With a Little Help from (31)P NMR: The Complete Picture on Localized and Long-Range Li(+) Diffusion in Li(6)PS(5)I

[Image: see text] Li(6)PS(5)I acts as a perfect model substance to study length scale-dependent diffusion parameters in an ordered matrix. It provides Li-rich cages which offer rapid but localized Li(+) translational jump processes. As jumps between these cages are assumed to be much less frequent, long-range ion transport is sluggish, resulting in ionic conductivities in the order of 10(–6) S cm(–1) at room temperature. In contrast, the site disordered analogues Li(6)PS(5)X (X = Br, Cl) are known as fast ion conductors because structural disorder facilities intercage dynamics. As yet, the two extremely distinct jump processes in Li(6)PS(5)I have not been visualized separately. Here, we used a combination of (31)P and (7)Li NMR relaxation measurements to probe this bimodal dynamic behavior, that is, ultrafast intracage Li(+) hopping and the much slower Li(+)intercage exchange process. While the first is to be characterized by an activation energy of ca. 0.2 eV as directly measured by (7)Li NMR, the latter is best observed by (31)P NMR and follows the Arrhenius law determined by 0.44 eV. This activation energy perfectly agrees with that seen by direct current conductivity spectroscopy being sensitive to long-range ion transport for which the intercage jumps are the rate limiting step. Moreover, quantitative agreement in terms of diffusion coefficients is also observed. The solid-state diffusion coefficient D(σ) obtained from conductivity spectroscopy agrees very well with that from (31)P NMR (D(NMR) ≈ 4.6 × 10(–15) cm(2) s(–1)). D(NMR) was directly extracted from the pronounced diffusion-controlled (31)P NMR spin-lock spin–lattice relaxation peak appearing at 366 K.