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

• Published in: Small science Vol. 4; no. 10
• Main Authors: Jodlbauer, Anna, Hogrefe, Katharina, Gadermaier, Bernhard, Wilkening, H. Martin R.
• Format: Journal Article
• Language: English
• Published: Weinheim John Wiley & Sons, Inc 01.10.2024; Wiley-VCH
• Subjects: Annealing; composites; Conductivity; Emissions; Energy storage; Greenhouse gases; ion dynamics; lithium sulfide; NMR; Nuclear magnetic resonance; Solid solutions; Spectrum analysis; Sulfur; Temperature
• ISSN: 2688-4046; 2688-4046
• DOI: 10.1002/smsc.202400199

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$\left(\text{Li}\right)_{2} \text{S}$ has not been fully understood yet. While nanocrystalline Li2S$\left(\text{Li}\right)_{2} \text{S}$ shows enhanced ion dynamics compared to its coarse‐grained counterpart, the interaction of Li2S$\left(\text{Li}\right)_{2} \text{S}$ with another binary such as LiI seems to be rather unexplored. Herein, an equimolar mixture of Li2S$\left(\text{Li}\right)_{2} \text{S}$ 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$^{6,7} \text{Li}$ 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$\left(\text{Li}\right)_{2} \text{S}$‐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$\left(\text{Li}\right)_{2} \text{S}$‐LiI. Mixtures of Li2S and LiI, if present in a nanocrystalline form, show ionic conductivities exceeding that of nanostructured (single phase) Li2S by two orders of magnitude. Nuclear magnetic resonance (NMR) spin‐lattice relaxation measurements sense the same huge change in Li diffusivity. Herein, 1D and 2D Li exchange NMR is used to understand how Li+ exchange occurs between the magnetically distinct Li environments.