Spectroscopic Signature of Oxidized Oxygen States in Peroxides

TL;DR

This study uses advanced mRIXS techniques and first-principles calculations to identify unique spectroscopic signatures of oxidized oxygen states in peroxides, aiding in understanding oxygen redox in battery materials.

Contribution

It introduces a reliable method to detect oxidized oxygen states in peroxides using mRIXS, distinguishing them from other features in absorption spectra.

Findings

mRIXS features of oxygen states in Li2O, Li2CO3, Li2O2 identified

Oxidized oxygen in Li2O2 shows a unique intra-band excitonic feature

Method helps disentangle oxygen redox signals from transition-metal/oxygen hybridization

Abstract

Recent debates on the oxygen redox behaviors in battery electrodes have triggered a pressing demand for the reliable detection and understanding of non-divalent oxygen states beyond conventional absorption spectroscopy. Here, enabled by high-efficiency mapping of resonant inelastic X-ray scattering (mRIXS) coupled with first-principles calculations, we report distinct mRIXS features of the oxygen states in Li2O, Li2CO3, and especially, Li2O2, which are successfully reproduced and interpreted theoretically. mRIXS signals are dominated by valence-band decays in Li2O and Li2CO3. However, the oxidized oxygen in Li2O2 leads to partially unoccupied O-2p states that yield a specific intra-band excitonic feature in mRIXS. Such a feature displays a specific emission energy in mRIXS, which disentangles the oxidized oxygen states from the dominating transition-metal/oxygen hybridization features in absorption spectroscopy, thus providing critical hints for both detecting and understanding the oxygen redox reactions in transition-metal oxide based battery materials.