SCIENCE SPIN-OFFS

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Interfacial Strain Effects on Lithium Diffusion Pathways in the Spinel Solid Electrolyte Li-Doped MgAl2O4

Conn O'Rourke, Benjamin J. Morgan
(Submitted on 6 Dec 2017)

Here we report a density functional theory study of strain effects on lithium diffusion pathways for (Li,Al)-co-doped magnesium spinel, for
x
Li
=0.25
and
x
Li
=0.5
. We have calculated diffusion profiles for the unstrained materials, and for isotropic and biaxial tensile strains of up to 6%, corresponding to {100} epitaxial interfaces with Li

y
Mn

2
O

4
and Li

4+3z
Ti

5
O

12
. We find that isotropic tensile strain reduces lithium diffusion barriers from ~ 0.4 eV by as much as 0.28 eV, with typical barriers reduced by ~ 0.15 eV. This effect is associated with increased volumes of transitional octahedral sites, and broadly follows qualitative changes in local electrostatic potentials. For biaxial (epitaxial) strain, which more closely approximates strain at a lattice-matched electrolyte-electrode interface, changes in octahedral site volumes and in lithium diffusion barriers are much smaller than under isotropic strain. These results predict that isotropic strain strongly affects ionic conductivities in (Li,Al)-co-doped magnesium spinel electrolytes, and that tensile strain is a potential route to enhanced lithium transport. For a lattice-matched interface with candidate spinel-structured electrodes, however, epitaxial strain has only a small effect on lithium diffusion barriers. From the perspective of local diffusion barriers, therefore, epitaxial strain at coherent lattice-matched electrolyte-electrode interfaces is therefore not expected to strongly affect lithium transport rates or overall cell performance.


https://arxiv.org/abs/1712.02156