# Temperature-dependent dynamic disproportionation in LiNiO2

## TL;DR

This study reveals how nickel ions in lithium nickel oxide dynamically change states with temperature, explaining the material's properties and potential uses.

## Contribution

The paper introduces a model of dynamic nickel ion disproportionation in LiNiO2, verified by experiments and simulations.

## Key findings

- Ni ions in LiNiO2 disproportionate into three states that interconvert dynamically.
- Temperature affects the population of these nickel states, influencing material properties.
- The model explains various physical behaviors like magnetism and electronic conduction.

## Abstract

Nickelate materials offer diverse functionalities for energy and computing applications. Lithium nickel oxide (LiNiO2) is an archetypal layered nickelate, but the electronic structure of this correlated material is not yet fully understood. Here we investigate the temperature-dependent speciation and spin dynamics of Ni ions in LiNiO2. Ab initio simulations predict that Ni ions disproportionate into three states, which dynamically interconvert and whose populations vary with temperature. These predictions are verified using x-ray absorption spectroscopy, x-ray magnetic circular dichroism, and resonant inelastic x-ray scattering at the Ni L3,2-edge. Charge-transfer multiplet calculations consistent with disproportionation reproduce all experimental features. Our results support a model of dynamic disproportionation that explains diverse physical observations of LiNiO2, including magnetometry, thermally activated electronic conduction, diffractometry, core-level spectroscopies, and the stability of ubiquitous antisite defects. This unified understanding of the material properties of LiNiO2 is important for applications of nickelate materials as battery cathodes, catalysts, and superconductors.

A dynamic interconversion of three nickel states in lithium nickel oxide is demonstrated using evidence from x-ray spectroscopic data and first-principles calculations, which explains many physical properties of this and similar materials.