⁷Li NMR Studies of Short-Range and Long-Range Lithium Ion Dynamics in a Heat-Treated Lithium Iodide-Doped Lithium Thiophosphate Glass Featuring High Ion Conductivity

Abstract

We combine 7 Li field-cycling relaxometry with 7 Li field-gradient diffusometry to study both short-range and long-range lithium ion dynamics in a heat-treated 0.33 LiI + 0.67 Li 3 PS 4 glass, which exhibits a high ionic conductivity of 6.5 mS/cm. 7 Li field-cycling relaxometry, which provides access to the spin−lattice relaxation time T 1 over broad frequency and temperature ranges, allows us to determine the activation energy distribution g(E a ) of the local jumps in a model-free way. We find that g(E a ) has a Gaussian form and is characterized by the mean energy E m = 0.40 eV and the standard deviation σ = 0.08 eV. 7 Li field-gradient studies indicate free diffusion and yield self-diffusion coefficients of D ∼ 10 −12 m 2 /s at ambient temperatures. Comparing our results for the short-range and long-range ion dynamics and considering previous knowledge about ionic conductivity, we show that the local jumps characterized by the Gaussian distribution g(E a ) determine the macroscopic transport. We conclude that the high ionic conductivity of the heat-treated glass does not result from the formation of minor crystalline regions during the annealing process but rather from a modification of the predominant amorphous phase.

Heat Treatment-Induced Conductivity Enhancement in Sulfide-Based Solid Electrolytes: What is the Role of the Thio-LISICON II Phase and of Other Nanoscale Phases?

“…An alternative explanation for the conductivity enhancement was suggested by Spannenberger et al, namely, a heat treatment-induced faster ion transport in the amorphous phase. 21,22 In this paper, we present the results of a comprehensive study on the thiophosphate-based electrolyte system (1 − x) Li 3 PS 4 + x LiI with x = 0−0.5. After ball milling, the electrolytes already exhibit a relatively high ionic conductivity in the amorphous state, so that even higher conductivities are expected after heat treatment.…”

“…Therefore, the crystal structure of the thio-LISICON II phase has never been clarified until now. An alternative explanation for the conductivity enhancement was suggested by Spannenberger et al, namely, a heat treatment-induced faster ion transport in the amorphous phase. , …”

Dynamical Susceptibilities of Confined Water from Room Temperature to the Glass Transition

“…The fact that, in this high-temperature range, the BDS and NMR studies yield somewhat different HN shape parameters may result from a different relevance of cross correlations in these experiments. , Thus, a nearly symmetric (CC-like) low-temperature shape evolves into a strongly asymmetric (CD-like) high-temperature one. Alternatively, we rescale the BDS data according to predictions for thermally activated motion governed by a temperature-independent and very broad distribution of energy barriers, , which is typical of β relaxations at T < T g . The rescaling aims at removing the characteristic peak broadening occurring in such situation upon cooling.…”

Unlocking Li superionic conductivity in face-centred cubic oxides via face-sharing configurations

“…These values are much smaller than the apparent activation energy determined from EIS (that is, 255 meV) because EIS measures the overall macroscopic Li-ion conductivity that includes the contributions from temperature-dependent correlated motion, grain boundaries and pores, whereas NMR probes the rate of local ion hopping 26 . The NMR-probed Li-hopping barriers of o-LISO are much smaller than those of other SICs reported in the literature [27][28][29] , suggesting a very high intrinsic Li mobility in the structure.…”