Jahn–Teller Distortions and Phase Transitions in LiNiO 2 : Insights from Ab Initio Molecular Dynamics and Variable-Temperature X-ray Diffraction

作者：Annalena R. Genreith‐Schriever, Alexandra Alexiu, George Searle Phillips, Chloe Coates, Liam A. V. Nagle‐Cocco, Joshua D. Bocarsly, Farheen N. Sayed, Siân E. Dutton, Clare P. Grey · 发表于：Chemistry of Materials · 年份：2024 · DOI：10.1021/acs.chemmater.3c02413 · 被引用次数：51 · 研究领域：Advancements in Battery Materials、X-ray Diffraction in Crystallography、Electron and X-Ray Spectroscopy Techniques

High Resolution Image Download MS PowerPoint Slide The atomistic structure of lithium nickelate (LiNiO 2 ), 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 R 3̅ m 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 LiNiO 2 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, a mon / b mon, and δ angle, the fit quality of an R 3̅ m -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 coexis...