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.
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.

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