Tailoring Alkyl Chain Length to Customize Dual-Electrode Interface for Reversible Four-Electron Iodine Chemistry in...

Aqueous zinc-iodine (Zn-I₂) batteries show great promise for large-scale energy storage, yet realizing four-electron transfer for high energy density requires cooperation between zinc interface regulation and high valence iodine anchoring. Herein, the dual-electrode interface microenvironment is customized via a series of bromide quaternary ammonium salts with varied alkyl chain length. The moderately-sized tetraethylammonium bromide (TEAB) constructs a well-ordered electric double layer that suppresses water penetration and hydrogen evolution while promoting uniform Zn²⁺ deposition. Simultaneously, TEAB stabilizes I⁺ through a synergistic coordination-hydrophobic anchoring mechanism, preventing iodine hydrolysis and shuttling. This synergistic customization of the anode-cathode dual-interface microenvironment successfully activates the reversible four-electron I^-/I⁺ redox chemistry. With this design, the symmetric Zn cell operates stably for over 50 days at 5 mA cm^-2 and 5 mAh cm^-2 as well as shows wide-temperature adaptability from -20°C to 50°C, the full cell retains 84.5% capacity after 8000 cycles at 1 A g^-1, and an Ah-scale pouch cell delivers stable 428 cycles with a high-capacity retention of 98.74% even under a heavy iodine loading of 20 mg cm^-2. This work establishes a molecular-level design paradigm for simultaneous anode and cathode interface engineering, advancing practical high-energy aqueous zinc-iodine batteries.