Mg Intercalation in Layered and Spinel Host Crystal
Structures for Mg Batteries
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Abstract
We investigate electrochemical properties
of Mg in layered and spinel intercalation compounds from first-principles
using TiS<sub>2</sub> as a model system. Our calculations predict
that Mg<sub><i>x</i></sub>TiS<sub>2</sub> in both the layered
and spinel crystal structures exhibits sloping voltage profiles with
steps at stoichiometric compositions due to Mg-vacancy ordering. Mg
ions are predicted to occupy the octahedral sites in both layered
and spinel TiS<sub>2</sub> with diffusion mediated by hops between
octahedral sites that pass through adjacent tetrahedral sites. Predicted
migration barriers are substantially higher than typical Li-migration
barriers in intercalation compounds. The migration barriers are shown
to be very sensitive to lattice parameters of the host crystal structure.
We also discuss the possible role of rehybridization between the transition
metal and the anion in affecting migration barriers