I11-High Resolution Powder Diffraction
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Diamond Proposal Number(s):
[29197]
Open Access
Abstract: An increased electrification of society calls for a revolution of battery technologies to further improve energy densities, safety and reduce dependencies on critical raw materials. Here we present a new type of fast magnesium electrolytes for all solid-state batteries created as solid solutions of two other fast Mg2+ ionic conductors, Mg(BH4)2 ∙ NH3 and Mg(BH4)2 ∙ CH3NH2. However, the different ligands introduce stacking faults in the structures of the solid solutions, which are eliminated upon heating to T > 40 °C. The stacking faults appear to influence ionic conductivity, as the samples are less conductive after heating. Interestingly, the ionic conductivity does not correlate directly with the relative ligand content, as the highest conductivity is observed for the 1:1 molar composition (σ(Mg2+) = 7.3 ∙ 10−6 S cm−1 at 40 °C), which also has the lowest melting point of 60 °C. Thus, this work demonstrates a new approach to increase cationic conductivity using mixed ligand systems to alter conduction pathways and introduce microstructural strain.
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Jun 2024
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I11-High Resolution Powder Diffraction
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Open Access
Abstract: Magnesium solid-state batteries attract significant attention as a future mean of energy storage. Here we present the first cathode study of an inorganic all-solid-state magnesium battery using a magnesium metal anode, a nanocomposite electrolyte Mg(BH4)2·1.6NH3-MgO(75 wt%), and a layered titanium disulfide (TiS2) as cathode active material. The structural transformations of TiS2 particles with different size are investigated at different stages of battery life. Reversible Mg2+ intercalation occurs via three structurally distinct phases of MgxTiS2, identified by powder X-ray diffraction. Magnesium intercalates initially on octahedral sites and at higher depth of discharge on tetrahedral sites in the interlayers of TiS2, which leads to an expansion initially mainly along the c-axis and later along both the a- and c-axes. A maximum discharge capacity of 172 mAh g-1 (Δx = 0.36 in MgxTiS2) is observed for smaller TiS2 particles. Parasitic reactions could be reduced by decreasing the cut-off voltage by a constant current constant voltage cycling procedure. The chemical diffusion coefficient of the entire cell is found from galvanostatic intermittent titration technique experiments to be in the order of 10-15 to 10-19 cm2 s-1.
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Jun 2023
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I11-High Resolution Powder Diffraction
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Abstract: Solid-state magnesium electrolytes may pave the way for novel types of rechargeable, sustainable, and cheap batteries with high volumetric and gravimetric capacities. There are, however, currently no solid-state magnesium electrolytes that fulfill the requirements for solid-state battery applications. Here, we present the synthesis, structure, and properties of six new methylamine magnesium borohydride compounds, α- and β-Mg(BH4)2·6CH3NH2, Mg(BH4)2·3CH3NH2, and α-, α′- and β-Mg(BH4)2·CH3NH2. The β-Mg(BH4)2·CH3NH2 polymorph displays a record high Mg2+ ionic conductivity of σ(Mg2+) = 1.50 × 10–4 S cm–1 at room temperature. The high Mg2+ conductivity of β-Mg(BH4)·CH3NH2 is facilitated by a one-dimensional chain-like structure interconnected by weak dihydrogen bonds and dispersion interactions, forming a migration pathway across the chains. The oxidative stability of Mg(BH4)2·CH3NH2 is ∼1.2 V vs Mg/Mg2+, and the reversible plating and stripping were confirmed by cyclic voltammetry and symmetric cell cycling, revealing high stability toward magnesium electrodes for at least 50 cycles at 60 °C.
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Jan 2023
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I11-High Resolution Powder Diffraction
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Abstract: Ammonium borohydride, NH4BH4, has the highest gravimetric and volumetric hydrogen density among known inorganic compounds and a fascinating rock salt type crystal structure composed of H disordered tetrahedral complexes, NH4+ and BH4−, which are interlinked by a dense network of dihydrogen bonds. Here we report the synthesis, structure and properties of solid solutions in the binary systems, NH4BH4–MBH4 (M = K, Rb, Cs), which are investigated by in situ synchrotron radiation powder X-ray diffraction and thermal and photographic analysis. Full solubility and formation of (NH4)xM1−xBH4, is observed upon cryo-mechanochemical treatment. The solid solutions stabilize NH4BH4 from T ∼68 to ∼96 °C, alter the decomposition pathway and suppress the fierce decomposition of NH4BH4. However, for increased amounts of NH4BH4 in the solid solutions, the decomposition gradually shows more resemblance to that of pristine ammonium borohydride, and the thermal stability of the solid solutions appears to decrease down the group of the alkali metal ions, i.e. decreasing from K+, Rb+ and to Cs+.
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Nov 2022
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I11-High Resolution Powder Diffraction
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Diamond Proposal Number(s):
[29197]
Abstract: Metal closo-boranes have recently received significant attention as solid-state electrolytes due to their high thermal and electrochemical stability, and the weak interaction between the cat- and anion, facilitating fast ionic conductivity. Here we report a synthesis method for obtaining a novel mixed closo-carborane compound, [NH(CH3)3][(CB8H9)0.26(CB9H10)0.66(CB11H12)0.08]. The crystal structures are investigated for [NH(CH3)3][CB9H10] and [NH(CH3)3][(CB8H9)0.26(CB9H10)0.66(CB11H12)0.08], revealing that the latter forms a solid solution isostructural to [NH(CH3)3][CB9H10]. The compounds exhibit polymorphism as a function of temperature, and we report the discovery of four polymorphs of [NH(CH3)3][CB9H10] and four isostructural solid solution [NH(CH3)3][(CB8H9)0.26(CB9H10)0.66(CB11H12)0.08], along with a high-temperature decomposition intermediate of the latter. The α-polymorph is an ordered structure, with increasing amounts of disorder for the β- and γ-polymorphs, while the high temperature δ- and ε-polymorphs at T > 476 K are fully disordered on both the cation and anion site. These new compounds may be used as precursors for new types of solid-state ionic conductors.
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Sep 2022
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I11-High Resolution Powder Diffraction
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Abstract: Metal closo-borates are attractive electrolytes for solid state batteries. Here we present a detailed investigation of the polymorphism and thermal and electrochemical properties of Li2B10H10 and Li2B12H12 and their composites, (1 − x)Li2B12H12–xLi2B10H10. A new polymorph, β-Li2B10H10, is identified with a cubic structure, a = 9.567(1) Å (Fm[3 with combining macron]m), with dynamically disordered B10H102− anions. A sub-stoichiometric compound denoted as γ-Li2B10H10−y is prepared by thermal treatment (380 °C, 1 hour) in hydrogen and can be indexed to a cubic face-centered unit cell with a = 9.9224(5) Å. The 7Li MAS NMR spectra along with spin–lattice relaxation (T1) measured by 7Li saturation-recovery NMR experiments clearly reveal a high degree of dynamics assigned to increasing amounts of γ-Li2B10H10−y, which is in accordance with the measured Li+ ionic conductivity. Thermal treatment (380 °C, 1 hour) of Li2B12H12 in argon reveals the highest degree of dynamics and Li+ conductivity. The (1 − x)Li2B12H12–xLi2B10H10 composites are found to be physical mixtures of γ-Li2B10H10−y and Li2B12H12 with minor amounts of α-Li2B10H10, and their Li+ conductivities are proportional to the amount of γ-Li2B10H10−y. The highest Li+ conductivity is observed for γ-Li2B10H10−y: σ(Li+) = 7.6 × 10−6 S cm−1 at 30 °C and 7.2 × 10−3 S cm−1 at T = 330 °C. Cyclic voltammetry of γ-Li2B10H10−y reveals an oxidative stability up to 2.8 V vs. Li/Li+, and a stable plating and stripping of lithium.
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Jul 2022
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I11-High Resolution Powder Diffraction
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Diamond Proposal Number(s):
[26090]
Open Access
Abstract: Solid-state inorganic magnesium batteries are considered as potential high energy storage devices for the future. Here we present a series of magnesium borohydride tetrahydrofuran (THF) composites, Mg(BH 4 ) 2 · x THF(−MgO), 0 ≤ x ≤ 3, as solid-state electrolytes for magnesium batteries. Three new monoclinic compounds were identified, Mg(BH 4 ) 2 ·2/3THF ( Cc ), α-Mg(BH 4 ) 2 ·2THF ( P2 1 /c ) and β-Mg(BH 4 ) 2 ·2THF ( C2 ), and the detailed structures of α− and β−Mg(BH 4 ) 2 ·2THF are presented. The magnesium ionic conductivity of composites formed by these compounds were several orders of magnitude higher than that of the distinct compounds, x = 0, 2/3, 2, and 3. The nanocomposite stabilized by MgO nanoparticles (~50 nm), Mg(BH 4 ) 2 ·1.5THF−MgO(75 wt%), displayed the highest Mg 2+ conductivity, σ(Mg 2+ ) ~10 -4 S cm -1 at 70 °C, a high ionic transport number of t ion = 0.99, and cyclic voltammetry revealed an oxidative stability of ~1.2 V vs. Mg/Mg 2+ . The electrolyte was stable towards magnesium electrodes, which allowed for stable Mg plating/stripping for at least 100 cycles at 55 °C with a current density of 0.1 mA cm -2 . Finally, a proof-of-concept rechargeable solid-state magnesium battery was assembled with a magnesium metal anode, a TiS 2 cathode providing a maximum discharge capacity of 94.2 mAh g -1 , which corresponds to y = 0.2 in Mg y TiS 2.
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Jun 2022
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I11-High Resolution Powder Diffraction
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Diamond Proposal Number(s):
[17433]
Open Access
Abstract: Fast Li-ion conductivity at room temperature is a major challenge for utilization of all-solid-state Li batteries. Metal borohydrides with neutral ligands are a new emerging class of solid-state ionic conductors, and here we report the discovery of a new mono-methylamine lithium borohydride with very fast Li + conductivity at room temperature. LiBH 4 ∙CH 3 NH 2 crystallizes in the monoclinic space group P 2 1 / c , forming a two-dimensional unique layered structure. The layers are separated by hydrophobic –CH 3 moieties, and contain large voids, allowing for fast Li-ionic conduction in the interlayers, σ(Li+) = 1.24∙10 -3 S/cm at room temperature. The electronic conductivity is negligible, and the electrochemical stability is ~2.1 V vs Li. The first all-solid-state battery using a lithium borohydride with a neutral ligand as the electrolyte, Li-metal as the anode and TiS 2 as the cathode is demonstrated.
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Jun 2022
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I11-High Resolution Powder Diffraction
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Diamond Proposal Number(s):
[21804]
Abstract: Complex metal hydrides are a fascinating and continuously expanding class of materials with many properties relevant for solid-state hydrogen and ammonia storage and solid-state electrolytes. The crystal structures are often investigated using powder X-ray diffraction (PXD), which can be ambiguous. Here, we revisit the crystal structure of Y(11BD4)3·3ND3 with the use of neutron diffraction, which, in comparison to previous PXD studies, provides accurate information about the D positions in the compound. Upon cooling to 10 K, the compound underwent a polymorphic transition, and a new monoclinic low-temperature polymorph denoted as α-Y(11BD4)3·3ND3 was discovered. Furthermore, the series of Y(11BH4)3·xNH3 (x = 0, 3, and 7) were also investigated with inelastic neutron scattering and infrared spectroscopy techniques, which provided information of the local coordination environment of the 11BH4– and NH3 groups and unique insights into the hydrogen dynamics. Partial deuteration using ND3 in Y(11BH4)3·xND3 (x = 3 and 7) allowed for an unambiguous assignment of the vibrational bands corresponding to the NH3 and 11BH4– in Y(11BH4)3·xNH3, due to the much larger neutron scattering cross section of H compared to D. The vibrational spectra of Y(11BH4)3·xNH3 could roughly be divided into three regions: (i) below 55 meV, containing mainly 11BH4– librational motions, (ii) 55–130 meV, containing mainly NH3 librational motions, and (iii) above 130 meV, containing 11B–H and N–H bending and stretching motions.
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Jul 2021
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I11-High Resolution Powder Diffraction
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Open Access
Abstract: The structure and reorientational dynamics of KB3H8 were studied by using quasielastic and inelastic neutron scattering, Raman spectroscopy, first-principles calculations, differential scanning calorimetry, and in situ synchrotron radiation powder X-ray diffraction. The results reveal the existence of a previously unknown polymorph in between the α′- and β-polymorphs. Furthermore, it was found that the [B3H8]− anion undergoes different reorientational motions in the three polymorphs α, α′, and β. In α-KB3H8, the [B3H8]− anion performs 3-fold rotations in the plane created by the three boron atoms, which changes to a 2-fold rotation around the C2 symmetry axis of the [B3H8]− anion upon transitioning to α′-KB3H8. After transitioning to β-KB3H8, the [B3H8]− anion performs 4-fold rotations in the plane created by the three boron atoms, which indicates that the local structure of β-KB3H8 deviates from the global cubic NaCl-type structure. The results also indicate that the high reorientational mobility of the [B3H8]− anion facilitates the K+ cation conductivity, since the 2-orders-of-magnitude increase in the anion reorientational mobility observed between 297 and 311 K coincides with a large increase in K+ conductivity.
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Feb 2021
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