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

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>i.e.</i>, 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.