Synergistic Anion–Cation Chemistry Enables Highly Stable Zn Metal Anodes

Engineering aqueous electrolytes with an ionic liquid (IL) for the zinc (Zn) metal anode has been reported to enhance the electrochemical performances of the Zn metal batteries (ZMBs). Despite these advancements, the effects of IL and the mechanisms involving their anions and cations have been scarcely investigated. Here, we introduce a novel electrolyte design strategy that synergizes anion–cation chemistry using a halogen-based IL and elucidates the underlying mechanism. The strongly and preferentially adsorbed halogen anions guide the formation of a water-poor electrical double layer (EDL) by imidazole-based cations, resulting in the formation of a halide-rich inorganic interphase. This synergistic interaction significantly mitigates Zn anode corrosion at the anode–electrolyte interface, while the halide-rich interphase promotes dense Zn deposition. Consequently, the battery exhibits superior performance, including high reversibility (99.74%) and an ultralong cycle life (20,000 cycles). This synergistic anion–cation chemistry strategy combines the traditional single solid electrolyte interphase and the classic EDL mechanism, substantially enhancing the electrochemical performance of ZMBs.