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The mechanically and electrochemically stable and ionically conducting solid electrolyte interphase (SEI) is important for the stabilization of metal anodes. Since SEIs are originally absent in aqueous zinc metal batteries (AZMBs), it is very challenging to suppress water‐induced side reactions and dendrite growth of Zn metal anodes (ZMAs). Herein, a gradient‐structured and robust solid gradient SEI, consisting of B,O‐inner and F,O‐exterior layer, in situ formed by hydrated eutectic electrolyte for the homogeneous and reversible Zn deposition, is demonstrated. Moreover, the molar ratio of acetamide to Zn salt is modulated to prohibit the water activity and the hydrolysis of BF4− as well as to achieve high ionic conductivity owing to the regulation of the solvation sheath of Zn2+. Consequently, the eutectic electrolyte allows Zn||Zn symmetric cells to achieve a cycling lifespan of over 4400 h at 0.5 mA cm−2 as well as Zn||PANI full cells to deliver a high capacity retention of 73.2% over 4000 cycles at 1 A g−1 and to demonstrate the stable operation at low temperatures. This work provides the rational design for the hydrated eutectic electrolyte and the corresponding gradient SEIs for dendrite‐free and stable Zn anodes even under harsh conditions. [ABSTRACT FROM AUTHOR]

[Display omitted] • A supramolecular α-CD is employed as additive of zinc sulfate electrolyte. • The preferential adsorption of α-CD suppresses side reactions of Zn anodes. • The α-CD additive induces preferential epitaxial growth of Zn along (0 0 2) plane. • The α-CD additive greatly improves the reversibility of Zn deposition. Recently, aqueous zinc-ion batteries (AZIBs) have received significant attention owing to the high theoretical capacity of zinc metal, high safety, and low cost. However, H 2 O-induced parasitic reactions and uncontrollable dendritic growth on metallic Zn anodes hinder the practical application of AZIBs. Herein, we demonstrate supramolecular α-cyclodextrin (α-CD), which is added to sulfate electrolyte solutions, to regulate the deposition of Zn ions and suppress the formation of the by-product zinc sulfate (Zn 4 SO 4 (OH) 6 ·xH 2 O). The strong affinity of the α-CD additive for the surface of the Zn-metal anodes induces preferential epitaxial growth of Zn along the (0 0 2) plane, which results in achieving the improved reversibility of Zn deposition. Consequently, the addition of α-CD extends the lifespan of symmetric cells beyond 770 h, even at a high current density of 6 mA cm−2 and capacity of 6 mA h cm−2. This study highlights an innovative supramolecular approach for interface regulation of metallic Zn electrodes for advanced rechargeable aqueous batteries. [ABSTRACT FROM AUTHOR]