Probing Jahn-Teller Distortions and Antisite Defects in LiNiO2 with Ab-initio Molecular Dynamics, Variable-Temperature X-Ray Diffraction, and 7Li NMR Spectroscopy

Annalena R. Genreith-Schriever^a^,^h, Alexandra Alexiu^a, Chloe S. Coates^a^,^h, George S. Phillips^a^,^h, Liam A. V. Nagle-Cocco^b^,^h, Joshua D. Bocarsly^a^,^c^,^h, Farheen N. Sayed^a^,^h, Katharina Märker^a^,^d^,^h, Ieuan D. Seymour^e^,^f^,^g^,^h, Euan N. Bassey^a, Sian E. Dutton^b^,^h, Clare P. Grey^a^,^h

^aYusuf Hamied Department of Chemistry, University of Cambridge, Lensfield Road, CB2 1EW, Cambridge, UK

^bDepartment of Physics, Cavendish Laboratory, University of Cambridge, Cambridge CB3 0HE, U.K.

^cDepartment of Chemistry, University of Houston, Houston, TX, 77204, US

^dUniv. Grenoble Alpes, CEA, IRIG, MEM; 17 Avenue des Martyrs Grenoble, 38054, FR

^eImperial College London, Department of Materials, London, London, SW7 2AZ, UK

^fUniversity of Aberdeen, Department of Chemistry, Aberdeen, AB24 3FX, UK

^gUniversity of Aberdeen, Advanced Centre for Energy and Sustainability, Aberdeen, AB24 3FX, UK

^hThe Faraday Institution, Didcot, England, OX11 0RA, UK

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

Fundamentals: Experiment and simulation

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

Organizers: John Kilner and Stephen Skinner

Oral, Annalena R. Genreith-Schriever, presentation 404
Publication date: 10th April 2024

The atomistic structure of lithium nickelate (LiNiO₂), the parent compound of Ni-rich layered oxide cathodes for Li-ion batteries, continues to elude a comprehensive understanding. In particular, the local structural environment and the role of Jahn-Teller distortions are unclear, as are the interplay of distortions and point defects, and their influence on cycling behaviour. Through a combination of ab initio molecular dynamics (AIMD) simulations and variable-temperature X-ray diffraction (VT-XRD), we explore Jahn-Teller distortions in LiNiO₂ as a function of temperature.[1] Static Jahn-Teller distortions are observed at low temperatures (T < 250 K), followed by a broad phase transition occurring between 250 K and 350 K, leading to a highly dynamic, displacive phase at high temperatures (T > 350 K), which does not show the four short and two long bonds characteristic of local Jahn-Teller distortions. Between 250 K and 350 K, a mixed-phase regime is found via the AIMD simulations where distorted and undistorted domains coexist. The repeated change between the distorted and undistorted states in this mixed phase regime allows the Jahn-Teller long axes to change direction, these pseudorotations of the Ni-O long axes being a side effect of the onset of the displacive phase transition. Antisite defects, involving Li ions in the Ni layer and Ni ions in the Li layer, are found to pin the undistorted domains at low temperatures, impeding cooperative ordering at a longer length scale. Using ⁷Li NMR measurements in combination with density functional theory (DFT) calculations, we predict the ⁷Li Fermi contact shifts for the Jahn-Teller distorted and undistorted structures, the experimental ⁷Li room temperature spectrum being ascribed to an appropriately weighted time-average of the rapidly fluctuating structure comprising, collinear, zigzag and undistorted domains. The ⁷Li NMR spectra are sensitive to the nature and distribution of anti-site defects, and in combination with DFT calculations we identify ⁷Li resonances characteristic of specific antisite-defect configurations.

References:

[1] Genreith-Schriever, A. R.; Alexiu, A.; Phillips, G. S.; Coates, C. S.; Nagle-Cocco, L. A. V.; Bocarsly, J. D.; Sayed, F. N.; Dutton, S. E.; Grey, C. P. Jahn-Teller distortions and phase transitions in LiNiO2: Insights from ab initio molecular dynamics and variable-temperature X-ray diffraction. Chem. Mater., accepted,

Acknowledgements:

This work was supported by the Faraday Institution degradation project (FIRG011, FIRG020) and CATMAT project (FIRG016). This project has received funding from the European Union’s Horizon 2020 research and innovation program under grant agreement No 957189 (BIGMAP). The project is part of BATTERY 2030+, the large-scale European research initiative for inventing the sustainable batteries of the future, funded by the European Union's Horizon 2020 research and innovation program under Grant Agreement No. 957213. PXRD measurements were performed at the I11 beamline at Diamond Light Source, for which the authors acknowledge the award of a Block Allocation Grant (CY28349). A.R.G.-S. gratefully acknowledges funding from the German National Academy of Sciences Leopoldina. L.N.C. acknowledges a scholarship EP/R513180/1 to pursue doctoral research from the UK Engineering and Physical Sciences Research Council (EPSRC). We thank Samuel P. Niblett, Teresa Insinna, Andrey D. Poletayev, Hrishit Banerjee, and Andrew J. Morris for fruitful discussions. Generous computing resources were provided by the Sulis HPC service (EP/T022108/1).

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