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Mg(B3H8)2·2THF (THF = tetrahydrofuran) was prepared by the addition of BH3·THF to Mg/Hg amalgam. Heating a 1:2 molar mixture of Mg(B3H8)2·2THF and MgH2 to 200 °C under 5 MPa H2 for 2 h leads to nearly quantitative conversion to Mg(BH4)2. The differential scanning calorimetry profile of the reaction measured under 5 MPa H2 shows an initial endothermic feature at ~65 °C for a phase change of the compound followed by a broad exothermic feature that reaches a maximum at 130 °C corresponding to the hydrogenation of Mg(B3H8)2 to Mg(BH4)2. Heating Mg(B3H8)2·2THF to 200 °C under 5 MPa H2 pressure in the absence of MgH2 gives predominantly MgB12H12 as well as significant amounts of MgB10H10 and Mg(BH4)2. Hydrogenation of a mixture of Mg(B3H8)2·2THF and LiH in a 1:4 molar ratio at 130 °C under 5 MPa H2 yields [B12H12]2- in addition to [BH4]-, while a 1:4 molar ratio of Mg(B3H8)2·2THF and NaH yields [BH4]- and a new borane, likely [B2H7]-. Hydrogenation of the NaH-containing mixture at 130 °C gives primarily the alternative borane, indicating it is an intermediate in the two-step conversion of the triborane to [BH4]-. The solvent-free triborane Mg(B3H8)2, derived from the low-temperature dehydrogenation of Mg(BH4)2, also produces Mg(BH4)2, but higher temperature and pressure is required to effect the complete transformation of the Mg(B3H8)2. These results show that the reversible transformation of the triborane depends on the stability of the metal hydride. The more stable the metal hydride, that is, LiH > NaH > MgH2, the lower is the "regeneration" efficiency. [ABSTRACT FROM AUTHOR]

To extract a pure atomic-resolution hologram around hydrogen from a two-dimensional (2D) neutron intensity distribution around a single crystal, enhancement of the holographic signal and suppression of the diffuse scattering are important; sample cooling can achieve both. To estimate the performance of sample cooling in achieving these requirements, the angular anisotropy of the neutron intensities around a PdH078 single crystal was measured at 300 K and 100 K. In addition to the reduction in the diffuse scattering intensity, the pattern itself changed markedly upon sample cooling, thus indicating a significant modification of the hydrogen lattice dynamics. The reconstruction from a hologram, which was obtained by subtracting the diffuse scattering pattern, shows images of H and Pd nuclei as negative and positive peaks, respectively. In particular, such reconstruction at 100 K exhibits distinct H images at distant positions owing to the suppression of hydrogen motion. These features are important for the determination of hydrogen sites in various materials. [ABSTRACT FROM AUTHOR]

closo-type complex hydrides contain large cage-type complex polyanions in their crystal structures and thus can exhibit superior ion-conducting properties (e.g., Li and Na). However, the unique structures of complex polyanions have made it challenging to modify crystal structures, making systematic control of ion conductivity difficult. Here, we report an atom deficiency approach to enhance lithium-ion conductivity of complex hydrides. We find that lithium and hydrogen could be simultaneously extracted from Li2B12H12 by applying a small external energy, enabling the formation of atom deficiencies. These atom deficiencies lead to an increase in carrier concentration, improving lithium-ion conductivity by 3 orders of magnitude compared to that of a pristine material. An all-solid-state TiS2/Li battery employing atom-deficient Li2B12H12 as a solid electrolyte exhibits superior battery performance during repeated discharge-charge cycles. The current study suggests that the atom deficiency can be a useful strategy to develop high ion-conducting complex hydride solid electrolytes. [ABSTRACT FROM AUTHOR]

In previous studies, complex hydrides LiBH4 and Mg2 FeH6 have been reported to undergo simultaneous dehydrogenation when ball-milled as composite materials (1 - x)LiBH4 + xMg2 FeH6. The simultaneous hydrogen release led to a decrease of the dehydrogenation temperature by as much as 150 K when compared to that of LiBH4. It also led to the modified dehydrogenation properties of Mg2 FeH6. The simultaneous dehydrogenation behavior between stoichiometric ratios of LiBH4 and Mg2 FeH6 is not yet understood. Therefore, in the present work, we used the molar ratio x = 0.25, 0.5, and 0.75, and studied the isothermal dehydrogenation processes via pressure-composition-isothermal (PCT) measurements. The results indicated that the same stoichiometric reaction occurred in all of these composite materials, and x = 0.5 was the molar ratio between LiBH4 and Mg2 FeH6 in the reaction. Due to the optimal composition ratio, the composite material exhibited enhanced rehydrogenation and reversibility properties: the temperature and pressure of 673 K and 20 MPa of H2, respectively, for the full rehydrogenation of x = 0.5 composite, were much lower than those required for the partial rehydrogenation of LiBH4. Moreover, the x = 0.5 composite could be reversibly hydrogenated for more than four cycles without degradation of its H2 capacity. [ABSTRACT FROM AUTHOR]

In the present work, we developed highly sodium-ion conductive Na2B10H10-Na2B12H12 pseudobinary complex hydride via mechanically ball-milling admixtures of the pure Na2B10H10 and Na2B12H12 components. Both of these components show a monoclinic phase at room temperature, but ball-milled mixtures partially stabilized highly ion-conductive, disordered cubic phases, whose fraction and favored structural symmetry (body-centered cubic or face-centered cubic) depended on the conditions of mechanical ball-milling and molar ratio of the component compounds. Firstprinciples molecular-dynamics simulations demonstrated that the total energy of the closo-borane mixtures and pure materials is quite close, helping to explain the observed stabilization of the mixed compounds. The ionic conductivity of the closo-borane mixtures appeared to be correlated with the fraction of the body-centered-cubic phase, exhibiting a maximum at a molar ratio of Na2B10H10:Na2B12H12=1:3. A conductivity as high as log(σ/S cm-1)=-3.5 was observed for the above ratio at 303 K, being approximately 2-3 orders of magnitude higher than that of either pure material. A bulk-type all-solid-state sodium-ion battery with a closo-borane-mixture electrolyte, sodium-metal negative-electrode, and TiS2 positive-electrode demonstrated a high specific capacity, close to the theoretical value of NaTiS2 formation and a stable discharge/charge cycling for at least eleven cycles, with a high discharge capacity retention ratio above 91% from the second cycle. [ABSTRACT FROM AUTHOR]

On the way to transform lithium amide (LiNH2) into lithium imide (Li2NH) by releasing H2, the 1:1 molar mixture of LiNH2-LiH forms cubic (Fm3m)Fm3m) non-stoichiometric complex hydride phases (Li1+xNH2-x; 06wt.% H2 can offer high Li-ionic conductivity (>10-4 S.cm-1 at room temperature) having an electrochemical stability window >5V. The study suggests that the Li-N-H system may be a prospective electrolyte in the all-solid-state Li-ion battery, in addition to its use as a reversible hydrogen storage material. [ABSTRACT FROM AUTHOR]

Combinations of complex metal borohydrides ball milled with the transition metal complex hydride, Mg2FeH6, are analysed and compared. Initially, the Reactive Hydride Composite (RHC) of Mg2+ cation mixtures of Mg2FeH6 and γ-Mg(BH4)2 is combined in a range of molar ratios and heated to a maximum of 450 °C. For the molar ratio of 6 Mg2FeH6+Mg(BH4)2, simultaneous desorption of the two hydrides occurred, which resulted in a single event of hydrogen release. This single step desorption occurred at temperatures between those of Mg2FeH6 and γ-Mg(BH4)2. Keeping this anionic ratio constant, the desorption behavior of four other borohydrides, Li-, Na-, K-, and Ca-borohydrides was studied by using materials ball milled with Mg2FeH6 applying the same milling parameters. The mixtures containing Mg-, Li-, and Ca-borohydrides also released hydrogen in a single event. The Mass Spectrometry (MS) results show a double step reaction within a narrow temperature range for both the Na- and K-borohydride mixtures. This phenomenon, observed for the RHC systems at the same anionic ratio with all five light metal borohydride mixtures, can be described as simultaneous hydrogen desorption within a narrow temperature range centered around 300 °C. [ABSTRACT FROM AUTHOR]

In this study, we assembled a bulk-type all-solid-state battery comprised of a TiS2 positive electrode, LiBH4 electrolyte, and Li negative electrode. Our battery retained high capacity over 300 dischargeâ€"charge cycles when operated at 393 K and 0.2 C. The second discharge capacity was as high as 205 mAh gâ€"1, corresponding to a TiS2 utilization ratio of 85%. The 300th discharge capacity remained as high as 180 mAh gâ€"1 with nearly 100% Coulombic efficiency from the second cycle. Negligible impact of the exposure of LiBH4 to atmospheric-pressure oxygen on battery cycle life was also confirmed. To investigate the origin of the cycle durability for this bulk-type all-solid-state TiS2/Li battery, electrochemical measurements, thermogravimetry coupled with gas composition analysis, powder X-ray diffraction measurements, and first-principles molecular dynamics simulations were carried out. Chemical and/or electrochemical oxidation of LiBH4 occurred at the TiS2 surface at the battery operating temperature of 393 K and/or during the initial charge. During this oxidation reaction of LiBH4 with hydrogen (H2) release just beneath the TiS2 surface, a third phase, likely including Li2B12H12, precipitated at the interface between LiBH4 and TiS2. Li2B12H12 has a lithium ionic conductivity of log(σ/S cmâ€"1) = â'4.4, charge transfer reactivity with Li electrodes, and superior oxidative stability to LiBH4, and thereby can act as a stable interface that enables numerous dischargeâ€"charge cycles. Our results strongly suggest that the creation of such a stable interfacial layer is due to the propensity of forming highly stable, hydrogen-deficient polyhydro-closo-polyborates such as Li2B12H12, which are thermodynamically available in the ternary Liâ€"Bâ€"H system. [ABSTRACT FROM AUTHOR]

The dehydriding process and hydrogen-deuterium exchange (H-D exchange) of xLiBH4 + (1 - x)Mg2FeD6 (x = 0.25, 0.75) composites has been studied in detail. For the composition with x = 0.25, only one overlapping mass peak of all hydrogen and deuterium related species was observed in mass spectrometry. This implied the simultaneous dehydriding of LiBH4 and Mg2FeD6, despite an almost 190 °C difference in the dehydriding temperatures of the respective discrete complex hydrides. In situ infrared spectroscopy measurements indicated that H-D exchange between [BH4]- and [FeD6]4- had occurred during ball-milling and was promoted upon heating. The extent of H-D exchange was estimated from the areas of the relevant mass signals: immediately prior to the dehydriding, more than two H atoms in [BH4]- was replaced by D atoms. For x = 0.75, H-D exchange also occurred and about one to two H atoms in [BH4]- was replaced by D atoms immediately before the dehydriding. In contrast to the situation for x = 0.25, firstly LiBH4 and Mg2FeD6 dehydrided simultaneously with a special molar ratio = 1:1 at x = 0.75, and then the remaining LiBH4 reacted with the Mg and Fe derived from the dehydriding of Mg2FeD6. [ABSTRACT FROM AUTHOR]

Despite many exploratory studies over the past several decades, the presently known transition metals that form homoleptic transition-metal hydride complexes are limited to the Groups 7-12. Here we present evidence for the formation of Mg3CrH8, containing the first Group 6 hydride complex [CrH7]5-. Our theoretical calculations reveal that pentagonal-bipyramidal H coordination allows the formation of σ-bonds between H and Cr. The results are strongly supported by neutron diffraction and IR spectroscopic measurements. Given that the Group 3-5 elements favor ionic/ metallic bonding with H, along with the current results, the true boundary for the formation of homoleptic transition-metal hydride complexes should be between Group 5 and 6. As the H coordination number generally tends to increase with decreasing atomic number of transition metals, the revised boundary suggests high potential for further discovery of hydrogen-rich materials that are of both technological and fundamental interest. [ABSTRACT FROM AUTHOR]

Despite many exploratory studies over the past several decades, the presently known transition metals that form homoleptic transition-metal hydride complexes are limited to the Groups 7-12. Here we present evidence for the formation of Mg3CrH8, containing the first Group 6 hydride complex [CrH7]5-. Our theoretical calculations reveal that pentagonal-bipyramidal H coordination allows the formation of s-bonds between H and Cr. The results are strongly supported by neutron diffraction and IR spectroscopic measurements. Given that the Group 3-5 elements favor ionic/ metallic bonding with H, along with the current results, the true boundary for the formation of homoleptic transition-metal hydride complexes should be between Group 5 and 6. As the H coordination number generally tends to increase with decreasing atomic number of transition metals, the revised boundary suggests high potential for further discovery of hydrogen-rich materials that are of both technological and fundamental interest. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

First-principles calculations were employed to investigate hypothetical complex hydrides (M,M')4FeH8 (M = Na, Li; M' = Mg, Zn, Y, Al). Besides complex anion [FeH6]4-, these materials contain two H- anions, which raise the total anionic charge state from tetravalent to hexavalent, and thereby significantly increasing the number of combinations of countercations. We have determined that similar to complex hydrides (M,M')2FeH6 containing only [FeH6]4-, the thermodynamic stability is tuned by the average cation electronegativity. Thus, the chemical flexibility provided by incorporating H- enhances the tunability of thermodynamic stability, which will be beneficial in obtaining optimal stability for hydrogen storage materials. [ABSTRACT FROM AUTHOR]

A metallic perovskite-type hydride LiNiH3 was synthesized based on first-principles prediction. We theoretically examined its electronic structure and found that half of the Ni-H derived antibonding states are occupied and that the modest thermodynamic stability depends on a delicate balance between (i) destabilization and (ii) alleviation of compression frustration in corner-sharing octahedra, both of which arise from occupation of antibonding states. Through density-functional analyses of the electronic structure and lattice instability extending over LiTH3 series (T = Fe, Co, Ni, and Cu), we showed that the balance is in fact reflected in their thermodynamic stability. [ABSTRACT FROM AUTHOR]

Lithium hexahydridoaluminate Li3AlH6and lithium amide LiNH2with 1:2 molar ratio were mechanically milled, yielding a Li−Al−N−H system. LiNH2destabilized Li3AlH6during the dehydrogenation process of Li3AlH6, because the dehydrogenation starting temperature of the Li−Al−N−H system was lower than that of Li3AlH6. Temperature-programmed desorption scans of the Li−Al−N−H system indicated that a large amount of hydrogen (6.9 wt %) can be released between 370 and 773 K. After initial H2desorption, the H2absorption and the desorption capacities of the Li−Al−N−H system with a nano-Ni catalyst exhibited 3−4 wt % at 10−0.004 MPa and 473−573 K, while the capacities of the system without the catalyst were 1−2 wt %. The remarkably increased capacity was due to the fact that the kinetics was improved by addition of the nano-Ni catalyst. [ABSTRACT FROM AUTHOR]

Impedance measurements indicate that Na2B12H12 exhibits dramatic Na+ conductivity (on the order of 0.1 S cm-1) above its order-disorder phase-transition at ≈529 K, rivaling that of current, solid-state, ceramic-based, Na-battery electrolytes. Superionicity may be aided by the large size, quasispherical shape, and high rotational mobility of the B12H122- anions. [ABSTRACT FROM AUTHOR]

The new complex hydride Li3(NH2)2I exhibiting fast-ion conduction is reported. Li3(NH2)2I has the characteristic double-layered structure with a= 7.09109(5) Å and c= 11.50958(10) Å (P63mc). Because of the unique crystal structure, Li3(NH2)2I exhibits fast-ion conductivity of 1 × 10−5S/cm at 296 K. [ABSTRACT FROM AUTHOR]

The article features the research on the significance of complex hydrides with (BH4)- and (NH2)- as new lithium fast-ion conductors. When researchers heated these hydrides, these metals exhibited lithium fast-ion conductivity of 2 x 10-4 Siemen per centimeter (S/cm) at ~370 Kelvin (K). Moreover, they concluded that the combination of complex hydrogen anions provide new occupation site for Li+ ions.

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 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. [ABSTRACT FROM AUTHOR]