Anion-induced optimization of non-aqueous zinc-air battery performance: Insights into OTF− selection

Abstract

Rechargeable non-alkaline zinc-air batteries (ZABs) address the CO₂ incompatibility and instability issues of conventional alkaline batteries. However, the impact of solid discharge products like zinc oxide on discharge capacity at the air cathode remains unexplored. In this study, we investigate how anions influence ion pair solvation structures using Zinc trifluoromethanesulfonate (Zn(OTF)₂)-N, N-dimethylformamide (DMF) and Zinc acetate (Zn(Ac)₂)-DMF electrolytes, and how these structures affect the distribution of discharge product. Our finding shows that anions with lower donor numbers (DNs), like the weaker ligand OTF^- (20.5), enhance the zinc ion activity and promote rapid Zn²⁺ reactions with oxygen during discharge, leading to a more than tenfold increase in discharge capacity. In contrast, acetate anions with higher DNs (43.3) form stable complexes, inhibiting zinc ion activity and causing the formation of film-like discharge products, which reduces ZAB performance. The Zn(OTF)₂-DMF electrolyte also enables a battery lifespan of over 200 h, more than fivefold compared to the acetate-based system.