricated a scalable scaffold-supported solid electrolyte separator (SES) with a thickness of 27 μm and high ionic conductance via laser drilling and tape casting. Mechanical and multiphysics simulations guide the design of the porous scaffold. The SES enables high cell-level energy density of 322 Wh kg−1 and excellent mechanical durability, supporting roll-to-roll (R2R) processing for practical all-solid-state batteries.