Whither Mn Oxidation in Mn-Rich Alkali-Excess Cathodes?

• Published in: ACS energy letters Vol. 6; no. 3; pp. 1055 - 1064
• Main Authors: Zuba, Mateusz Jan, Grenier, Antonin, Lebens-Higgins, Zachary, Fajardo, Galo J. Paez, Li, Yixuan, Ha, Yang, Zhou, Hui, Whittingham, M. Stanley, Yang, Wanli, Meng, Ying Shirley, Chapman, Karena W, Piper, Louis F. J
• Format: Journal Article
• Language: English
• Published: United States American Chemical Society 12.03.2021; American Chemical Society (ACS)
• Subjects: Diffraction; Genetics; INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY; Oxygen; Physical and chemical processes; Redox reactions; Transition metals
• ISSN: 2380-8195; 2380-8195
• DOI: 10.1021/acsenergylett.0c02418

Lithium-rich NMC (LR-NMC) compounds exhibit high capacities beyond the traditional redox, but it remains unclear whether the anomalous charge compensation mechanism is due to oxidized lattice oxygen or migration-assisted Mn oxidation. We compare LR-NMC with a model Mn7+ system (KMnO4) using a combination of resonant inelastic X-ray scattering (RIXS) irradiation studies and operando X-ray absorption spectroscopy/X-ray diffraction (XAS/XRD) to quantify transition metal (TM) migration, Mn oxidization, and beam-induced effects. We reveal how for KMnO4 it is possible to observe beam-induced Mn reduction resulting in trapped molecular oxygen. For LR-NMC, we observe negligible evidence for Mn oxidation while stabilized tetrahedral sites correlate more with a reduced TM environment. Finally, the additional spectroscopic structures observed in oxidized oxygen RIXS for LR-NMC are absent for gas-phase molecular oxygen.