Hydroxylated Ionic Liquids as Functional Additives for Stable Aqueous Zn Batteries

Rechargeable zinc (Zn) metal batteries are promising for large-scale energy storage due to their safety and affordability. However, Zn anodes in aqueous electrolytes suffer from uneven deposition and side reactions that impair battery performance and shorten lifespan. Herein, the use of a hydroxyl-functionalized ionic liquid, 1-hydroxyethyl-3-methylimidazolium triflate (HO-EMImTfO), as an electrolyte additive to stabilize the Zn anode is reported for the first time. This hydroxyl-functionalized ionic liquid acts through a dual mechanism: 1) the hydroxyl (─OH) group of HO-EMIm+ integrates into the Zn2+ solvation shell by displacing water molecules, altering the solvation structure, and suppressing water-induced side reactions; 2) HO-EMIm+ accumulates on the Zn surface, forming a HO-EMIm+-rich layer that facilitates lateral Zn2+ diffusion, promoting a uniform Zn deposition. The modulation of the Zn2+ solvation environment and interfacial ion flux effectively suppresses Zn pulverization and dendrite formation. Consequently, Zn||Cu cells with HO-EMImTfO achieve an average Coulombic efficiency of 99.5% over 1000 cycles at 4 mA cm−2, and Zn||V2O5 full cells retain 223.5 mAh g−1 after 1265 cycles at 1 A g−1. This work demonstrates the potential of strategically designed hydroxyl-functionalized ionic liquids for durable aqueous Zn batteries.