Constructing Nonaqueous Rechargeable Zinc-Ion Batteries with Zinc Trifluoroacetate

Rechargeable zinc-ion batteries (RZIBs) are recognized as promising alternative energy storage techniques for large-scale application. Using organic electrolytes with wide electrochemical stability windows to construct nonaqueous RZIBs enables high operating voltage and energy density. However, the selection of zinc salts with cost-effectiveness and excellent electrochemical performance for nonaqueous electrolytes is limited. In this work, the electrochemical properties of a competitive zinc salt, zinc trifluoroacetate (Zn­(TFA)2), are investigated in acetonitrile and triethyl phosphate. It is found that the Zn­(TFA)2 is highly soluble in the organic solvents, reaching 15 mol·kg–1 in acetonitrile. The Zn­(TFA)2 electrolytes show a wide electrochemical stability window of 2.2 V, good conductivity of 6.14 mS·cm–1 at 1.0 mol·kg–1, and good compatibility with the Zn metal anode. Zn­(TFA)2 tends to form ion pairs or aggregates in triethyl phosphate, which improve the electrochemical stability but partially expense the ionic conductivity. Full batteries are fabricated with the Zn­(TFA)2 electrolytes using potassium manganese hexacyanoferrate as the cathode. The batteries with Zn­(TFA)2-AN-TEP (19%) electrolyte deliver a high specific density of 181.9 Wh·kg–1 at 0.1 A·g–1 and excellent cyclic stability with a capacity retention rate of 71.7% after 1000 cycles at 0.5 A·g–1. Our results suggest that the Zn­(TFA)2 is a promising candidate of zinc salts in the application of nonaqueous RZIBs.