Loose Al 3+ Solvation Aggregates Enable Reversible Aluminum Anodes in Chlorine‐Free Electrolyte

ABSTRACT Sustained reversible Aluminum plating/stripping with long cycle life is scarcely realized in chlorine‐free organic electrolytes. The electrolyte formula exerts the deposition/stripping behavior of metal anodes. Highly polarizing Al 3+ cations show strong binding with electrolyte components, resulting in a significantly different ionic solvation structure from lithium. Here we reveal that pervasive compact ion aggregates (CAGs) solvation structures with an Al 3+ –Al 3+ interatomic distance of ∼5 Å were formed within typical ether or ester electrolytes, leading to low ionic conductivity and passivation interphases. On this basis, we developed a chlorine‐free ester electrolyte featuring loose solvation aggregates (LAGs) with an Al 3+ –Al 3+ interatomic distance of 7 Å through modulating the balance of Al 3+ coordination between the OTf − anion and solvent. Tris(pentafluorophenyl)borane (TPFPB) interacts with anions to suppress anion over‐coordination in Al 3+ solvation structures, thereby inducing an organic–inorganic hybrid solid electrolyte interphase (SEI). This loosely solvated Al 3+ electrolyte delivers nearly twofold enhanced ionic conductivity and a hybrid SEI, which endows the system with a low Al‐plating/stripping overpotential of ∼0.4 V and durable cycling exceeding 4000 h.