Lithium metal self-diffusion is too slow to sustain large
current
densities at the interface with a solid electrolyte, and the resulting
formation of voids on stripping is a major limiting factor for the
power density of solid-state cells. The enhanced morphological stability
of some lithium alloy electrodes has prompted questions on the role
of lithium diffusivity in these materials. Here, the lithium diffusivity
in Li-Mg alloys is investigated by an isotope tracer method, revealing
that the presence of magnesium slows down the diffusion of lithium.
For large stripping currents the delithiation process is diffusion-limited,
hence a lithium metal electrode yields a larger capacity than a Li-Mg
electrode. However, at lower currents we explain the apparent contradiction
that more lithium can be extracted from Li-Mg electrodes by showing
that the alloy can maintain a more geometrically stable diffusion
path to the solid electrolyte surface so that the effective lithium
diffusivity is improved.
The temperature coefficients of the resistivity (TCR) of Cu, Ru, Co, Ir, and W thin films have been investigated as a function of film thickness below 10 nm. Ru, Co, and Ir show bulk-like TCR values that are rather independent of the thickness, whereas the TCR of Cu increases strongly with the decreasing thickness. Thin W films show negative TCR values, which can be linked to high disorder. The results are qualitatively consistent with a temperature-dependent semiclassical thin-film resistivity model that takes into account phonon, surface, and grain boundary scattering. The results indicate that the thin-film resistivity of Ru, Co, and Ir is dominated by grain boundary scattering, whereas that of Cu is strongly influenced by surface scattering.
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