Micro‐Stepwise (100) Crystal Face Coupling Molecular‐Layer Engineering Promises High‐Performance Zn‐Iodine Batteries in Wide pH and Seawater Electrolytes

Aqueous zinc–iodine batteries (ZIBs) are promising for large‐scale energy storage but suffer from interfacial challenges in wide pH and seawater electrolytes, such as polyiodide shuttling, chloride‐induced pitting, and dendrite growth. This study proposes the engineering of micro‐stepwise structures with exposed (100) facets via molecular modulation, which guides uniform distribution of zinc species preventing the formation of passivation layers in wide pH electrolytes. Additionally, the molecular layer reduces interfacial H 2 O activity via hydrogen bonds and physically blocks the migration of Cl − and polyiodides towards the anode, alleviating corrosion and pitting within seawater electrolytes. Benefiting from the coupling effect of micro‐stepwise and molecular layers, the Ah‐level Zn||I 2 pouch cells deliver high capacities of 1.13 (2 mA cm −2 ) and 0.61 (4 mA cm −2 ) Ah after 110 and 1000 cycles in acidic electrolytes. The full cells also operate stably in acidic and alkaline electrolytes. It's worth noting that the Zn||I 2 full cell delivers a high capacity of 180 mAh g −1 at 20 A g −1 after 20 000 cycles in seawater electrolyte. This study presents an effective interface engineering strategy for balancing long‐term stability with rapid electrochemical reaction kinetics of ZIBs under diverse electrolyte scenarios.