Dual‐Anion Zn ²⁺ Electrolytes having Sulfate and Triflate for Highly Reversible and Stable Operation of Zinc Metal Anode

Zinc‐ion batteries (ZIBs) have emerged as a viable option for energy storage applications in response to the growing need for energy due to their low cost, acceptable energy density, high natural abundance, high safety, and high volumetric and gravimetric capacity due to the divalent nature of Zn 2+ . However, it is necessary to extend the longevity of ZIBs by optimizing Zinc‐ion electrolytes for the stable operation of the Zn metal anode, where passivation layers suppress its corrosion and dendritic growth. Herein, an electrochemical quartz‐crystal microbalance analysis is conducted to characterize passivation layers formed during the deposition/dissolution of zinc metal in aqueous electrolyte solutions of zinc sulfate (ZnSO 4 ), zinc triflate (Zn(OTf) 2 ), and their mixture at varied ratios as dual‐salt hybrid electrolytes. The varied anionic compositions result in different passivation behaviors with characteristic reversibility and potential‐dependency. Specifically, mixed electrolytes exhibit more stable and efficient operation of the zinc metal anode by the formation of passivation layers with balanced robustness and reversibility. The mass‐per‐electron value is close to the ideal value for the optimized electrolyte solution, evidencing the importance of electrolyte formulation for advanced ZIB technologies toward safer and more energy‐dense aqueous energy storage devices.