Transition metal migration and O2 formation underpin voltage hysteresis in oxygen-redox disordered rocksalt cathodes

Kit McColl, Robert A. House, Gregory J Rees, Alex Squires, Samuel Coles, Peter G Bruce, Benjamin Morgan, MS Islam

Research output: Contribution to journalArticlepeer-review

Abstract

Lithium-rich disordered rocksalt cathodes display high capacities arising from redox chemistry on both transition-metal and oxygen ions and are potential candidates for next-generation lithium-ion batteries. The atomic-scale mechanisms governing this O-redox behaviour, however, are not fully understood. In particular, it is not clear to what extent transition metal migration is required for O-redox and what role this may play in explaining voltage hysteresis in these materials. Here, we reveal an O-redox mechanism linking transition metal migration and O2 formation in the disordered rocksalt Li2MnO2F. At high states of charge, O-ions dimerise to form molecular O2 trapped in the bulk structure, leaving vacant O sites surrounding neighbouring Mn ions. This undercoordination drives Mn movement into new fully-coordinated octahedral sites. Mn displacement can occur irreversibly, which results in voltage hysteresis, with a lower voltage upon discharge as observed experimentally. Alternatively, Mn displacement may take place into interstitial octahedral sites, which permits a reversible return of the Mn ion to its original site upon discharge, recovering the original Li2MnO2F structure and resulting in reversible O-redox without voltage loss. These new findings suggest that reversible transition metal ion migration provides a possible design route to retain the high energy density of O-redox disordered rocksalt cathodes on cycling.
Original languageEnglish
JournalNature Communications
Volume13
DOIs
Publication statusPublished - 7 Sept 2022

Bibliographical note

The authors thank the Faraday Institution CATMAT project (EP/S003053/1, FIRG016) and the Henry Royce Institute for financial support. We are also grateful to the HEC Materials Chemistry Consortium (EP/R029431) for Archer high-performance computing (HPC) facilities, GW4 and the UK Met Office for access to the Isambard HPC Service (EP/P020224/1) and for the Faraday Institution’s MICHAEL HPC resource. K.M. and A.G.S. thank Dr Stefano Angioni for access to HPC resources through the University of Bath’s Cloud Computing Pilot Project. A.G.S. thanks the STFC Batteries Network for an Early Career Researcher Award (ST/R006873/1). This project was supported by the Royal Academy of Engineering under the Research Fellowship scheme. B.J.M. acknowledges support from the Royal Society (URF\R\191006). We acknowledge Diamond Light Source for time on I21 under proposal MM29028-1.

Data availability
The datasets generated during and/or analysed during the current study are available in the University of Bath repository (https://doi.org/10.15125/BATH-01189).

Fingerprint

Dive into the research topics of 'Transition metal migration and O2 formation underpin voltage hysteresis in oxygen-redox disordered rocksalt cathodes'. Together they form a unique fingerprint.

Cite this