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

Abstract

A trifluoromethyl group (CF 3 -) 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 application 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 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 | LiCoO 2 coin cell.

Liquid electrolyte chemistries for solid electrolyte interphase construction on silicon and lithium-metal anodes

“…In particular, since the triuoromethyl group (CF 3 ) is a functional group with strong electron substituents, it can weaken the interaction between lithium-ions and uorinated solvent molecules. 240 In this manner, uorinated solvents reduce electrolyte viscosity by enhancing the mutual interaction between solvent-lithium-ion complexes while preserving the overall allowing the stable operation of LMBs at −10 °C. 262 Since the discovery of the important effects of uorinated solvents on changes in the solvation structure and the manipulation of SEI properties, the development of these solvents has drawn much attention (Fig.…”

Physical and Electrochemical Properties of Fluorinated Dialkyl Ethers

“…The kinematic viscosity may more clearly reflect the magnitude of the attractive forces between molecules. The kinematic viscosity of ETFEE was as low as that of DEE above 323 K. 1-(2,2,2-Trifluoroethoxy)-2-methoxyethane 7 and N,N-dimethyl trifluoroacetamide 10 also show low kinematic viscosities. The temperature dependency of kinematic viscosity of FETFEE was larger than that for the other solvents.…”

“…3,[5][6][7] We measured relative permittivities (¾ r ) or relative dielectric constants by the use of a LF impedance analyzer (Hewlett Packard, 4192A) that was connected to a thermostat (Ando Denki, TO-9). The electrostatic capacitances of air (C 0 ) and a sample (C sample ) were measured separately at a frequency of 1 MHz.…”

Emerging electrolytes with fluorinated solvents for rechargeable lithium-based batteries

“…Regarding interfacial compatibility, all these fluorinated ether electrolytes, especially trifluoro-ethers, exhibit higher cycling stability and CE than their non-fluorinated counterparts in Li metal-based cells. 84 Besides, trifluorinated ethers with shorter carbon-chain lengths delivered a higher CE at the same fluorine content. In the case of fluorinated ether sandwiched with fluorinated groups, the solvents with higher ion transportability exhibited better interfacial compatibility.…”

“…However, in the case of polyfluorinated and perfluorinated solvents, the individual dipole moments of the CÀF bonds are canceled, leading to extremely low polarity, and thus lower viscosity and capacity to dissolve lithium salts. 84 Therefore, polyfluorinated and perfluorinated solvents are capable of acting as unique media to regulate the viscosity, wettability, combustibility, and interfacial compatibility of electrolytes. [85][86][87] Solvation structure.…”