Combining 7Li NMR field-cycling relaxometry and stimulated-echo experiments: A powerful approach to lithium ion dynamics in solid-state electrolytes

Abstract

We use 7Li NMR to study lithium ion dynamics in a (Li2S)–(P2S5) glass. In particular, it is shown that a combination of 7Li field-cycling relaxometry and 7Li stimulated-echo experiments allows us to cover a time window extending over 10 orders of magnitude without any gaps. While the 7Li stimulated-echo method proved suitable to measure correlation functions F2(t) of lithium ion dynamics in solids in recent years, we establish the 7Li field-cycling technique as a versatile tool to ascertain the spectral density J2(ω) of the lithium ionic motion in this contribution. It is found that the dynamic range of 7Li field-cycling relaxometry is 10−9–10−5s and, hence, it complements in an ideal way that of 7Li stimulated-echo experiments, which amounts to 10−5–101s. Transformations between time and frequency domains reveal that the field-cycling and stimulated-echo approaches yield results for the translational motion of the lithium ions that are consistent both with each other and with findings for the motional narrowing of 7Li NMR spectra of the studied (Li2S)–(P2S5) glass. In the 7Li field-cycling studies of the (Li2S)–(P2S5) glass, we observe the translational ionic motion at higher temperatures and the nearly constant loss at lower temperatures. For the former motion, the frequency dependence of the measured spectral density is well described by a Cole–Davidson function. For the latter phenomenon, which was considered as an universal phenomenon of disordered solids in the literature, we find an exponential temperature dependence.