A Ternary Electrolyte Enabled Spatially Bulk‐Interface Coupled Regulation for Stable Aqueous Al Metal Batteries

ABSTRACT Aqueous aluminum‐ion batteries are critically hindered by severe interfacial instability and parasitic hydrogen evolution reactions (HER), originating from the highly polarized hydration shell of Al 3+ . To bridge the inherent disconnect between bulk and interfacial dynamics, we propose a spatially bulk‐interface coupled regulation strategy using a multifunctional ternary electrolyte composed of Al(OTf) 3 , In(OTf) 3 , and ethylene glycol (EG). In the bulk phase, EG strategically reconfigures the Al 3+ solvation sheath and reinforces the pervasive hydrogen‐bond network. This rigorously locks reactive free water to thermodynamically suppress the HER, while significantly lowering the desolvation energy barrier. Concurrently at the electrode–electrolyte interface, an aluminophilic metallic indium protective layer is dynamically formed in situ. This robust interfacial shield locally reduces the redox potential and serves as an active nucleation template, guiding uniform, dendrite‐free Al deposition. Benefiting from this precise spatiotemporal synergy, the Al||Al symmetric cell achieves stable cycling for 720 h at 0.1 mA cm −2 (0.1 mAh cm −2 ) and 220 h at 0.2 mA cm −2 (0.2 mAh cm −2 ). Moreover, the Al||Al x MnO 2 full cells maintain a high reversible capacity of 123 mAh g −1 after 600 cycles at 1 A g −1 . This work establishes a transformative paradigm for the rational design of intrinsically safe and long‐lasting aqueous metal‐ion batteries.