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

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 Zn²⁺. At the cathode, the shuttling and conversion behaviours of I₃ ⁻ are modulated by electrostatic forces introduced via additives acting on I₃ ⁻. 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||I₂ 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.