Full Energy Range Resonant Inelastic X-ray Scattering of O and CO: Direct Comparison with Oxygen Redox State in Batteries.

The evolving oxygen state plays key roles in the performance and stability of high-energy batteries involving oxygen redox reactions. Here, high-efficiency full energy range O mapping of resonant inelastic X-ray scattering (mRIXS) was collected from O (O) and CO (O with strong covalency) molecules and compared directly with LiO (O) and the oxidized oxygen state in representative Na/Li-ion battery electrodes. Our results confirm again that the critical mRIXS feature around the 523.7 eV emission energy is from intrinsically oxidized oxygen, but not from the highly covalent oxygen state (CO). The comparison of the mRIXS profile of the four different oxygen states, i.e., O, O, O (0 < < 2), and O, reveals that oxygen redox states in batteries have distinct widths and positions along the excitation energy compared with LiO and O. The nature of the oxidized oxygen state in oxide electrodes is thus beyond a simple molecular configuration of either peroxide or O.