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Jahn-Teller Distortions and Phase Transitions in LiNiO2: Insights from Ab Initio Molecular Dynamics and Variable-Temperature X-ray Diffraction.

Published version
Peer-reviewed

Repository DOI


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Authors

Genreith-Schriever, Annalena R  ORCID logo  https://orcid.org/0000-0001-5626-2438
Alexiu, Alexandra 
Phillips, George S 
Coates, Chloe S 
Nagle-Cocco, Liam AV  ORCID logo  https://orcid.org/0000-0001-9265-1588

Abstract

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. The common consensus is that the material exhibits local Jahn-Teller distortions that dynamically reorient, resulting in a time-averaged undistorted R3̅m structure. 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. Static Jahn-Teller distortions are observed at low temperatures (T < 250 K) via AIMD simulations, followed by a broad phase transition that occurs between 250 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. These transitions are followed in the AIMD simulations via abrupt changes in the calculated pair distribution function and the bond-length distortion index and in X-ray diffraction via the monoclinic lattice parameter ratio, amon/bmon, and δ angle, the fit quality of an R3̅m-based structural refinement, and a peak sharpening of the diffraction peaks on heating, consistent with the loss of distorted domains. Between 250 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 are 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.

Description

Publication status: Published

Keywords

34 Chemical Sciences, 3406 Physical Chemistry

Journal Title

Chem Mater

Conference Name

Journal ISSN

0897-4756
1520-5002

Volume Title

36

Publisher

American Chemical Society (ACS)
Sponsorship
Faraday Institution (via University of Oxford) (FIRG063)
Faraday Institution (FIRG016)
Faraday Institution (via University Of Bath) (FIRG016)
Faraday Institution (via University Of Bath) (FIRG016)
Faraday Institution (FIRG016)
Faraday Institution (via University of Oxford) (CATMAT)
Faraday Institution (FIRG024)
Faraday Institution (Unknown)
Faraday Institution (FIRG001)
Faraday Institution (Unknown)
European Commission Horizon 2020 (H2020) Research Infrastructures (RI) (957189)
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, Euan N. Bassey, 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).