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 LiAsF 6 and LiPF 6 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. LiC 6/PVDF-electrolyte/LiCoO 2 cells containing these multicomponent electrolyte solutions are stable and highly reproducible. Ambient temperature performance is essentially equal to comparative LiC 6/PVDF/LiCoO 2 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.