Coupling Water‐Poor Electric Double Layer with Stable Organic–Inorganic SEI via Large‐Steric‐Hinderance Electrolyte Additive for Highly Reversible Zinc Anodes

ABSTRACT The performance of aqueous zinc‐ion batteries is limited by parasitic reactions and dendrite growth, originating from a H 2 O‐rich electric double layer (EDL) and the disordered diffusion of Zn 2+ at the Zn anode/aqueous interface. This study proposes a steric‐hindrance‐driven interfacial engineering strategy, using sulfonate‐based additives with various molecular sizes in ZnSO 4 electrolytes. Combined experimental and theoretical analyses reveal that sodium diphenylamine‐4‐sulfonate (SDPS) with large steric hindrance effect spontaneously adsorbs onto the Zn anode, establishing a H 2 O‐poor EDL while reconstructing the anion‐rich solvation structure and the hydrogen‐bond network. This reconfigured interface further facilitates the in situ formation of an organic–inorganic hybrid solid electrolyte interphase (SEI) through the SDPS and SO 4 2− decomposition. Consequently, an interface, comprising an SDPS adsorption shield, a carbon‐rich organic phase, and a sulfur‐rich (ZnS‐dominated) inorganic phase, is achieved, which collectively suppresses H 2 O‐induced parasitic reactions and inhibits dendrite growth. The Zn||Zn symmetric cell with the SDPS‐containing ZnSO 4 electrolyte exhibits prolonged cycling capabilities exceeding 1400 h at 20 mA cm −2 , and maintains stable operation for 570 h under a high depth of discharge of 95.7%. By correlating molecular steric hinderance with the co‐evolution of the EDL and SEI, this work provides new insights for designing electrolyte additives for advanced aqueous batteries.