A Durable and Adaptive Interfacial Ion Rectification Layer Empowering Reversible Zinc Metal in Seawater Batteries

Seawater is an abundant and cost‐free electrolyte source for Zn‐ion batteries, but its high chloride ions (Cl − ) content severely corrodes zinc (Zn) metal anodes. Here, we well resolve this obstacle by designing a binary additive system comprising biomass‐derived 2,5‐furandicarboxylic acid (FDCA) and dimethyl sulfoxide (DMSO) that in situ forms an interfacial ion rectification layer (IIRL) on the Zn anode. DMSO enhances FDCA solubility and cooperatively tunes the Zn 2+ solvation structure into [Zn(H 2 O) 3.74 (DMSO) 0.73 (FDCA) 0.66 ] 2+ to ease desolvation. Additionally, FDCA molecules preferentially adsorb onto the Zn anode surface, creating a negatively charged interface that electrostatically repels Cl − ions and regulates local protons (H + ) to suppress by‑products. This multifunctional IIRL enables unprecedented cycling durability. The Zn//Zn cells achieve exceeding 3400 h (1 mA cm −2 /1 mAh cm −2 ) of stable cycling with simulated seawater electrolyte. Remarkably, in natural seawater, the cells sustain a cumulative plating capacity of 3.5 Ah cm −2 , and the Zn//NaVO full cells retain high capacity and capacity retention over 1000 cycles at 2 A g −1 . This work proposes a viable path to harness seawater for sustainable batteries by designing smart electrolyte interfaces that can selectively regulate ion transport at the electrode.