pH-Regulated Acetate-Based Aqueous Electrolyte and Its Impact on Zinc Utilization for Zinc Metal Batteries

Water-in-salt electrolytes (WiSE) have been successfully used to expand the operating potential of aqueous electrolytes for zinc metal batteries, increasing their energy density. Acetate-based concentrated electrolytes are low cost and safe, yet their technological development has been hindered by insufficient understanding and control of zinc electrochemistry, morphology, and reversibility, particularly at realistic current densities and high zinc utilization. In this work, zinc stability and discharge behavior were studied in concentrated and dilute potassium acetate (KOAc)-based electrolytes using electrochemical, computational, and spectroscopic tools. The impact of high salt concentrations on the working electrochemical windows of the electrolytes were measured, where the largest electrochemical window of 3.15 V (vs. Zn/Zn2+) was observed for 27 m KOAc. However, dilute acetate electrolytes provided greater zinc utilization with minimal reduction of electrolyte stability. Zinc foil was discharged in acetate-based electrolytes with different compositions, revealing that mild acidification of 5 m KOAc prevents inactive zinc oxide formation and enables up to 80% zinc utilization at current densities of 5 mA/cm2. This study lays the groundwork for understanding and developing acetate-based electrolytes in the pursuit of high energy density, aqueous zinc batteries.