Synergistic Dual‐Interface Engineering of Anode and Cathode Enabling High‐Performance Seawater‐Based Zn–Halogen Batteries

ABSTRACT Seawater zinc‐halogen batteries (SZHBs) are affected by water‐related side reactions and Cl − pitting corrosion on the anode, while problems arise from polyhaline species shuttle, sluggish kinetics, and I + hydrolysis on the cathode. Herein, a dual‐interface modification strategy is proposed to regulate the microenvironment of the cathode and anode, improving the electrochemical performance of SZHBs. At the anode, the formation of an organic–inorganic hybrid solid electrolyte interphase prevents water and Cl − from contacting the electrode while ensuring uniform deposition of Zn 2+ . At the cathode, the shuttling and conversion behaviours of I 3 − are modulated by electrostatic forces introduced via additives acting on I 3 − . Lewis base sites and multi‐site hydrogen bonds simultaneously regulate the activity of I + and water, inhibiting the hydrolysis of I + . Improving the stability of dual‐interface enables Zn||I 2 pouch cells to maintain the high average capacity of 1.545 Ah after 250 cycles with a high energy density of 249 Wh kg −1 based on cathode material in the modified aqueous electrolyte, and run 120 cycles in the modified seawater electrolyte. The electrochemical performance of Zn‐bromine batteries is significantly enhanced in a modified seawater electrolyte. This study achieved Ah‐level SZHBs pouch cells, opening a new pathway toward the practical application of seawater batteries.