Comparison of lithium diffusion mechanisms in complex hydrides LiLa(BH4)3Cl and Li3(NH2)2I via 7Li and 1H nuclear magnetic resonance studies
2Institut fuer Physikalische Chemie und Elektrochemie, Leibniz Universitaet Hannover, Germany
3Department of Heterogeneous Catalysis, Max-Planck-Institut fuer Kohlenforschung, Germany
4Department of Chemistry, University of Arhus, Denmark
It has been found recently that some complex hydrides of alkali metals exhibit high ionic conductivity, which suggests their potential use as solid electrolytes [1,2]. Apart from prospective practical applications, complex hydrides are of interest as model systems for studies of the mechanisms of cation diffusion. Indeed, complex anions are known to participate in a rotational (reorientational) motion, and this localized motion may affect the translational diffusion of cations [3]. In the present work, we use a combined analysis of the 7Li and 1H nuclear magnetic resonance (NMR) data over wide temperature ranges to compare the mechanisms and parameters of Li+ diffusion in the complex hydrides LiLa(BH4)3Cl and Li3(NH2)2I, both of which exhibit Li+ jump rates of the order of 108 s-1 near room temperature. For LiLa(BH4)3Cl, we have found that the diffusive Li+ jumps and a certain type of BH4– reorientations occur on the same frequency scale; this suggests that the cation diffusion and anion reorientations are correlated. In contrast, for Li3(NH2)2I, the fast Li+ diffusion is not related to the effects of NH2– reorientations; it appears to be determined by specific structural features of the Li-site sublattice.
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[3] A.V. Skripov, A.V. Soloninin, M.B. Ley, T.R. Jensen, Y. Filinchuk, J. Phys. Chem. C 117, 14965 (2013).
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