Lithium-ion diffusivity in complex hydrides: Pulsed-field-gradient NMR studies of LiLa(BH4)3Cl, Li3(NH2)2I and Li-1-CB9H10

• Published in: Solid state ionics Vol. 362; p. 115585
• Main Authors: Skripov, A.V., Majer, G., Babanova, O.A., Skoryunov, R.V., Soloninin, A.V., Ley, M.B., Jensen, T.R., Orimo, S., Udovic, T.J.
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 01-04-2021
• Subjects: Complex hydrides; Diffusion; Ionic conductors; Nuclear magnetic resonance; Ionic conductors; Complex hydrides; Nuclear magnetic resonance; Diffusion
• ISSN: 0167-2738; 1872-7689
• DOI: 10.1016/j.ssi.2021.115585

The bimetallic borohydride-chloride LiLa(BH4)3Cl, the lithium amide-iodide Li3(NH2)2I, and the lithium monocarba-closo-decaborate Li-1-CB9H10 represent complex hydrides showing superionic conductivity at room temperature or slightly above it. To study the Li-ion diffusivity that is closely related to the ionic conductivity, we have measured the diffusion coefficients of Li+ cations in these compounds using the pulsed-field-gradient (PFG) spin-echo technique over the temperature range of 298–403 K. The experiments have revealed fast Li+ diffusivities in all these complex hydrides: at 400 K, the measured diffusion coefficients exceed 10−7 cm2/s for LiLa(BH4)3Cl, 5 × 10−8 cm2/s for Li3(NH2)2I, and 10−6 cm2/s for Li-1-CB9H10. For LiLa(BH4)3Cl and Li3(NH2)2I, the diffusion coefficients are found to follow the Arrhenius behavior over the entire temperature ranges studied with the activation energies of 268(6) meV and 224(6) meV, respectively. For Li-1-CB9H10, the Arrhenius behavior with the activation energy of 265(6) meV is observed in the disordered high-temperature polymorph (360–403 K), whereas below 360 K the measured diffusivity drops significantly due to the transition to the ordered phase. Comparison of the measured Li+ diffusion coefficients with the ionic conductivity results and the data on the cation and anion jump rates provides new insights into the unusual dynamical properties of these superionic materials.
•High Li+ diffusivity is revealed in three complex hydrides.•The measured activation energies for Li+ diffusion are in the range of 224–268 meV.•For LiLa(BH4)3Cl, the Li+ diffusion path includes two types of interstitial sites.•The order-disorder transition in LiCB9H10 leads to strong changes in Li+ diffusivity.•In the disordered phase of LiCB9H10, the measured diffusivity is anomalously high.