Use of monofluorinated ethyl propionates as solvents for lithium secondary batteries

Abstract

We have used 2-fluoroethyl propionate (2FEP), ethyl 2-fluoropropionate (E2FP), and ethyl 3-fluoropropionate (E3FP) as organic solvents for lithium secondary batteries. We describe the effect of position isomerism on the physical and electrochemical properties of monofluorinated ethyl propionates (EPs). The relative permittivities of E2FP and E3FP were higher than that of 2FEP, whereas the viscosity of E2FP was lower than those of 2FEP and E3FP. The ionic conductivities of 1 mol dm-3 LiPF6 solutions in E2FP and E3FP were higher than those in 2FEP and EP above room temperature. The use of 2FEP or E2FP as a co-solvent greatly improved discharge capacities of Li | LiCoO2 coin cells. © The Electrochemical Society of Japan.