Breaking the Additive Paradox in Aqueous Aluminum-Ion Batteries via Weak-Coordination Asymmetric Electrolyte Chemistry.

Aqueous aluminum-ion batteries (AAIBs) are compelling for sustainable storage, yet the strong hydrolysis of Al3+ acidifies the electrolyte, causing corrosion and passivation that necessitate modification. Additives designed to break the rigid Al3+ solvation shell face a paradox: they often compromise reversibility via either dielectric collapse or kinetic deadlocks. Here, we break this paradox by establishing a weak-coordination asymmetric electrolyte based on aluminum trifluoromethanesulfonate (Al(OTF)3), dimethyl sulfoxide (DMSO), and fluoroethylene carbonate (FEC). DMSO coordinates to Al3+, displacing coordinated water to suppress water activity, but cannot preserve the dielectric environment. FEC compensates via three synergistic functions: high dielectric constant for electrostatic screening, weak hydrogen bonding for solvation asymmetry reinforcement, and reductive decomposition for solid electrolyte interphase(SEI) formation. The sequential coupling of DMSO-mediated solvation disruption with FEC-enables dielectric/interfacial compensation accelerates desolvation and stabilizes electrode: a fluorinated SEI enables 2000 h reversible Al plating/stripping, while a spinel-to-layer transformation creates a fluorinated interface on vanadium oxide with asymmetric channels, mitigating dissolution. The full cell retains 90.8% capacity after 2000 cycles at 4 A g-1. By showing that resolving one bottleneck can expose another, this work reframes additive optimization as sequential processes of identifying and compensating coupled failure mechanisms, generalizing a design principle for multivalent aqueous electrolytes.