Structural Isomerism Effect on Physical and Electrochemical Properties of Monofluorinated Linear Carbonates

Abstract

Methyl propyl carbonate (MPC) shows a liquid temperature range that is wider than that of diethyl carbonate (DEC). Monofluorinated organic solvents exert the strong polar effect on the physical and the electrochemical properties. 2-Fluoropropyl methyl carbonate (2FPMC) and ethyl 2-fluoroethyl carbonate (E2FEC) are isomeric with each other. The relative permittivity and viscosity of 2FPMC were higher than those of E2FEC, MPC, and DEC. The ionic conductivity of 1 mol dm −3 LiPF 6 solution in 2FPMC was lower than those in E2FEC, MPC, and DEC. The use of 2FPMC as a co-solvent greatly improved cycling efficiency of a lithium anode.

Emerging electrolytes with fluorinated solvents for rechargeable lithium-based batteries

“…212 The bulk ion transport of F 2 DEC ( 3-2 )-based electrolytes was comparable with DEC at ambient temperature. 190,210 However, when the temperature was below 25 °C, the conductivities of F 2 DEC were lower than that of DEC. Meanwhile, the case was reversed when the temperature was elevated, indicating the high active energy of F 2 DEC-based electrolytes.…”

“…163 Thus, the fluorination of linear carbonates increases their dielectric constants. 210 For example, the dielectric constant of ethyl (2-fluoroethyl) carbonate (F 2 DEC, 3-2) was 6.5, which is larger than that of DEC (2.8). 190,211 Fig.…”

“…16c). 153,190,210 Similar to fluorinated cyclic carbonates, all fluorinated DEC derivatives inhibit the degree of ionic dissociation due to the lower electron-pair donicity of oxygen atoms and exhibit suppressed aluminum dissolution due to the formation of a passive layer composed of AlF 3 and AlO x F y . This passivation layer can be ascribed to the contact ion pair and ion aggregate in the solvation structures, which contributed to the anion-enriched cathode interphase with the formation of highly stable LiF (Fig.…”

“…16a). 210 Nevertheless, these associations are not monotonous, given that steric hindrance also affects the viscosity. In particular, the viscosity of TFDEC ( 3-4 ) is lower than that of the other fluorinated DEC derivates.…”

Physical and Electrolytic Properties of Monofluorinated Ethyl Acetates and Their Application to Lithium Secondary Batteries

“…However, the potentials for the oxidation decomposition of linear carboxylates (3.4 V vs. SCE for methyl acetate and methyl propionate [4]) are lower than those of linear carbonates (3.7 V vs. SCE for DMC, EMC, and DEC [4]). Partially fluorinated carbonates exert the polar effect on the physical and electrochemical properties such as relative permittivity, viscosity, electrolytic conductivity, and electrochemical stability [5]- [11]. Monofluorination of EA and ethyl propionate (EP) improved the anodic stability [12] [13].…”