# Reciprocal Space Imaging of Ionic Correlations in Intercalation Compounds

## TL;DR

This paper introduces a novel synchrotron x-ray technique to measure ionic correlations in intercalation compounds, revealing short-range order effects that impact battery performance.

## Contribution

It demonstrates a model-independent method using diffuse scattering to analyze ionic correlations in layered materials, advancing understanding of structural ordering.

## Key findings

- Measured temperature dependence of ionic correlation length scales.
- Revealed short-range ionic order not detectable by conventional diffraction.
- Provided a new approach for probing structural evolution in crystalline materials.

## Abstract

The intercalation of alkali ions into layered materials has played an essential role in battery technology since the development of the first lithium-ion electrodes. Coulomb repulsion between the intercalants leads to ordering of the intercalant sublattice, which hinders ionic diffusion and impacts battery performance. While conventional diffraction can identify the long-range order that can occur at discrete intercalant concentrations during the charging cycle, it cannot determine short-range order at other concentrations that also disrupt ionic mobility. In this article, we show that the use of real-space transforms of single crystal diffuse scattering, measured with high-energy synchrotron x-rays, allows a model-independent measurement of the temperature dependence of the length scale of ionic correlations along each of the crystallographic axes in a sodium-intercalated V$_2$O$_5$. The techniques described here provide a new way of probing the evolution of structural ordering in crystalline materials.