Operando Fluorescence Detection of Singlet Oxygen inside High-Performance Li-O2 Batteries

It has been established that the Li-O2 battery with the highest energy density, comparable to fossil fuels, undergoes parasitic reactions with degradation of electrolyte and cathode material, which limits the number of cycles due to the formation of very reactive singlet oxygen because of superoxide disproportionation. We present herein for the first time the detection of singlet oxygen inside the battery during the discharge of an aprotic Li-O2 battery in operando by means of a bifurcated optical fiber. The identification of singlet oxygen, 1O2, is based on its reactivity toward the fluorescent probe 9,10-dimethylanthracene (DMA) which is added to the electrolyte rapidly and selectively traps 1O2 by forming its non-fluorescent endoperoxide (DMA-O2) and can be detected in operando following DMA fluorescence decay. Furthermore and as a proof of concept, addition of azide ions, a wellknown specific physical quencher of singlet oxygen, improved Li-O2 battery discharge-charge cycling performance at 125-250 mA/g current densities. The new in-operando method is well suited to test new strategies in high-performance Li-O2 batteries.

Automated summary

It has been discovered that the Li-O2 battery, which has the highest energy density comparable to fossil fuels, experiences parasitic reactions leading to degradation of the electrolyte and cathode material. These reactions limit the number of cycles due to the superoxide disproportionation that forms highly reactive singlet oxygen. This study introduces a novel in-operando method using a bifurcated optical fiber to detect singlet oxygen inside the battery during discharge. The detection is based on the reactivity of singlet oxygen with a fluorescent probe, which allows for real-time monitoring of singlet oxygen concentration. Additionally, the addition of azide ions, a well-known quencher of singlet oxygen, improves the cycling performance of Li-O2 batteries.