Diffusion in lithium ion conductors – From fundamentals to applications

Lithium ion conductors and concomitantly the topic of Li solid state diffusion have become enormously popular in recent years. This is mainly due to the quest for better materials and performances of Li ion batteries, the leading electrochemical energy storage system. However, fundamental research on diffusion of the lightest ion besides H+, comprising questions about, e.g., the dimensionality of diffusion or the influence of structural disorder, has been intensified as well. Here, exemplary results of our group in the field of diffusion fundamentals are reviewed. Methodologically, the investigations extensively involve NMR techniques, but also impedance spectroscopy, mass spectrometry and neutron scattering are being applied

Better battery electrolytes by optimizing ion transport

The scope of Diffusion Fundamentals (DF), both as open-access journal and conference series, has greatly broadened over the past two decades. In fact, most invited lectures of the present 10th jubilee conference deal with spreading phenomena in social sciences and humanities. In the present contribution, however, I shall rather go back to the roots of diffusion of particles in matter. Diffusion and transport of Li ions, in particular, has gained enormous interest in the last decades due their use in rechargeable batteries, which are nowadays ubiquitous. Details of the Li+ jumps, e.g., jump rates, activation energies, jump mechanisms and their dimensionality, can be studied by various experimental methods. Among these, the bunch of nuclear magnetic resonance (NMR) techniques is the most versatile one. Whereas maximization of the ion conductivity of the electrolyte – preferably in the solid state for safety reasons – together with the search for an optimum electrode pair has been a continuous endeavor since the introduction of the Li ion battery in the 1990s, in recent years, the improvement of the electrolyte/electrode interfaces has received increased attention as being decisive for the optimization of battery performance

Mobility of Ions in Solids

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Lithium Ions in Solids - Between Basics and Better Batteries

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Diffusive Motion in Stage-1 and Stage-2 Li-Graphite Intercalation Compounds: Results of β-NMR and Quasielastic Neutron Scattering

Investigations of Li diffusion in stage-1 and stage-2 Li graphite intercalation compounds with neutron time-of-flight and backscattering techniques and β-radiation detected nuclear magnetic resonance/relaxation (β-NMR) with the nucleus 8Li(T1/2 = 0.8 s) are reviewed and compared. Depending on temperature, the spin-lattice relaxation-rate T1 -1of 8Li is governed by different processes. Above 300 K, T1 -1(T) shows maxima induced by long-range Li+diffusion. Jump correlation times are estimated. Inspection of the B field dependence of T1 -1revealed two-dimensional diffusion behaviour. The neutron spectra showed a quasielastic line broadening above 500 K, which was used to obtain diffusion coefficients and to trace jump vectors of the in-plane motion. The diffusion parameters observed with both techniques are compared, and differences that show up are discussed. In addition, the low-temperature spin-lattice relaxation rates, being due to coupling to conduction electrons, are used to explore electronic properties

Li jump process in h- Li0.7 Ti S2 studied by two-time Li7 spin-alignment echo NMR and comparison with results on two-dimensional diffusion from nuclear magnetic relaxation

7Li spin-alignment NMR is used to trace ultraslow diffusion of Li+ in the layered Li conductor LixTiS2 (x=0.7). Two-time correlation functions were recorded for fixed evolution times as a function of mixing time at temperatures within the 7Li rigid-lattice regime. The corresponding decay rates were identified as Li jump rates τ−1 ranging from 10−1to103s−1 between temperatures T=148 K and 213K. The jump rates obtained directly from spin-alignment echo NMR and those from diffusion induced maxima of spin-lattice relaxation peaks, monitored in the laboratory as well as in the rotating frame, are consistent with each other and follow an Arrhenius law with an activation energy of 0.41(1)eV and a preexponential factor of 6.3(1)×1012s−1. Altogether, a solitary Li diffusion process was found between 148 and 510K. Li diffusion was investigated in a dynamic range of about 10 orders of magnitude, i.e., 0.1⩽τ−1⩽7.8×108s−1. Additionally, the analysis of final-state echo amplitudes of the two-time correlation functions revealed information about the Li diffusion pathway in Li0.7TiS2. Obviously, a two-site jump process is present, i.e., besides the regularly occupied octahedral sites also the vacant tetrahedral ones within the van der Waals gap are involved in the overall two-dimensional diffusion process. © 2008 The American Physical Society