Implications of CO2 Contamination in Rechargeable Nonaqueous Li-O2 Batteries

In this Letter, the effect of CO2 contamination on nonaqueous Li-O-2 battery rechargeability is explored. Although CO2 contamination was found to increase the cell's discharge capacity, it also spontaneously reacts with Li2O2 (the primary discharge product of a nonaqueous Li-O-2 battery) to form Li2CO3. CO2 evolution from Li2CO3 during battery charging was found to occur only at very high potentials (>4 V) compared to O-2 evolution from Li2O2 (similar to 3-3.5 V), and as a result, the presence of CO2 during discharge dramatically reduced the voltaic efficiency of the discharge-charge cycle. These results emphasize the importance of not only completely removing CO2 from air fed to a Li-air battery, but also developing stable cathodes and electrolytes that will not decompose during battery operation to form carbonate deposits.