Lithium ion dynamics in Li2S+GeS2+GeO2 glasses studied using 7Li NMR field-cycling relaxometry and line-shape analysis

Abstract

We use (7)Li NMR to study the ionic jump motion in ternary 0.5Li2S+0.5[(1-x)GeS2+xGeO2] glassy lithium ion conductors. Exploring the "mixed glass former effect" in this system led to the assumption of a homogeneous and random variation of diffusion barriers in this system. We exploit that combining traditional line-shape analysis with novel field-cycling relaxometry, it is possible to measure the spectral density of the ionic jump motion in broad frequency and temperature ranges and, thus, to determine the distribution of activation energies. Two models are employed to parameterize the (7)Li NMR data, namely, the multi-exponential autocorrelation function model and the power-law waiting times model. Careful evaluation of both of these models indicates a broadly inhomogeneous energy landscape for both the single (x=0.0) and the mixed (x=0.1) network former glasses. The multi-exponential autocorrelation function model can be well described by a Gaussian distribution of activation barriers. Applicability of the methods used and their sensitivity to microscopic details of ionic motion are discussed.

From Local to Diffusive Dynamics in Polymer Electrolytes: NMR Studies on Coupling of Polymer and Ion Dynamics across Length and Time Scales

“…The detection fields amounted to 42 and 28 MHz in the former and latter cases, respectively. The temperature was controlled with a flow cryostat for gaseous nitrogen and stabilized on ±0.2 K with a total accuracy of 1 K. Further experimental details of our 1 H and 7 Li FC approaches can be found in previous works. ,− …”

NMR Investigations of Crystalline and Glassy Solid Electrolytes for Lithium Batteries: A Brief Review

“…While MAS is extremely useful at determining the local structure of glassy materials, alternate methods such as relaxometry can probe the Li ion dynamics at various timescales [14]. Marple et al studied the Li-ion dynamics of Chalcogenide Glasses, composed of Li2S, Ga2Se3, and GeSe2 (LGGS) in mixed compositions, ranging from 7.5% to 50% Li [15,16].They performed electrochemical impedance spectroscopy (EIS) to find ionic conductivities as a function of both composition and temperature, and extracted Li ion activation energies from the subsequent Arrhenius plots.…”

“…It is known that combinations of glass formers can lead to anomalously ionic conductivities, hereafter referred to as the "mixed glass former effect" (MGFE) [12,14,[18][19][20]. This effect can either drastically increase or decrease ionic conductivity, known as the positive and negative MGFE, Plotting the 7 Li NMR lineshapes for each glass reveals a characteristic sigmoid shape.…”

Relation of short-range and long-range lithium ion dynamics in glass-ceramics: Insights fromLi7NMR field-cycling and field-gradient studies

“…In particular, 7 Li spin-lattice relaxation (SLR) analysis has a long-standing tradition in studies of local lithium ion dynamics in solid electrolytes. [13][14][15][16] While traditional approaches used a single or, occasionally, a few magnetic fields B 0 and, thus, Larmor frequencies ω L , recent studies showed that 7 Li field cycling (FC) enables measurements of the SLR time T 1 in a broad continuous range of ω L values, 17,18 providing straightforward access to the frequency-dependent spectral density of the lithium ion jump motion. In addition to these studies of lithium ion dynamics on local scales in homogeneous magnetic fields, 7 Li NMR experiments in magnetic field gradients allow one to observe lithium ion diffusion on mesoscopic scales on the order of 1 µm, in particular, to measure the selfdiffusion coefficient D.…”

“…Motivated by previous FC work, 26 including our 7 Li FC studies, 17,18 we exploit the fluctuation-dissipation relation between the imaginary parts of dynamic susceptibilities and the spectral densities, χ ′′ (ω) = ωJ(ω), and present the results in the form of a generalized 'NMR susceptibiliy' defined as χ…”