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

Longitudinal spin relaxation in simple stochastic models for disordered systems

The relaxation of single probe spins was investigated for simple models of systems with quenched disorder. The spin relaxation was calculated for a two-site model with arbitrarily oriented magnetic fields and the result was averaged over various distributions of the fields, and of the hopping rates of the spin. On an intermediate time scale, a modified Kubo-Toyabe behavior is obtained for large hopping rates, in agreement with recent SR experiments. A stretched-exponential decay of the spin polarization is obtained at longer times. The Kohlrausch exponent is found to be field and hopping-rate dependent, in qualitative agreement with recent NMR and -NMR experiments. The resulting longitudinal relaxation rate still does not show the significant deviations from the Bloembergen-Purcell-Pound (BPP) behavior that are typical for glassy systems. Therefore, the random two-frequency model was extended to include time-dependent renewals of the environment. This modification may yield asymmetric peaks for the longitudinal relaxation rate in the BPP plot for very large renewal rates. © 1995 The American Physical Society

Electric field gradient calculations for LixTiS2 and comparison with 7Li NMR results

The elements of the electric field gradient tensor at Li position in the intercalation compound LixTiS2 (with x=0.25, 0.33, 0.67, and 1.0) were calculated with first-principles methods and periodic supercell models. The theoretical results obtained with density functional and Hartree-Fock hybrid methods were compared with experimental field gradients extracted from 7Li NMR spectra from the literature and from our measurements presented here. The dependence of calculated field gradients on the basis set and the explicit form of the exchange-correlation density functional was investigated. In agreement with earlier studies a pronounced effect of polarization functions at the Li site was observed. After optimization of internal degrees of freedom in LiTiS2 all methods under consideration give quadrupole coupling constants in close agreement with experiment. For x < 1 the calculated quadrupole coupling constants were found to depend more sensitively on the method which was attributed to differences in the description of spin localization. The calculations allow one to distinguish between Li atoms placed at octahedral and tetrahedral interstitial sites of the host lattice TiS2. © 2004 American Physical Societ

Atomic-scale measurement of ultraslow Li motions in glassy LiAlSi2 O6 by two-time L6 i spin-alignment echo NMR correlation spectroscopy

6Li spin-alignment echo (SAE) nuclear-magnetic-resonance (NMR) spectroscopy is used to monitor single-particle two-time correlation functions in LiAlSi2O6 glass. The method, here applied in the temperature range from 300 to 400 K, is sensitive to ultraslow Li hopping processes with rates (1/τSAE) down to 10 jumps/s. The use of a sample with natural 6Li abundance allowed the measurement of pure NMR spin-alignment echoes which are damped with increasing mixing time exclusively by slow Li jumps, i.e., free of influences arising from, e.g., interfering spin-diffusion effects. The considerably stretched correlation functions reveal the presence of a broad distribution of jump rates. The results are comprehensively compared with those recently obtained from both 7Li SAE and 7Li spin-lattice relaxation NMR as well as from dc conductivity measurements. Interestingly, the activation energy of the latter, which are sensitive to long-range Li transport parameters, is in good agreement with that microscopically probed by 6Li SAE NMR, here. © 2008 The American Physical Society

From ultraslow to fast lithium diffusion in the 2D ion conductor Li0.7TiS2 probed directly by stimulated-echo NMR and nuclear magnetic relaxation

7Li stimulated-echo NMR and classical relaxation NMR techniques are jointly used for the first time for a comprehensive investigation of Li diffusion in layer-structured Li0.7TiS2. One single 2D Li diffusion process was probed over a dynamic range of almost 10 orders of magnitude. So far, this is the largest dynamic range being measured by 7Li NMR spectroscopy directly, i.e., without the help of a specific theoretical model. The jump rates obey a strict Arrhenius law, determined by an activation energy of 0.41(1)  eV and a preexponential factor of 6.3(1)×1012  s−1, and range between 1×10−1  s−1 and 7.8×108  s−1 (148–510 K). Ultraslow Li jumps in the kHz to sub-Hz range were measured directly by recording 7Li spin-alignment correlation functions. The temperature and, in particular, the frequency dependence of the relaxation rates fully agree with results expected for 2D diffusion. © 2006 The American Physical Society

Low-temperature DC conductivity of LiNbO 3 single crystals

We report on conductivity measurements of LiNbO3 single crystals with congruent composition in ambient atmosphere between 449 and 727 K which include the lowest temperatures covered so far. The ionic DC conductivity observed along the c-axis at, e. g., 650 K is 6.7 × 10-9 S/cm and shows an activation energy of 1.33 eV. The corresponding Li+ diffusion coefficients range between 2.5 × 10-22 and 1.4 × 10-16 m2/s. These results are perfectly consistent with our conductivity results in the high-temperature regime as well as SIMS measurements published recently (Rahn et al., Phys. Chem. Chem. Phys. 14 (2012) 2427). From the Li+ diffusion coefficients obtained here a Haven ratio of 0.7(2) can be deduced. © by Oldenbourg Wissenschaftsverlag, München

Extremely slow Li ion dynamics in monoclinic Li 2TiO 3 - Probing macroscopic jump diffusion via 7Li NMR stimulated echoes

A thorough understanding of ion dynamics in solids, which is a vital topic in modern materials and energy research, requires the investigation of diffusion properties on a preferably large dynamic range by complementary techniques. Here, a polycrystalline sample of Li 2TiO 3 was used as a model substance to study Li motion by both 7Li spin-alignment echo (SAE) nuclear magnetic resonance (NMR) and ac-conductivity measurements. Although the two methods do probe Li dynamics in quite different ways, good agreement was found so that the Li diffusion parameters, such as jump rates and the activation energy, could be precisely determined over a dynamic range of approximately eleven decades. For example, Li solid-state diffusion coefficients D σ deduced from impedance spectroscopy range from 10 -23 m 2 s -1 to 10 -12 m 2 s -1 (240-835 K). These values are in perfect agreement with the coefficients D SAE deduced from SAE NMR spectroscopy. As an example, D SAE = 2 × 10 -17 m 2 s -1 at 433 K and the corresponding activation energy determined by NMR amounts to 0.77(2) eV (400-600 K). At room temperature D σ takes a value of 3 × 10 -21 m 2 s -1. This journal is © 2012 the Owner Societies

Nanocrystalline versus microcrystalline Lo2O:B2O 3 composites: Anomalous ionic conductivities and percolation theory

We study ionic transport in nano- and microcrystalline (1−x)Li2O:xB2O3 composites using standard impedance spectroscopy. In the nanocrystalline samples (average grain size of about 20 nm), the ionic conductivity σdc increases with increasing content x of B2O3 up to a maximum at x≈0.5. Above x≈0.92, σdc vanishes. By contrast, in the microcrystalline samples (grain size about 10μm), σdc decreases monotonically with x and vanishes above x≈0.55. We can explain this strikingly different behavior by a percolation model that assumes an enhanced conductivity at the interfaces between insulating and conducting phases in both materials and explicitly takes into account the different grain sizes. © 2000 The American Physical Society

Symmetry reduction due to gallium substitution in the garnet Li6.43(2)Ga0.52(3)La2.67(4)Zr2O12

Single-crystal structure refinements on lithium lanthanum zirconate (LLZO; Li7La3Zr2O12) substituted with gallium were successfully carried out in the cubic symmetry space group I [Formula: see text]3d. Gallium was found on two lithium sites as well as on the lanthanum position. Due to the structural distortion of the resulting Li6.43(2)Ga0.52(3)La2.67(4)Zr2O12 (Ga-LLZO) single crystals, a reduction of the LLZO cubic garnet symmetry from Ia[Formula: see text] d to I [Formula: see text]3d was necessary, which could hardly be analysed from X-ray powder diffraction data.DFG/TMG/GE1981/31DFG/TMG/GE1981/32Niedersächsisches Ministerium für Wissenschaft und Kultur (MWK)/PH/74ZN99