Mapping Structural Changes in Electrode Materials:
Application of the Hybrid Eigenvector-Following Density Functional
Theory (DFT) Method to Layered Li<sub>0.5</sub>MnO<sub>2</sub>
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Abstract
The migration mechanism associated
with the initial layered-to-spinel
transformation of partially delithiated layered LiMnO<sub>2</sub> was
studied using hybrid eigenvector-following coupled with density functional
theory. The initial part of the transformation mechanism of Li<sub>0.5</sub>MnO<sub>2</sub> involves the migration of Li into both octahedral
and tetrahedral local minima within the layered structure. The next
stage of the transformation process involves the migration of Mn and
was found to occur through several local minima, including an intermediate
square pyramidal MnO<sub>5</sub> configuration and an independent
Mn<sup>3+</sup> to Mn<sup>2+</sup> charge-transfer process. The migration
pathways were found to be significantly affected by the size of the
supercell used and the inclusion of a Hubbard U parameter in the DFT
functional. The transition state searching methodology described should
be useful for studying the structural rearrangements that can occur
in electrode materials during battery cycling, and more generally,
ionic and electronic transport phenomena in a wide range of energy
materials