In this new issue of Joule, Xianfeng Li and colleagues demonstrated the pilot scale roll-to-roll synthesis of sulfonated poly(ether ether ketone) (SPEEK) membrane and the scaling up of zinc flow batteries (ZFBs) stack 300–4000 W with membrane area up to 3 m2. Compared to expensive Nafion membranes ($500–1500 m−2), cost analysis demonstrated the significant cost reduction of SPEEK membranes to $12 m−2 and subsequently enormous cost reduction of flow battery stacks. This cost reduction will advance the manufacturing of flow battery systems for large-scale energy storage plants.1