First-principles study on Small Polaron and Li diffusion in layered LiCoO2

TL;DR

This study uses density functional theory to analyze how polarons influence lithium-ion diffusion in layered LiCoO2, revealing the impact of magnetic orderings and electron correlations on diffusion barriers and polaron stability.

Contribution

It provides new insights into the role of magnetic configurations and electron correlations in polaron formation and Li diffusion in LiCoO2, which was not thoroughly understood before.

Findings

Polaron presence increases Li diffusion barrier to ~0.34 eV.

Magnetically ordered structures are more stable during migration.

Strong electron correlation stabilizes the Co4+ polaron.

Abstract

Li-ion conductivity is one of the essential properties that determine the performance of cathode materials for Li-ion batteries. Here, using the density functional theory, we investigate the polaron stability and its effect on the Li-ion diffusion in layered LiCoO2 with different magnetic orderings. The localized Co4+ polaron appears in the magnetic configurations and sets the Li-diffusion barrier of ~0.34 eV. The polaron also migrates in the opposite direction to the Li-diffusion direction. On the other hand, the polaron does not form in the non-magnetic structure, and the Li diffusion barrier without the polaron is 0.21 eV. Although the existence of the polaron increases the diffusion barrier, the magnetically ordered structures are more energetically stable during the migration than the non-magnetic case. Thus, our work advocates the hole polaron migration scenario for Li-ion diffusion. Moreover, we demonstrate that the strong electron correlation of Co ions plays an essential role in stabilizing the Co4+ polaron.