Trifluoroacetamide-Based Eutectic Electrolyte with High Oxidative Stability

Abstract

Recently, the development of batteries with high energy densities is strongly expected due to the downsizing of electronic devices and the popularization of electric vehicles. The highly concentrated eutectic electrolyte has been recognized as a promising candidate of electrolyte for the next generation batteries. Various compounds such as ether, sulfolane, acetonitrile, and others have been studied as solvents for eutectic electrolytes. Some kinds of amide-based eutectic electrolytes have been also reported so far, whereas their oxidation stability is insufficient for application as electrolytes for the high-voltage cathode materials in lithium-ion batteries. In the present study, to improve the oxidation stability of amide-based eutectic electrolytes, we have prepared trifluoroacetamide-based eutectic electrolytes with lithium bis(fluorolsulfonyl)amide (LiFSA) and investigated their solution structure, physicochemical properties, and the potential for the electrolytes. Eutectic electrolyte composed of LiFSA and N-methyltrifluoroacetamide (MTFAA) at a molar ratio of 1:1.5 exhibited the reversible deposition and dissolution of lithium and very high electrochemical oxidation stability. We have also demonstrated the stable charge/discharge cycling of a high-voltage Li metal battery with a 5 V-class LiNi0.5Mn1.5O4 cathode using the electrolyte.