Towards controlling the reversibility of anionic redox in transition metal oxides for high-energy Li-ion positive electrodes

• Published in: Energy & environmental science 2021-04, Vol.14 (4), p.2322-2334
• Main Authors: Yu, Yang, Karayaylali, Pinar, Sokaras, Dimosthenis, Giordano, Livia, Kou, Ronghui, Sun, Cheng-Jun, Maglia, Filippo, Jung, Roland, Gittleson, Forrest S, Shao-Horn, Yang
• Format: Article
• Language: English
• Subjects: Absorption spectroscopy; Chromium; Density functional theory; Dimers; Electrochemistry; Electrode materials; Electrodes; Flux density; High-throughput screening; Infrared spectroscopy; Lithium-ion batteries; Manganese; Mass spectrometry; Mass spectroscopy; Metals; Oxygen; Rechargeable batteries; Titanium; Transition metal oxides; X ray absorption; X-ray absorption spectroscopy
• ISSN: 1754-5692; 1754-5706
• DOI: 10.1039/d0ee03765f

Anionic redox in positive electrode materials in Li-ion batteries provides an additional redox couple besides conventional metal redox, which can be harvested to further boost the energy density of current Li-ion batteries. However, the requirement for the reversible anionic redox activity remains under debate, hindering the rational design of new materials with reversible anionic redox. In this work, we employed differential electrochemical mass spectrometry (DEMS) to monitor the release of oxygen and to quantify the reversibility of the anionic redox of Li 2 Ru 0.75 M 0.25 O 3 (M = Ti, Cr, Mn, Fe, Ru, Sn, Pt, Ir) upon first charge. X-ray absorption spectroscopy, coupled with density functional theory (DFT) calculations, show that various substituents have a minimal effect on the nominal metal redox, yet more ionic substituents and reduced metal-oxygen covalency introduce irreversible oxygen redox, accompanied with easier distortion of the M-O octahedron and a smaller barrier for forming an oxygen dimer within the octahedron. Therefore, a strong metal-oxygen covalency is needed to enhance the reversible oxygen redox. We proposed an electron-phonon-coupled descriptor for the reversibility of oxygen redox, laying the foundation for high-throughput screening of novel materials that enable reversible anionic redox activity. Transition metal d-states and oxygen p-states overlap and oxygen lattice integrity dictates the oxygen redox reversibility in metal substituted Li 2 RuO 3 positive electrodes for Li-ion batteries.