Investigation of lithium-oxygen cells on discharge using a mixture of 16O16O and 18O18O gases, showed that O–O bond cleavage occurs during disproportionation of LiO2 to O2 and Li2O2, detected by the presence of isotopic 16O18O. The formation of singlet oxygen, 1O2, was also monitored during disproportionation. While only 4.5% of oxygen was found to undergo bond cleavage and scrambling of oxygen atoms, more than 40% of the singlet oxygen produced during disproportionation came from the scrambling pathway, making it a major source of singlet oxygen generation in lithium-oxygen batteries. Our results demonstrate that Li2O2 formation occurs predominantly by disproportionation, and by controlling the pathway of this step, it may be possible to suppress 1O2 formation, a species that has been implicated in the degradation of lithium-oxygen batteries.
