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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]

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 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]

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]

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.