A Bilayered Inorganic‐Metal Interface Enables Highly Reversible Aluminum Deposition for Long‐Life Aqueous Batteries

ABSTRACT Rechargeable aqueous aluminum metal batteries (AAMBs) represent a promising large‐scale energy storage technology due to their unique advantages of high volumetric energy density, low cost, and operational safety. However, their cyclic stability and Coulombic efficiency are constrained by the sluggish interfacial kinetics originating from the stable [Al(H 2 O) 6 ] 3+ complex, which leads to rigorous issues such as hydrogen evolution reaction and surface passivation. Herein, a gradient Sn/SnO x synergistic interfacial layer with high aluminophilicity and ion‐buffering capability (termed as HAIBSL) was integrated on metallic Al anode by one‐step chemical displacement reaction, applicable also to Cu/CuO x and Cd/CdO x interphases. As a prototype, Sn/SnO x layer not only accelerates Al 3+ desolvation kinetics and uniform plating, but also acts as a barrier to avoid water‐induced side reactions, as confirmed by electrochemical and theoretical experiments. Moreover, X‐ray diffraction (XRD) and time‐of‐flight secondary ion mass spectrometry (TOF‐SIMS) confirm the excellent cycling stability of this layer. Consequently, the symmetrical HAIBSL@Al cell demonstrates ultrastable cycling with a low overpotential for 1800 h at 0.05 mA cm −2 . Moreover, the HAIBSL@Al can be compatible with multiple cathodes and exhibits a cycling life of 700 cycles with potassium cobalt hexacyanoferrate (II) cathode, underscoring the gradient synergistic interfacial layer as a robust and versatile strategy for AAMBs.