Integrated Electrode‐to‐Device Design via Combination of Grain Boundary Reconstruction and Dynamic Gas Management Toward Stable 3 Ah Aqueous Zinc‐Iodine Pouch Cells

The substantial electrochemical performance gap between Ah‐level pouch cells and laboratory‐scale coin cells remains a critical bottleneck hindering the practical application of aqueous Zn‐I 2 batteries. Herein, Zn anode degradation and cell‐level gas accumulation, exacerbated under large‐area‐electrode conditions, are systematically identified as dominant failure mechanisms in high‐capacity Zn‐I 2 pouch cells. Accordingly, an integrated electrode‐to‐device strategy is proposed, combining Zn grain‐boundary reconstruction with dynamic gas management. The intrinsically nonuniform grain boundary distribution in commercial zinc foil is confirmed to induce stripping heterogeneity and subsequent dendrite growth, while persistent H 2 evolution leads to cell swelling and electrolyte leakage, ultimately resulting in accelerated capacity fading. At the electrode level, a scalable electrodeposition strategy yields current‐collector‐integrated zinc anodes with refined grains and homogenized boundaries, effectively mitigating initial stripping heterogeneity and enhancing zinc utilization. At the device level, a selective H 2 ‐expulsion window (LaNi‐based hydrogen storage alloy nanoparticles embedded in a hydrophobic PTFE matrix) is integrated into the aluminum‐plastic packaging, enabling efficient H 2 removal while blocking water vapor to maintain electrolyte stability. Leveraging this design, multilayer‐stacked Zn‐I 2 pouch cells with >3 Ah capacity and an ultra‐low N/P ratio of 1.18 achieve over 600 stable cycles. This work offers a scalable, system‐level solution toward practical aqueous Zn‐based pouch cells.