Preventing Structural Rearrangements on Battery Cycling: A First-Principles Investigation of the Effect of Dopants on the Migration Barriers in Layered Li<sub>0.5</sub>MnO<sub>2</sub>

Layered LiMnO<sub>2</sub> is a potential Li ion cathode material that is known to undergo a layered to spinel transformation upon delithiation, as a result of Mn migration. A common strategy to improve the structural stability of LiMnO<sub>2</sub> has been to replace Mn with a range of metal dopants, although the mechanism by which each dopant stabilizes the structure is not well understood. In this work we characterize ion-migration barriers using hybrid eigenvector-following (EF) and density functional theory to study how trivalent dopants (Al<sup>3+</sup>, Cr<sup>3+</sup>, Fe<sup>3+</sup>, Ga<sup>3+</sup>, Sc<sup>3+</sup>, and In<sup>3+</sup>) affect Mn migration during the initial stage of the layered to spinel transformation in Li<sub>0.5</sub>MnO<sub>2</sub>. We demonstrate that dopants with small ionic radii, such as Al<sup>3+</sup> and Cr<sup>3+</sup>, can increase the barrier for migration, but only when they are located in the first cation coordination sphere of Mn. We also demonstrate how the hybrid EF approach can be used to study the migration barriers of dopant species within the structure of Li<sub>0.5</sub>MnO<sub>2</sub> efficiently. The transition state searching methodology described in this work will be useful for studying the effects of dopants on structural transformation mechanisms in a wide range of technologically interesting energy materials.