In this work, a 1:1 by weight blend of acetonitrile (AN) and gamma-butyrolactone (BL) was studied as the solvent of low temperature electrolyte for high energy density Li/CFx batteries. Both visual observation and impedance analysis show that metallic Li is kinetically stable in a 0.5 m 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/CFx cells. It is shown that the cell with such an electrolyte outperforms the control cell with 0.5 m 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/CFx cell. which is related to the high ionic conductivity of the AN/BL electrolyte. Due to the chemical incompatibility between metallic U and AN at high temperatures, the storage and operation temperature for the Li/CFx cells with 0.5 m LiBF4 1: 1 AN/BL electrolyte is limited to or below ambient temperature (30 degrees C). Published by Elsevier B.V.