Singlet Oxygen Generation as a Major Cause for Parasitic Reactions during Cycling of Aprotic Lithium-Oxygen Batteries

TL;DR

This paper demonstrates that singlet oxygen is a major cause of parasitic reactions in lithium-oxygen batteries, affecting their efficiency and cycle life, and suggests strategies to mitigate these effects.

Contribution

It reveals the formation of singlet oxygen during battery cycling and its role in parasitic reactions, providing new insights into improving battery reversibility.

Findings

Singlet oxygen forms at the cathode during discharge and charge.

Presence of trace water enhances singlet oxygen formation.

Quenchers can reduce parasitic reactions effectively.

Abstract

Non-aqueous metal-oxygen batteries depend critically on the reversible formation/decomposition of metal oxides on cycling. Irreversible parasitic reactions cause poor rechargeability, efficiency, and cycle life and have predominantly been ascribed to the reactivity of reduced oxygen species with cell components. These species, however, cannot fully explain the side reactions. Here we show that singlet oxygen forms at the cathode of a lithium-oxygen cell during discharge and from the onset of charge, and accounts for the majority of parasitic reaction products. The amount increases during discharge, early stages of charge, and charging at higher voltages, and is enhanced by the presence of trace water. Superoxide and peroxide appear to be involved in singlet oxygen generation. Singlet oxygen traps and quenchers can reduce parasitic reactions effectively. Awareness of the highly reactive singlet oxygen in non-aqueous metal-oxygen batteries gives a rationale for future research towards achieving highly reversible cell operation.