The effects of Li utilization on the capacity and cycle stability of Li-O2 batteries were studied by investigating the performance of cells incorporating varying ratio of Li metal to air electrode catalyst. The quantity of Li metal was found to affect the overall discharge capacity, such that the capacity decreased with decreasing amounts of Li in the anode. Although a capacity of only 354 mAhg-1 (cathode) was obtained when the anode contained 0.9mg Li, almost 100% of the Li in the cell was consumed during discharge, which corresponds to a capacity of 3932 mAhg-1 (Li). The cycle stability of cells operating under high Li utilization conditions was, however, significantly reduced. Detailed analysis of the Li distribution in the cell suggests that decreased usage of Li within the first few cycles is the cause of the poor cycle stability. The results of this study suggest that low cycle stability in a Li-O2 battery may be attributed to the formation of a surface passivation layer on the Li metal composed primarily of Li 2CO3 and ROCO2Li and generated by reaction with the electrolyte. ? 2014 The Electrochemical Society of Japan.