Oxygen-redox Chemistry in High Energy Density Battery Cathodes

Robert House^a, John-Joseph Marie^a, Miguel Perez-Osorio^a, Gregory Rees^a, Mikkel Juelsholt^a, Jun Chen^a, Peter Bruce^a

^aDepartment of Materials, University of Oxford; Oxford, UK

Proceedings of 24th International Conference on Solid State Ionics (SSI24)

Devices for a Net Zero World

London, United Kingdom, 2024 July 14th - 19th

Organizers: John Kilner and Stephen Skinner

Invited Speaker, Robert House, presentation 038
Publication date: 10th April 2024

One of the biggest challenges facing lithium-ion batteries is how to increase their energy density. The cathode, typically a layered lithium transition metal oxide, represents a major limitation. One route to increase the energy density is to store charge at high voltage on the oxide ions in the cathode material. However, removing electrons from lattice oxide ions typically results in structural instability leading to voltage hysteresis and voltage fade over cycling. Understanding the mechanism behind oxygen redox is critical to overcoming these issues.

Our recent investigations into Li-rich cathodes have revealed that oxidized oxygen takes the form of O₂ molecules which are trapped in nanovoids in the structure. We have also shown that these trapped O₂ molecules can be reduced back to O^2- on discharge providing a viable charge storage mechanism to explain oxygen redox. In this talk, I will discuss the evidence for the formation and reduction of trapped O₂ [1-3] and explore the impacts this has on the performance of oxygen redox cathodes[4]. I will show how the formation of O₂ extends to 4d and 5d transition metal oxides[5], disordered rocksalt cathodes[6] and even to non-Li-rich cathodes[7]. Finally, I will show that it is possible to suppress this structural change and undergo reversible, high voltage O-redox without voltage hysteresis[8]. Altogether, this understanding helps to explain the unusual properties of oxygen redox cathodes and informs how they might be harnessed to boost the energy density of batteries.

References:

[1] House R. A., Maitra, U., Perez-Osorio, M. A., Lozano, J. G., Jin, L., Somerville, J. W., Duda, L. C., Nag, A., Walters, A., Zhou, K-J., Roberts, M. R., Bruce, P. G. Superstructure Controls First Cycle Voltage Hysteresis in O-redox Cathodes for Alkali-ion Batteries, Nature, 2020, 577, 502–508.

[2] House R. A., Rees, G. J., Perez-Osorio, M. A., Marie, J-J., Boivin, E., Robertson, A. W., Nag, A., Garcia-Fernandez, M., Zhou, K-J., Bruce, P. G. First-cycle voltage hysteresis in Li-rich 3d cathodes associated with molecular O2 trapped in the bulk, Nature Energy, 2020, 5, 777–785.

[3] House, R. A., Playford, H. Y., Smith, R. I., Holter, J., Griffiths, I., Zhou, K., Bruce P. G., Detection of trapped molecular O2 in a charged Li-rich cathode by Neutron PDF, Energy & Environmental Science, 2022, 15, 376-383.

[4] House, R. A., Marie, J-J., Perez-Osorio, M. A., Rees, G. J., Boivin, E., Bruce P.G., The Role of O2 in O-redox Cathodes, Nature Energy, 2021, 6, 781-789.

[5] House, R. A., Marie, J-J., Park J., Agrestini, S., Nag, A., Garcia-Fernandez, M., Zhou K-J., Bruce P. G., Covalency Does Not Suppress O2 Formation in 4d and 5d Li-rich O-redox Cathodes, Nature Communications, 2021, 12, 2975

[6] McColl, K., House, R. A., Rees, G. J., Squires, A. G., Coles, S. W., Bruce, P. G., Morgan, B. J., Islam, M. S., Transition metal migration and O2 formation underpin voltage hysteresis in oxygen-redox disordered rocksalt cathodes, Nature Communications, 2022, 13, 1, 1-8

[7] Juelsholt, M., Chen, J., Perez-Osorio, M. A., Rees, G. J., De Sousa Coutinho, S., Maynard-Casely, H. E., Liu, J., Everett, M., Agrestini, S., Garcia-Fernandez, M., Zhou, K-J., House, R. A., Bruce, P. G., Does trapped O2 form in the bulk of LiNiO2 during charging?, ChemRxiv

[8] House, R. A., Rees, G. J., McColl, K., Marie, J-J., Garcia-Fernandez, M., Nag, A., Zhou K-J., Cassidy, S., Morgan, B. J., Islam, M. S., Bruce, P. G., Delocalised electron-holes on oxygen in a battery cathode, Nature Energy, 2023, 8, 4, 351-360

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