Physical and Electrolytic Properties of Fluoroethyl Methyl Carbonate

Abstract

The physical and electrolytic properties of the fluoroethyl methyl carbonate (FEMC) obtained chemically were examined. The dielectric constant, density and viscosity of FEMC were much higher than those of ethyl methyl carbonate (EMC). This means that the molecular interaction in FEMC becomes large with introducing a fluorine atom with high electron withdrawing into EMC molecule. The oxidative decomposition voltage (oxidation durability) of FEMC is slightly higher than that of EMC. At relatively low electrolyte concentrations, the specific conductivities in FEMC solutions are higher than those in EMC solutions because of high dielectric constant for FEMC. The conductivity in EC-FEMC binary solution decreases gradually with increasing FEMC concentration. The lithium electrode cycling efficiencies in EC-FEMC equimolar binary solutions containing 1.0 mol dm⁻³ LiPF₆ and LiBF₄ are higher than those in EC-EMC solutions. In particular, the LiBF₄ solution shows the high efficiency of more than 70% at a high range of cycle number. The surface of the films formed on the electrode after cycling in EC-FEMC solutions is homogeneous, and consists of an uniform and small grain size.