Ionic liquid additive enabling anti-freezing aqueous electrolyte and dendrite-free Zn metal electrode with organic/inorganic hybrid solid electrolyte interphase layer

Abstract

• [BMIM]OTF ionic liquid is used as the electrolyte additive for zinc-ion batteries. • The modified electrolyte can offer very large ionic conductivity at –40°C. • The [BMIM]OTF enables the formation of an organic/inorganic hybrid SEI layer. • The Zn deposition process is homogenized and parasitic side reactions are inhibited. • The full battery with [BMIM]OTF exhibits excellent performances even at −30°C. Benefiting from intrinsic safety, low cost, and competitive energy density, aqueous zinc-ion batteries (AZIBs) have attracted tremendous research interest, whereas suffering from low stability of Zn metal anode in aqueous electrolytes. Herein, 1-butyl-3-methylimidazolium trifluoromethanesulfonate ([BMIM]OTF), a water-soluble ionic liquid with very low melting point, is used as the electrolyte additive. The addition of [BMIM]OTF only slightly influences the ionic conductivity of 3 M Zn(OTF) 2 aqueous electrolyte at room temperature, while considerably improving the tolerance to low temperatures. This additive is also found to be preferentially adsorbed on the Zn electrode, tune the solvation sheath of hydrated Zn 2+ ions, reduce the corrosion activity of Zn electrode, and enable the formation of an organic/inorganic hybrid solid electrolyte interphase (SEI) layer. Such SEI layer is zincophilic and hydrophobic, thereby decreasing the nucleation overpotential of Zn plating, enhancing the interfacial charge transfer kinetics, homogenizing the Zn deposition behavior, and inhibiting parasitic side reactions. With the [BMIM]OTF-modified electrolyte, the Zn//Zn symmetric cell offers good cyclability even under extremely large areal capacity of 25 mAh cm −2 . And the assembled AZIB with an Al-vanadate cathode material exhibits excellent performances even at −30°C. This work provides new insights into stabilizing aqueous batteries.