The charge-discharge behavior of a lithium metal anode in propylene carbonate (PC) electrolyte containing added CO2 was investigated using in situ ac impedance measurements during galvanostatic cycling. In PC electrolyte with CO2, the anode’s cycle life was twice as long and its charge transfer resistance was smaller than in the same electrolyte without CO2. These enhancements are observed only when lithium is electrodeposited in the presence of CO2 on nickel substrate; the enhancement does not occur when lithium is deposited without CO2 and is cycled with CO2. Even large amounts of H2O in the electrolyte during cycling do not adversely affect the cycle life enhancement by CO2. The CO2 enhancement seems to be due to products formed by reaction of lithium with CO2 on the electrodeposited lithium surface.