Constructing Nonaqueous Rechargeable Zinc-Ion Batteries with Zinc Trifluoroacetate

Abstract

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.