In this work, a 1:1 by weight blend of acetonitrile (AN) and γ-butyrolactone (BL) was studied as the solvent of low temperature electrolyte for high energy density Li/CF x batteries. Both visual observation and impedance analysis show that metallic Li is kinetically stable in a 0.5m LiBF4 1:1 AN/BL electrolyte. This property is attributed to the formation of a protective passivation film on the surface of metallic Li, and it has been successfully used to develop the low temperature electrolyte for Li/CF x cells. It is shown that the cell with such an electrolyte outperforms the control cell with 0.5m LiBF4 1:1 (wt.) propylene carbonate (PC)/1,2-dimethoxyethane (DME) electrolyte in both power capability and low temperature discharge performance. Impedance analyses reveal that the improved discharge performance is attributed to the reduction in both the bulk resistance and cell reaction resistance of the Li/CF x cell, which is related to the high ionic conductivity of the AN/BL electrolyte. Due to the chemical incompatibility between metallic Li and AN at high temperatures, the storage and operation temperature for the Li/CF x cells with 0.5m LiBF4 1:1 AN/BL electrolyte is limited to or below ambient temperature (30°C).