Abstract: Described herein are methods and systems for forming electrode stacks. For example, a method may comprise applying in-plane tension to a separator sheet and inspecting the separator sheet while applying the in-plane tension. This under-tension allows identifying any defects on the separator sheets that are not curable by tension, e.g., permanent wrinkles, tears, contaminants, and the like. Furthermore, this in-plane tension can be used for stacking and maintained while an electrode is placed over the separator. The tension can be formed by positioning vacuum clamps along the opposite edges (e.g., long edges) of the separator sheet. For example, one vacuum clamp can extend along the entire separator edge. Alternatively, multiple clamps can be distributed along the edge. Furthermore, additional clamps can be positioned along the remaining two edges (of the rectangular separator sheet). The vacuum clamps can move in various directions and/or rotate to apply the in-plane tension.