Interfacial chemistry modulation of Zn anodes via an EMImI ionic liquid additive for stable aqueous zinc-ion batteries

Abstract

Uncontrolled side reactions and dendrite growth on Zn anodes present significant challenges to the commercial application of aqueous zinc-ion batteries (AZIBs). Using an electrolyte additive is recognized as an effective approach with operational convenience and multifunctionality for achieving stable AZIBs. Herein, a 1-ethyl-3-methylimidazolium iodide (EMImI) ionic liquid was introduced into the electrolyte to stabilize the Zn anode. The characterization studies revealed that EMIm⁺ and I⁻ could be selectively adsorbed on the Zn surface to generate a water-deficient electric double layer and promote the formation of a ZnS/ZnI₂-rich gradient solid electrolyte interface (SEI). The water decomposition-induced side reactions were subsequently suppressed with enhanced zinc deposition kinetics. Notably, the selective adsorption of cations and anions on different crystal planes induced preferentially (002) oriented dendrite-free zinc deposition behavior and ultimately achieved high performance in AZIBs. Experimental results confirmed that the EMImI-modulated interfacial chemistry significantly improved the stability and reversibility of the Zn anode, resulting in Zn//Zn symmetric cells with an ultra-long lifespan exceeding 7100 hours at 1 mA cm⁻² and 1 mAh cm⁻². The Zn//PANI full cells containing EMImI also exhibited outstanding cycling stability, i.e., 68.7% capacity retention after 2700 cycles at 0.5 A g⁻¹ and over 10 000 stable cycles at 5 A g⁻¹ and 10 A g⁻¹. This work provides an ion-based electrolyte-engineering strategy for achieving highly stable and reversible Zn anodes.