Tannic Acid–Fe 3+ Complex‑Sulfonate Coupled Hydrogel Electrolyte for Stable Zinc Anodes

ABSTRACT Aqueous zinc‐ion batteries feature low cost and inherent safety for large‐scale energy storage. However, their practical deployment is significantly hindered by zinc dendrite proliferation and interfacial corrosion. Conventional electrolytes fail to address cascading failure modes, including corrosion onset, current concentration, and hydrostatic penetration. In this study, we fabricate a high‐performance hydrogel electrolyte membrane via robust electrostatic interactions between tannic acid‐ferric ion complexes and sulfonate groups. This membrane delivers ionic conductivity of (39.94 ± 0.33) mS cm −1 , a high zinc‐ion transference number of (0.91 ± 0.02), and favorable mechanical adaptability. Combined DFT calculations, COMSOL simulations, and multi‐scale characterizations uncover a three‐tier synergistic defense mechanism: tannic acid‐ferric ion Lewis‐acid sites inhibit interfacial corrosion; interconnected sulfonate‐tannic acid‐ferric ion networks realize uniform electric‐field distribution; reversible iron‐oxygen coordination bonds alleviate deposition‐induced internal stress. Symmetric cells sustain stable cycling over 600 h under extreme conditions (65 mA cm −2 , 58.5 mAh cm −2 , 99.7% depth of discharge). Polyaniline‐based full cells achieve 5200 stable cycles with average Coulombic efficiency above 99.9%, and vanadium pentoxide‐based cells exhibit robust cycling performance. This work provides a viable electrolyte strategy for stabilizing zinc anodes and offers valuable insights into high‐performance aqueous metal‐battery electrolyte design.