Understanding Li Ions Diffusion in Sulphide- and Oxide-Based Ionic Conductors from NMR Spectroscopy

Li-containing materials providing fast Li ion transport pathways are fundamental in Li solid-state electrolytes and next-generation energy storage materials by implementing Li all-solid-state batteries. Collaborative computationally-guided materials discovery[1] has provided a workflow for identifying unexplored selection of elements containing Li ions[2,3]and designing new superionic Li solid-state electrolytes Li₇Si₂S₇I[4] (and derivatives)[5] defined by two-anion packing.<br/>Li ions transport is the key sought physical properties and, in this contribution, we will reveal several efficient NMR methods to probe directly the Li ions dynamics in a range of recently discovered sulphides[2-6] and oxides[7]-containing materials. We exploit a range of variable temperature multinuclear (⁶Li and ⁷Li) and multidimensional NMR approaches, such as line shape analysis, exchange phenomena, relaxometry measurements and spin-alignment echo, to determine the Li ion mobility pathways, including the dimensionality of the diffusion processes, and quantify Li ions jump rates. For example, these approaches deployed on (1): Li₃AlS₃[2] identify that Li ion diffusion is fast within the tetrahedral and tetrahedral/octahedral layers but slow between these layers limiting long range translational Li ion mobility;[8] these provide a framework for the further development of more highly conductive Li solid-state electrolytes such as Li_4.3AlS_3.3Cl_0.7;[6] (2) Li₃P₅O₁₄ determine that the low coordinating Li site exchange with one another between adjacent layered Li₆O₁₆^26- chains and through the centre of the P₁₂O₃₆^12- rings forming a three-dimensional Li diffusion pathway.<br/><br/>[1] C. Collins <i>et al.,</i> <i>Nature</i> <b>2017</b>, 280. [2] J. Gamon <i>et al., Chem. Mater.</i> <b>2019</b>, 9699. [3] A. Vasylenko <i>et al.,</i> <i>Nat. Commun.</i> <b>2021</b>, 5561. [4] G. Han <i>et al.,</i> <i>Science</i> <b>2024</b>, 739. [5] G. Han <i>et al.,</i> <i>Angew. Chemie. </i><b>2024</b>, in press. [6] J. Gamon <i>et al.,</i> <i>Chem. Mater.</i><b>2021</b>, 8733. [7] G. Han <i>et al.,</i> <i>J. Am. Chem. Soc.</i> <b>2021</b>, 18216. [8] B. B. Duff <i>et al.,</i> <i>Chem. Mater.</i> <b>2023</b>, 27. [9] B. B. Duff <i>et al.,</i><i>Chem.</i><i> Mater.</i> <b>2024</b>, in press.