Mixed solvent electrolyte for high voltage lithium metal secondary cells

We have examined various solvents and solutes as electrolytes for high voltage lithium metal secondary cells in terms of the oxidation potential, specific conductivity and cycling performance of Li/LiMn1.9Co0.1O4 cells. We selected propylene carbonate (PC), ethylene carbonate (EC), dimethyl carbonate (DMC), diethyl carbonate (DEC), 1,2-dimethoxyethane (DME) and 1,2-diethoxyethane (DEE) as the solvents, and LiClO4, LiPF6, LiAsF4 and LiBF4 as the solutes. Of the mixed solvent electrolytes we used, 1.0 mol dm−3 LiPF6 in a mixture of EC and DMC with a ratio of 1:1, provided a high figure of merit (FOM) of 43.5 for lithium cycling efficiency with Li/LiMn1.9Co0.1O4 cells as well as a high potential of over 5 V vs. Li/Li+ and a high specific conductivity of 3.1 mS cm−1 at −20°C and 18.7 mS cm−1 at 60°C.