Li diffusion in Li$_x$CoO$_2$ probed by muon-spin spectroscopy

TL;DR

This study uses muon-spin relaxation to measure lithium ion diffusion in Li$_x$CoO$_2$, confirming diffusion behavior above 150 K and aligning well with theoretical predictions, demonstrating the technique's effectiveness.

Contribution

The paper introduces muon-spin relaxation as a novel and effective method to directly measure lithium diffusion coefficients in magnetic ion-containing materials.

Findings

Li$^+$ diffusion detected above 150 K

Diffusion coefficient agrees with first-principles calculations

Muon-spin relaxation is a suitable probe for magnetic materials

Abstract

The diffusion coefficient of Li$^+$ ions ($D_{\rm Li}$) in the battery material Li$_x$CoO$_2$ has been investigated by muon-spin relaxation ($\mu^+$SR). Based on the experiments in zero-field and weak longitudinal-fields at temperatures up to 400 K, we determined the fluctuation rate ($\nu$) of the fields on the muons due to their interaction with the nuclear moments. Combined with susceptibility data and electrostatic potential calculations, clear Li$^+$ ion diffusion was detected above $\sim150$K. The $D_{\rm Li}$ estimated from $\nu$ was in very good agreement with predictions from first-principles calculations, and we present the $\mu^+$SR technique as an % novel and optimal probe to detect $D_{\rm Li}$ for materials containing magnetic ions.