Singlet Oxygen in Lithium−Oxygen Batteries

Abstract

Singlet oxygen (1O2) is one of the most critical species leading to parasitic side reactions and poor reversibility in non‐aqueous Li−O2 batteries. 1O2 is generated via the disproportionation of the superoxide radical (O2.−) in O2/Li2O2 electrochemistry. The mechanistic and computational studies on 1O2 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 1O2 production, trapping and eliminating 1O2 have been attempted using molecular agents. Anthracene derivatives trap 1O2 and form endoperoxides, which can be quantitatively detected using in situ fluorescence analysis. Physical quenchers that convert 1O2 to 3O2 are desirable for cycling of Li−O2 cells because quencher molecules are reusable. We highlight the recent reports on the formation and elimination of 1O2, and challenges and perspectives of suppressing the 1O2 effect on the performance of Li−O2 cells.

Study of the Electronic Structure of Alkali Peroxides and Their Role in the Chemistry of Metal–Oxygen Batteries

“…In particular, LiO 2 is a radical intermediate both in the electrochemical reduction of O 2 and in the oxidation of Li 2 O 2 . , Despite its simplicity, reactions such as hide a very complex mechanism that involves singlet–triplet spin intersystem crossing while evolving from two doublet LiO 2 radicals. − Due to the coexistence of electronic states of different multiplicities, the disproportionation product can be either 1 O 2 (singlet oxygen) or 3 O 2 (triplet, ground-state oxygen). , The formation of singlet oxygen, which is a highly reactive biradical molecule, is at the origin of parasitic degradation reactions during electrochemical charge/discharge cycles. As expected, 1 O 2 release leads to battery death upon cycling. − …”

Revealing the Local Cathodic Interfacial Chemism Inconsistency in a Practical Large-Sized Li–O2 Model Battery with High Energy Density to Underpin Its Key Cyclic Constraints

“…As with the C 1s spectra of the deeply charged cathodes (Figure b,f), a generally intensified oxidation can be observed in all four regions, including the increase of the above-mentioned C–O bond from the degraded TEGDME solvent as well as the CO bond from further oxidation of the C–O bond. The disappearance of the HCOO– peak in Region D suggested that it can be decomposed, while its appearance in Regions A and B after charge may be related to the local side reactions of the solvent with the singlet oxygen formed by the Li 2 O 2 oxidation during charge − due to their almost 3 times yield as that of Region D. Besides, the number of “C-C” from the SP carbon substrate also decreased in these regions, further implying the worsening and corrosion of the initial carbon surface after charge. Moreover, all of the −CF 2 signals of the binder in the four regions disappeared, which should have been covered by the thick byproduct layer as shown in the SEM images in Figure a′–d′, as the XPS technique only gives the surface information within about 2–10 nm in depth.…”

Low-Temperature CO2-Assisted Lithium–Oxygen Batteries for Improved Stability of Peroxodicarbonate and Excellent Cyclability

“…These results reveal the necessity of limiting the Li 2 CO 3 quantity in Li-O 2 /CO 2 cells. In addition, the elongated capacity over 4 V suggested the decomposition of carbonaceous electrodes and electrolyte solution and the possible formation of singlet oxygen, causing capacity fading. ,, …”