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>
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Abstract
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
