Fundamental interplay between anionic/cationic redox governing the kinetics and thermodynamics of lithium-rich cathodes

• Published in: Nature communications Vol. 8; no. 1; pp. 2219 - 12
• Main Authors: Assat, Gaurav, Foix, Dominique, Delacourt, Charles, Iadecola, Antonella, Dedryvère, Rémi, Tarascon, Jean-Marie
• Format: Journal Article
• Language: English
• Published: London Nature Publishing Group UK 20-12-2017; Nature Publishing Group; Nature Portfolio
• Subjects: 639/301/299; 639/638/161/891; Anions; Cathodes; Cations; Chemical Sciences; Electric potential; Electrochemistry; Humanities and Social Sciences; Hysteresis; Kinetics; Lithium; Lithium-ion batteries; Manganese; Mastering; Material chemistry; multidisciplinary; Other; Oxidation; Oxygen; Reaction kinetics; Rechargeable batteries; Science; Science (multidisciplinary); Thermodynamics; Voltage
• ISSN: 2041-1723; 2041-1723
• DOI: 10.1038/s41467-017-02291-9

Reversible anionic redox has rejuvenated the search for high-capacity lithium-ion battery cathodes. Real-world success necessitates the holistic mastering of this electrochemistry’s kinetics, thermodynamics, and stability. Here we prove oxygen redox reactivity in the archetypical lithium- and manganese-rich layered cathodes through bulk-sensitive synchrotron-based spectroscopies, and elucidate their complete anionic/cationic charge-compensation mechanism. Furthermore, via various electroanalytical methods, we answer how the anionic/cationic interplay governs application-wise important issues—namely sluggish kinetics, large hysteresis, and voltage fade—that afflict these promising cathodes despite widespread industrial and academic efforts. We find that cationic redox is kinetically fast and without hysteresis unlike sluggish anions, which furthermore show different oxidation vs. reduction potentials. Additionally, more time spent with fully oxidized oxygen promotes voltage fade. These fundamental insights about anionic redox are indispensable for improving lithium-rich cathodes. Moreover, our methodology provides guidelines for assessing the merits of existing and future anionic redox-based high-energy cathodes, which are being discovered rapidly.
Anionic redox chemistry has enabled the design of high-capacity battery cathodes for energy storage. Here, the authors demonstrate reversible anionic redox in an archetypical lithium-rich oxide via bulk-sensitive spectroscopies, further revealing its crucial role in practically important properties.