Singlet Oxygen during Cycling of the Aprotic Sodium–O₂ Battery

Abstract

Aprotic sodium–O2 batteries require the reversible formation/dissolution of sodium superoxide (NaO2) on cycling. Poor cycle life has been associated with parasitic chemistry caused by the reactivity of electrolyte and electrode with NaO2, a strong nucleophile and base. Its reactivity can, however, not consistently explain the side reactions and irreversibility. Herein we show that singlet oxygen (1O2) forms at all stages of cycling and that it is a main driver for parasitic chemistry. It was detected in‐ and ex‐situ via a 1O2 trap that selectively and rapidly forms a stable adduct with 1O2. The 1O2 formation mechanism involves proton‐mediated superoxide disproportionation on discharge, rest, and charge below ca. 3.3 V, and direct electrochemical 1O2 evolution above ca. 3.3 V. Trace water, which is needed for high capacities also drives parasitic chemistry. Controlling the highly reactive singlet oxygen is thus crucial for achieving highly reversible cell operation.

Pathways to Triplet or Singlet Oxygen during the Dissociation of Alkali Metal Superoxides: Insights by Multireference Calculations of Molecular Model Systems

“…The gained resultsi ndicate similar mechanisms of singlet-oxygen formation for LiO 2 and NaO 2 .Furthermore, formation may be also possible for KO 2 systems by applying higher potentials and, at least for NaO 2 , there is already experimental evidence. [14] The gained knowledge on the underlying dissociation mechanism of the alkali metal superoxides can give access to strategies to avoid the formation of the highly reactives inglet oxygen. First, it could be investigated whether ab eneficial choice of solvent/surface structure combination shifts the electronic dissociation curve with the path to the lithium cation and the superoxide anion between the formation curves for tripleta nd singlet oxygen, so that either triplet-oxygen formation or dissociation to the ionic components takes place (see Figure 7).…”

DABCOnium: An Efficient and High‐Voltage Stable Singlet Oxygen Quencher for Metal–O2 Cells

“…[1a,b,f,2b-e,3] (Su)peroxidesreactivities as strong nucleophiles and bases could, however,not fully explain the parasitic reactions. [4] Superoxide disproportionation to Li 2 O 2 was suggested as the source of 1 O 2 , which has been shown to react with electrolyte and carbon. [4] Superoxide disproportionation to Li 2 O 2 was suggested as the source of 1 O 2 , which has been shown to react with electrolyte and carbon.…”

“…[1f, 2b,3b,d] Recently,the highly reactive singlet oxygen ( 1 D g or 1 O 2 )w as shown to cause al arge fraction of the parasitic reactions;itforms at all stages of cycling at rates that resemble the rates of parasitic reactions. [4] Superoxide disproportionation to Li 2 O 2 was suggested as the source of 1 O 2 , which has been shown to react with electrolyte and carbon. [4a,5] Furthermore, 1 O 2 is now also recognized to contribute to interfacial reactivity of TMO intercalation materials.…”

An All Solid‐State Zinc−Air Battery with a Corrosion‐Resistant Air Electrode

“…[1][2][3][4][5][6][7] MetalÀair batteries are new generation batteries which are anticipated to contribute to long driving range per charge compared to conventional metal ion batteries. The efficient ionic communication between the half-cell electrodes provided by the Zirfon membrane in combination with the chemical/electrochemical stability of the TiN-based air electrode ultimately led to an all solid-state and air-breathing battery possessing high durability and stability.…”

“…[1][2][3][4][5][6][7] MetalÀair batteries are new generation batteries which are anticipated to contribute to long driving range per charge compared to conventional metal ion batteries. [1][2][3][4][5][6][7] MetalÀair batteries are new generation batteries which are anticipated to contribute to long driving range per charge compared to conventional metal ion batteries.…”