NMR and Impedance Spectroscopy Studies on Lithium Ion Diffusion in Microcrystallineγ-LiAlO₂

Abstract

Abstract:In this work nuclear magnetic resonance (NMR) and impedance spectroscopy (IS) studies on Li ion dynamics in microcrystalline -LiAlO 2 are presented. The sample was prepared by solid state synthesis between Li 2 CO 3 and Al 2 O 3 in air, followed by a quenching procedure. The presence of phase-pureLiAlO 2 was confirmed by X-ray powder diffraction including Rietveld refinement.Further structural characterization was done with 6 Li, 7 Li and 27 Al NMR. Several NMR techniques such as spin-lattice relaxation measurements, motional narrowing experiments, as well as spin-alignment echo were employed for the investigation of Li ion diffusion. The measurements were carried out at high temperatures (up to 970 K) in order to access the regime of Li ion motion being very slow. The dc conductivities measured by IS in the temperature range from 680 K to 870 K were converted to diffusion coefficients being compatible with those obtained by NMR.

Local Ion Dynamics in Polycrystalline β-LiGaO2: A Solid-State NMR Study

“…In addition, the Li + motion led to the averaging of dipolar broadening of the central transition 7 Li signal of m-LiAlO 2 . This motional narrowing ocurred in the temperature range between 500 and 900 K. The fullwidth at half-maximum (FWHM) decreased from 7 kHz to a few hundreds of Hz in this temperature range [13]. A reduction of FWHM of this order is usual for a complete motional narrowing process (involving all Li ions) leaving behind only the inhomogeneous line broadening.…”

“…Most of them focus on materials used in LIB's and investigate their dynamics, structure and conductivity behaviors. But there are only a few reports available on NMR studies of materials with purely slow Li dynamic modes alone [12][13][14]. Witt et al [13] studied the slow ionic diffusion in microcrystalline (m-) γ-lithium aluminate (LiAlO 2 ).…”

“…But there are only a few reports available on NMR studies of materials with purely slow Li dynamic modes alone [12][13][14]. Witt et al [13] studied the slow ionic diffusion in microcrystalline (m-) γ-lithium aluminate (LiAlO 2 ). From variable-temperature spinlattice relaxation (SLR) studies [15], spin-alignment echo (SAE) experiments [16] and conductivity measurements [17], a slow overall ionic diffusion with a diffusion coefficient of the order of 10 −19 m 2 s −1 at 473 K and an activation energy of 0.7 eV were found.…”

Slow Lithium Transport in Metal Oxides on the Nanoscale

“…This indicates that different Li jumps are probed. A quite recent study on microcrystalline γ-LiAlO 2 [82] with nearly the whole arsenal of NMR methods including SAE and SLR in the rotating reference frame, which are sensitive at low temperatures, as well as impedance spectroscopy consistently, yielded an activation energy of 0.7 eV.…”

Diffusion Pathways and Activation Energies in Crystalline Lithium-Ion Conductors

“…γ-LiAlO 2 (tetragonal, P4 1 2 1 2/P4 3 2 1 2; see Figure 8) is an example of an ultra-slow threedimensional lithium conductor -densely packed and lacking structural cation defects. It was investigated in different forms with a variety of techniques, such as NMR and impedance/conductivity spectroscopy on micro-to nanocrystalline [42] or amorphous powders [43], as well as on differently oriented single crystals [44][45][46]. Even dynamic mechanical analysis (DMA) has been performed [47].…”