Solvation-Structure Design of Multicomponent Eutectic Electrolytes Enabling Al-Rich Alloy Growth in Aqueous Aluminum-Ion Batteries

Abstract

Aqueous aluminum-ion batteries (AAIBs) offer intrinsic safety, low cost, and high volumetric capacity, but strong hydration of Al 3+ imposes large desolvation barriers and promotes parasitic reactions, resulting in sluggish deposition and poor durability. Here, we report a deep eutectic electrolyte (DEE) comprising Al(ClO 4 ) 3 ·9H 2 O, acetamide, propylene glycol, and water in a molar ratio of 1:40:20:20. This multicomponent formulation creates a dynamically balanced organic–water environment tailored to the strong polarization of Al 3+ . The resulting electrolyte forms a diverse and uniformly distributed hydrogen-bond network, giving rise to an adaptive solvation structure. This network supports a dual-layer architecture─with a coordination-dominated inner core and a hydrogen-bond-governed shell─that enhances Al 3+ electrochemistry. It suppresses free-water activity, mitigates hydrogen evolution reaction, and broadens the electrochemical stability window to 3.64 V. These effects lower interfacial resistance and facilitate Al 3+ transfer kinetics. Consequently, relative to Al(ClO 4 ) 3 (aq) and other substrates (Al/Sn/Ni), the Al 3+ -DEE promotes Al-enriched codeposition on Zn, forming Al-rich Al–Zn alloys. Coupled with a poly(1,5-diaminoanthraquinone) (PDAAQ) cathode, the Zn/Al 3+ -DEE/PDAAQ full cell delivers 135 mAh g –1 at 1 A g –1 with 94% retention during 1700 cycles, along with a higher voltage plateau and reduced polarization. Our findings underscore the importance of solvation-structure design tailored to multivalent-ion characteristics for achieving high-performance AAIBs.