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- Title
Transition metal migration and O<sub>2</sub> formation underpin voltage hysteresis in oxygen-redox disordered rocksalt cathodes.
- Authors
McColl, Kit; House, Robert A.; Rees, Gregory J.; Squires, Alexander G.; Coles, Samuel W.; Bruce, Peter G.; Morgan, Benjamin J.; Islam, M. Saiful
- Abstract
Lithium-rich disordered rocksalt cathodes display high capacities arising from redox chemistry on both transition-metal ions (TM-redox) and oxygen ions (O-redox), making them promising candidates for next-generation lithium-ion batteries. However, the atomic-scale mechanisms governing O-redox behaviour in disordered structures are not fully understood. Here we show that, at high states of charge in the disordered rocksalt Li2MnO2F, transition metal migration is necessary for the formation of molecular O2 trapped in the bulk. Density functional theory calculations reveal that O2 is thermodynamically favoured over other oxidised O species, which is confirmed by resonant inelastic X-ray scattering data showing only O2 forms. When O-redox involves irreversible Mn migration, this mechanism results in a path-dependent voltage hysteresis between charge and discharge, commensurate with the hysteresis observed electrochemically. The implications are that irreversible transition metal migration should be suppressed to reduce the voltage hysteresis that afflicts O-redox disordered rocksalt cathodes. The oxygen-redox mechanism in lithium-rich disordered rocksalt cathode materials is still not well understood. Here, the authors show that in Li2MnO2F, molecular oxygen forms in the bulk during charge and is re-incorporated into the structure as oxygen anions on discharge, but this process is associated with irreversible Mn migration, causing voltage hysteresis.
- Subjects
TRANSITION metals; CATHODES; VOLTAGE; INELASTIC scattering; DENSITY functional theory; X-ray scattering; HYSTERESIS
- Publication
Nature Communications, 2022, Vol 12, Issue 1, p1
- ISSN
2041-1723
- Publication type
Article
- DOI
10.1038/s41467-022-32983-w