CIS's continuous-process pilot line for sulfide-based solid electrolyte at its Daegu Plant 3 (2–5 t/year, expanded from the existing batch process's 840 kg) and M Plus's order for six types of all-solid-state battery assembly equipment (targeting development/fabrication completion by end-2026) reveal a textbook interface problem: the production capacities of the upstream materials process and the downstream assembly process are not scaled up on the same timeline. This article estimates, as an assumed scenario, the buffer stock and takt-time loss required between these two processes, to quantitatively pin down why the materials-assembly interface design is a leading variable for the line's overall OEE (Overall Equipment Effectiveness). The downstream assembly equipment's target…