Low temperature electrolytes for Li-ion PVDF cells

New electrolyte solutions based on ternary and quaternary solvent mixtures containing significant amounts of toluene (tol) have been evaluated. Liquid electrolytes containing LiAsF6 and LiPF6 exhibit electrolytic conductivities >1 S cm−1 down to −50°C. When incorporated into PVDF host matrixes, these multicomponent solutions exhibit reduced conductivities but still remain sufficiently high, yielding useful conductivities down to at least −40°C. LiC6/PVDF-electrolyte/LiCoO2 cells containing these multicomponent electrolyte solutions are stable and highly reproducible. Ambient temperature performance is essentially equal to comparative LiC6/PVDF/LiCoO2 cells containing ternary mixtures such as ethylene carbonate (EC):dimethyl carbonate (DMC):diethyl carbonate (DEC) and EC:ethylmethyl carbonate (EMC):DMC; but at −20°C, −30°C and −40°C, cells containing the quaternary mixed solvent EC:EMC:methyl acetate (MA):tol are clearly superior. Capacity retention of cells utilizing this quaternary solvent in PVDF at −40°C is 50% of nominal capacity at ambient temperatures.