Dual-anion-coordinated solvation sheath for stable aqueous zinc batteries

Zinc (Zn) metal is a promising anode for aqueous batteries but is hindered by poor reversibility caused by dendrite growth and water-induced parasitic reactions (e.g., hydrogen evolution reaction and Zn corrosion). Here, a dual-anion-coordinated Zn2+-solvation sheath involving the trifluoromethanesulfonate (OTf−) anion and ethylenediaminetetraacetate (Y4−) anion is proposed to stabilize Zn anodes. Theoretical and experimental studies reveal that such a solvation structure not only weakens the water activity by decreasing the solvating-H2O content but also guides the homogeneous Zn2+ plating process. Moreover, this solvation structure enables the in-situ formation of an organic-inorganic solid-electrolyte interphase (SEI) on Zn derived by the decomposition of coordinated anions. This Zn2+-conducting SEI can isolate the active Zn from the bulk electrolyte and thus suppress water-induced side reactions. The tailored electrolyte composed of 1 M Zn(OTf)2 + 100 mM Na4Y enables high reversibility of Zn//Cu cell (99.7% Coulombic efficiency over 400 cycles at 1.0 mA cm−2) and long-term stability of Zn//Zn cell (over 1600 h at 1.0 mA cm−2 and 1.0 mAh cm−2), whilst it can well support the stable operation of Zn//VO2 full battery. This work provides an efficient electrolyte engineering strategy to improve the Zn reversibility and realize long-life aqueous batteries.