Clarifying the origin of molecular O2 in cathode oxides

• Published in: Nature materials Vol. 24; no. 5; pp. 743 - 752
• Main Authors: Gao, Xu, Li, Biao, Kummer, Kurt, Geondzhian, Andrey, Aksyonov, Dmitry A., Dedryvère, Rémi, Foix, Dominique, Rousse, Gwenaëlle, Ben Yahia, Mouna, Doublet, Marie-Liesse, Abakumov, Artem M., Tarascon, Jean-Marie
• Format: Journal Article
• Language: English
• Published: London Nature Publishing Group UK 01.05.2025; Nature Publishing Group
• Subjects: 119/118; 140/146; 639/301/299/891; 639/638/161/891; Anions; Biomaterials; Cathodes; Chemical Sciences; Chemistry and Materials Science; Condensed Matter Physics; Decay; Dimerization; Electric potential; Electrochemistry; Electrode materials; Electrons; Excitation; Holes (electron deficiencies); Hysteresis; Inelastic scattering; Lithium-ion batteries; Materials Science; Nanotechnology; NMR; Nuclear magnetic resonance; Optical and Electronic Materials; Temperature effects; Voltage; X-ray scattering; Chemistry; Stability; Layered oxides; Capacity; Oxygen redbox activity; Challenges; LICOO2; Intercalation
• ISSN: 1476-1122; 1476-4660; 1476-4660
• DOI: 10.1038/s41563-025-02144-7

Anionic redox has reshaped the conventional way of exploring advanced cathode materials for Li-ion batteries. However, how anions participate in the redox process has been the subject of intensive debate, evolving from electron holes to O–O dimerization and currently to a focus on trapped molecular O 2 based on high-resolution resonant X-ray inelastic scattering research. Here we show that the resonant X-ray inelastic scattering signal of molecular O 2 is not exclusive to Li-rich oxide cathodes, but appears consistently in O-redox-inactive oxide materials even with a short beam exposure time as low as 1 min, indicating that molecular O 2 species are not directly related to voltage hysteresis and voltage decay. We further demonstrated that molecular O 2 is not a direct product of electrochemistry but more likely a consequence of the core excitation process in resonant X-ray inelastic scattering, for which the possible scenarios of the dissociation of ‘M-(O–O)’-like species on beam excitation must be considered. Collectively, our results reconcile the conflicting reported results on the (non-)observation of molecular O 2 signal collected from different beamlines and suggest that molecular O 2 is not the energetic engine of new battery oxide cathodes. Resonant inelastic X-ray scattering measurements suggest that the oxidized oxygen species in high-energy Li-rich oxide cathodes are trapped molecular O 2 , which is also observed in O-redox-inactive materials. This suggests that resonant X-ray inelastic scattering measurements generate these species, and molecular O 2 is not responsible for voltage hysteresis and decay.