Ion Dynamics in Nanocrystalline Li2S‐LiI – on the Influence of Local Disorder on Short‐Range Hopping and Long‐Range Ion Transport

Abstract

The enormous interest in developing powerful Li‐based batteries leads to a boost in materials research. Though Li–sulfur batteries offer very high energy densities, the nature of Li‐ion dynamics in the final discharge product Li2S has not been fully understood yet. While nanocrystalline Li2S shows enhanced ion dynamics compared to its coarse‐grained counterpart, the interaction of Li2S with another binary such as LiI seems to be rather unexplored. Herein, an equimolar mixture of Li2S and LiI is treated in a high‐energy ball mill, and both the overall and local structural changes are studied by X‐ray powder diffraction and 6,7Li nuclear magnetic resonance (NMR), respectively . Besides the formation of amorphous regions, evidences are found for the generation of anion‐mixed sites that give rise to facile Li+ exchange on the 2D exchange NMR timescale. Compared to a coarse‐grained reference sample, the overall (bulk) ionic conductivity of nanocrystalline Li2S‐LiI increases by two orders of magnitude. Besides the anion‐mixing effect, this increase benefits from nanosize effects that include the formation of defect‐rich interfacial regions. NMR relaxation measurements fully support this result and reveal heterogeneous dynamics with lower activation energies for both the localized hopping processes and long‐range ion transport in nm‐sized Li2S‐LiI.

Keywords

• composites
• conductivity
• ion dynamics
• lithium sulfide
• nuclear magnetic resonance