Mapping the Various Li⁺ Jump Pathways in Li₁₀GeP₂S₁₂: From Ultraslow Exchange to High-Temperature Diffusion

The solid electrolyte Li₁₀GeP₂S₁₂ is known to exhibit exceptionally fast Li⁺ diffusion within its tetragonal crystal structure. Experimentally, however, the various Li⁺ hopping processes remain incompletely understood. In this study, we employed ⁷Li spin-alignment echo (SAE) NMR and complementary NMR techniques to resolve lithium-ion dynamics in LGPS over nearly 12 orders of magnitude in jump rates, from ultraslow local exchange at 90 K to fast long-range diffusion close to room temperature. Our data reveal a sequence of dynamic regimes and activation energies that reflect the dimensional evolution of Li⁺ transport, from localized 1D hopping to full 3D diffusion. The SAE NMR decay rates, which directly reflect slow Li⁺ jump rates, on the order of one jump every three seconds (0.32(2) s^-1) at 90 K, reveal two distinct dynamic regimes with activation energies of 0.09 and 0.18 eV, suggesting a transition from 1D to 2D diffusion. At higher temperatures, a third regime emerges, characterized by an activation energy of 0.28 eV, detected by NMR relaxation and SAE NMR. This regime likely corresponds to 3D Li⁺ transport, and the measured rates are in excellent agreement with those from pulsed field gradient NMR, quasi-elastic neutron scattering, and theoretical predictions.