Application to Lithium Batteries of Ternary Solvent Electrolytes with Ethylene Carbonate – 1,2-Dimethoxyethane Mixture

Abstract

ABSTRACTThe electrolytic conductivity, the lithium cycling efficiency of lithium electrode and the energy density for Li/V2O5(2025) coin-type cell were examined in ternary solvent electrolytes containing LiPF6and LiClO4with ethylene carbonate(EC) – 1,2-dimethoxyethane(DME) equimolar binary mixture at 25°C. The solvents applied to EC – DME mixture are dimethyl carbonate(DMC), ethyl methyl carbonate(EMC), diethyl carbonate(DEC), 1,3-dioxolane(DOL), 2,2-bis(trifluoromethyl)-1,3-dioxolane(TFMDOL), 1,3-dimethy1–2-imidazolidinone(DMI) and 1-methyl-2-pyrrolidinone(NMP). The order of decrease of the molar conductivities in ternary solvents electrolytes except DMI and NMP systems is agreement with that of increase in viscosities of the solvents applied to EC – DME binary mixture. The molar conductivities in ternary solvent electrolytes containing DMI and NMP are mainly affected by the dielectric constants rather than viscosities of mixed solvents. The energy density of Li/V2O5(2025) coin-type cell in LiPF6/EC – DME – DOL electrolyte with the highest molar conductivity was 500 Wh kg−1, which is the highest value in every ternary electrolyte. The lithium cycling efficiency(charge - discharge coulombic cycling efficiency of lithium electrode) in EC – DME – EMC, EC – DME – DMI and EC – DME – TFMDOL electrolytes containing LiPF6is more than 75% at 40 cycle numbers. The lithium electrodeposition on the Ni(working) electrode surface in ternary solvent electrolytes by cyclic voltammetry was observed by atomic force microscopy(AFM) and scanning electron microscope(SEM).