An Acetate-Modulated Mixed-Solvation Hybrid Electrolyte Enabling a Stable Zn Anode and an Al Current Collector for Durable Zn-Ion Supercapacitors

A durable and cost-effective Zn-ion supercapacitor (ZIS) is realized by engineering a hybrid electrolyte (1-HYB) based on 1 mol kg^-1 zinc acetate dihydrate (Zn(OAc)₂·2H₂O) salt dissolved in a mixture of acetonitrile (AN) and the ionic liquid 1-ethyl-3-methylimidazolium acetate (EMImOAc). In this system, Zn(OAc)₂·2H₂O serves as an inexpensive, readily available salt that introduces only trace amounts of water into the electrolyte. Molecular dynamics simulations reveal that Zn²⁺ is predominantly coordinated by acetate anions in bidentate and monodentate forms, creating a mixed-solvation environment with minor contributions from H₂O and AN molecules. This tailored solvation structure mitigates detrimental Zn²⁺-H₂O interactions and suppresses parasitic side reactions at the Zn metal anode. Importantly, 1-HYB ensures stable operation with low-cost, lightweight, and scalable Al current collectors, which are susceptible to corrosion in aqueous electrolytes. The practical viability of 1-HYB is demonstrated in a ZIS device comprising a Zn metal anode, an activated carbon cathode, and an Al current collector, which delivers competitive charge storage kinetics, enhanced cycling stability, and superior low-temperature performance. Overall, this work presents a pragmatic and scalable strategy for designing nonaqueous Zn-ion electrolytes by controlling, rather than eliminating, trace water content through diluted hydrated salt solutions in organic media. This approach enables the use of low salt concentrations, providing a cost-effective and compositionally simple alternative to water-in-salt electrolytes, which rely on high loadings of expensive salts in water.