Phase segregation and nanoconfined fluid O 2 in a layered lithium rich oxide cathode material Kit McColl 1 , Pezhman Zarabadi-Poor 2,3 , Samuel W Coles 1,2,3, Benjamin J. Morgan 1,2 and M. Saiful Islam 1,2,3 1 University of Bath, UK, 2 The Faraday Institution, Didcot, UK, 3 Department of Materials, University of Oxford, UK High-capacity lithium-rich oxide cathodes lose energy density during cycling due to detrimental structural changes.[1,2] The atomic-scale origins of these structural changes, however, are not well characterised. Here, we use ab initio molecular dynamics and a cluster expansion to elucidate these structural changes and the oxygen-redox mechanisms in an exemplar layered Li-rich cathode, O2–Li 1.2–x Mn 0.8 O 2 . We identify a kinetically favourable mechanism to form stable O 2 molecules in the bulk,[3] involving Mn migration, driven by interlayer oxygen dimerisation. At the top of charge, the bulk structure locally phase-segregates into MnO 2 -rich regions, and Mn-deficient nanovoids containing O 2 molecules. The O 2 is a high density nanoconfined fluid, and the nanovoids form a connected, percolating network, enabling oxygen transport through the cathode. This work provides new atomic-level and nanoscale insight into the complex electrochemistry of Li-rich oxide cathodes and has wide implications for understanding structural rearrangements in battery cathode materials. References 1. Assat, G. & Tarascon, J.-M. Fundamental understanding and practical challenges of anionic redox activity in Li-ion batteries. Nat. Energy 3, 373–386 (2018) 2. McColl, K. et al. Transition metal migration and O2 formation underpin voltage hysteresis in oxygen-redox disordered rocksalt cathodes. Nat. Commun. 13, 5275 (2022) 3. House, R. A. et al. The role of O2 in O-redox cathodes for Li-ion batteries. Nat. Energy (2021)
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© The Author(s), 2021
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