Singlet Oxygen in Lithium-Oxygen Batteries

Abstract

Singlet oxygen (O-1(2)) is one of the most critical species leading to parasitic side reactions and poor reversibility in non-aqueous Li-O-2 batteries. O-1(2) is generated via the disproportionation of the superoxide radical (O-2(.-)) in O-2/Li2O2 electrochemistry. The mechanistic and computational studies on O-1(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 O-1(2) production, trapping and eliminating O-1(2) have been attempted using molecular agents. Anthracene derivatives trap O-1(2) and form endoperoxides, which can be quantitatively detected using in situ fluorescence analysis. Physical quenchers that convert O-1(2) to O-3(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 O-1(2), and challenges and perspectives of suppressing the O-1(2) effect on the performance of Li-O-2 cells.