Singlet oxygen and dioxygen bond cleavage in the aprotic lithium-oxygen battery

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.