Physical and Electrolytic Properties of Trifluorinated Linear Ethers and Their Application to Lithium Secondary Batteries

Abstract

A trifluoromethyl group (CF3-) is a strong electron-withdrawing substituent. The trifluoromethyl is much larger than a methyl group. We have investigated the physical and electrolytic properties of trifluorinated linear ethers as solvents and their applications to lithium secondary batteries. We synthesized 1-(2,2,2-trifluoroethoxy)-2-methoxyethane (TFEME) as a trifluorinated diether and 1-(2,2,2-trifluoroethoxy)-2-(2-methoxyethoxy)ethane (TFEMEE) as a trifluorinated triether. Three fluorine atoms of TFEME and TFEMEE are situated on the same terminal carbon atom of the ethyl group. The mass densities, relative permittivities, viscosities, and anodic stabilities of TFEME and TFEMEE were higher than those of the corresponding nonfluorinated linear ethers (1-ethoxy-2-methoxyethane (EME) and 1-ethoxy-2-(2-methoxyethoxy)ethane (EMEE)). The presence of the trifluomethyl group can weaken the attractive forces between molecules. The kinematic viscosities of TFEME and TFEMEE were as low as those of the corresponding nonfluorinated linear ethers especially at high temperatures. The use of an EC−TFEME or an EC−TFEMEE binary mixture improved the cycling efficiency of a lithium anode and the discharge capacity of a Li | LiCoO2 coin cell.