[en] Phonon contribution to thermal conductivity of ZrH_1.6 is studied by nonequilibrium molecular dynamics (NEMD) method. Calculated thermal conductivities were compared with the values estimated from experiment results. The difference between simulated and experimental values is acceptable, considering no adjustment on potential function used in NEMD and uncertainty in estimation of the experimental value by Wiedemann-Franz relationship. The analysis of vibrational modes has been done by equilibrium molecular dynamics (EMD) method. It was pointed out that the high frequency vibration mode of hydrogen is important for heat conduction in ZrH_1.6

[en] In order to clarify the effect of hydrogen vacancies on the stability and structure of sodium alanate, NaAlH₄, with and without Ti substitution for Al, first-principles electronic structure calculations were carried out. The relative thermodynamic stability of the Ti dopant and the H vacancy in a supercell was obtained. For the Ti-doped Na₁₆Al₁₆H₆₄ supercell calculations, it was preferable to perform the initial substitution with a cluster of TiAlH_n. We showed that substitution of a Ti atom for an Al atom in Na₁₆Al₁₅TiH₆₃ with H vacancies increases the stability of the structure. A density of states analysis revealed weakening of the bond strength corresponding to increase in the bond length.

[en] The ionic conduction and electrochemical and thermal stabilities of the LiBH₄–LiCl solid-state electrolyte were investigated for use in bulk-type all-solid-state lithium-sulfur batteries. The LiBH₄–LiCl solid-state electrolyte exhibiting a lithium ionic conductivity of $\mathrm{l}\mathrm{o}\mathrm{g}\left(\mathrm{\sigma <!--\; ??\; -->}/\mathrm{S}\mathrm{c}{\mathrm{m}}^{-<!--\; ???\; -->1}\right)=-<!--\; ???\; -->3.3$ at 373 K, forms a reversible interface with a lithium metal electrode and has a wide electrochemical potential window up to 5 V. By means of the high-energy mechanical ball-milling technique, we prepared a composite powder consisting of elemental sulfur and mixed conductive additive, i.e., Ketjen black and Maxsorb. In that composite powder, homogeneous dispersion of the materials is achieved on a nanometer scale, and thereby a high concentration of the interface among them is induced. Such nanometer-scale dispersals of both elemental sulfur and carbon materials play an important role in enhancing the electrochemical reaction of elemental sulfur. The highly deformable LiBH₄–LiCl electrolyte assists in the formation of a high concentration of tight interfaces with the sulfur-carbon composite powder. The LiBH₄–LiCl electrolyte also allows the formation of the interface between the positive electrode and the electrolyte layers, and thus the Li-ion transport paths are established at that interface. As a result, our battery exhibits high discharge capacities of 1377, 856, and 636 mAh g^–1 for the 1st, 2nd, and 5th discharges, respectively, at 373 K. These results imply that complex hydride-based solid-state electrolytes that contain Cl-ions in the crystal would be integrated into rechargeable batteries. (paper)

[en] Highlights: ► A possible synthesis of Y₂CrH₆ was theoretically investigated. ► We found the thermodynamically stable structure with a hexavalent [CrH₆]⁶⁻. ► The large charge state of [CrH₆]⁶⁻ brings diversity to the cation combinations. ► The large charge state would provide a chemical flexibility to the complex hydride. -- Abstract: The crystal, electronic and phonon structures, and thermodynamic stability of a hypothetical complex hydride Y₂CrH₆ were investigated using first-principles calculations. We found that the hydride contains CrH₆ octahedra in the K₂PtCl₆-type structure. The electronic structure illustrates that two yttrium atoms donate a total of six electrons to the octahedra, indicating the charge state Y₂³⁺[CrH₆]^6- which abides by the 18-electron rule. The phonon dispersion curves demonstrate that the hydride is dynamically stable. The calculated enthalpy change of −11 kJ/mol for the reaction, 2YH₂+Cr + H₂ → Y₂CrH₆, gives a possible route to synthesize the stable complex hydride containing [CrH₆]⁶⁻. The large charge state of the hexavalent complex anion [CrH₆]⁶⁻ would be useful to explore new complex hydrides, providing the chemical flexibility through the multiple combinations of cations

[en] We report on the synthesis of lithium hydride (LiH) epitaxial thin films through the hydrogenation of a Li melt, forming abrupt LiH/MgO interface. Experimental and first-principles molecular dynamics studies reveal a comprehensive microscopic picture of the crystallization processes, which sheds light on the fundamental atomistic growth processes that have remained unknown in the vapor-liquid-solid method. We found that the periodic structure that formed, because of the liquid-Li atoms at the film/MgO-substrate interface, serves as an atomic template for the epitaxial growth of LiH crystals. In contrast, films grown on the Al₂O₃ substrates indicated polycrystalline films with a LiAlO₂ secondary phase. These results and the proposed growth process provide insights into the preparation of other alkaline metal hydride thin films on oxides. Further, our investigations open the way to explore fundamental physics and chemistry of metal hydrides including possible phenomena that emerge at the heterointerfaces of metal hydrides

[en] Stable battery operation of a bulk-type all-solid-state lithium-sulfur battery was demonstrated by using a LiBH₄ electrolyte. The electrochemical activity of insulating elemental sulfur as the positive electrode was enhanced by the mutual dispersion of elemental sulfur and carbon in the composite powders. Subsequently, a tight interface between the sulfur-carbon composite and the LiBH₄ powders was manifested only by cold-pressing owing to the highly deformable nature of the LiBH₄ electrolyte. The high reducing ability of LiBH₄ allows using the use of a Li negative electrode that enhances the energy density. The results demonstrate the interface modification of insulating sulfur and the architecture of an all-solid-state Li-S battery configuration with high energy density.

[en] We use first-principles molecular dynamics to study the electrochemical solid-solid interface between lithium metal and lithium electrolyte LiBH₄. An external bias is applied by using an effective screening medium. We observe large polarization in the LiBH₄, because the lithium cations in LiBH₄ are shifted more on one side of the double-well potential of Li⁺. This results in a large potential drop in the interface region and a large double-layer capacity corresponding to ca. 70 μF/cm². H-coordination to the Li atoms plays an important role in the charge-transfer reaction and ion transfer