Singlet Oxygen in Lithium−Oxygen Batteries

Singlet oxygen ( 1 O 2 ) is one of the most critical species leading to parasitic side reactions and poor reversibility in non‐aqueous Li−O 2 batteries. 1 O 2 is generated via the disproportionation of the superoxide radical (O 2 .− ) in O 2 /Li 2 O 2 electrochemistry. The mechanistic and computational studies on 1 O 2 formation revealed the significant roles of the associated cations, solvation ability of aprotic solvents, H + source, and catalyst/electrode materials. Along with efforts to alleviate 1 O 2 production, trapping and eliminating 1 O 2 have been attempted using molecular agents. Anthracene derivatives trap 1 O 2 and form endoperoxides, which can be quantitatively detected using in situ fluorescence analysis. Physical quenchers that convert 1 O 2 to 3 O 2 are desirable for cycling of Li−O 2 cells because quencher molecules are reusable. We highlight the recent reports on the formation and elimination of 1 O 2 , and challenges and perspectives of suppressing the 1 O 2 effect on the performance of Li−O 2 cells.