A quasielastic and inelastic neutron scattering study of the alkaline and alkaline-earth borohydrides LiBH4 and Mg(BH4)2 and the mixture LiBH4 + Mg(BH4)2

Silvi, Luca; Zhao‐Karger, Zhirong; Röhm, Eva; Fichtner, Maximilian; Petry, W.; Lohstroh, Wiebke

doi:10.1039/c8cp04316g

Cited by 18 publications

(9 citation statements)

References 50 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…In Fig. A8a, the dissipative part of the dynamical susceptibility of as-received γ-Mg(BH 4 ) 2 at 310 K is compared to the one of α-Mg(BH 4 ) 2 at 300 K 30 , illustrating that the external modes in γ-Mg(BH 4 ) 2 are even softer, but clearly as rich or even richer in features as α-Mg(BH 4 ) 2 . The plot highlights the dependency of the excitations on the long range structure of the respective Mg(BH 4 ) 2 polymorph.…”

Section: Resultsmentioning

confidence: 99%

Dynamics of porous and amorphous magnesium borohydride to understand solid state Mg-ion-conductors

Heere

Hansen

Payandeh

et al. 2020

Sci Rep

Self Cite

View full text Add to dashboard Cite

Rechargeable solid-state magnesium batteries are considered for high energy density storage and usage in mobile applications as well as to store energy from intermittent energy sources, triggering intense research for suitable electrode and electrolyte materials. Recently, magnesium borohydride, Mg(BH 4) 2 , was found to be an effective precursor for solid-state Mg-ion conductors. During the mechanochemical synthesis of these Mg-ion conductors, amorphous Mg(BH 4) 2 is typically formed and it was postulated that this amorphous phase promotes the conductivity. Here, electrochemical impedance spectroscopy of as-received γ-Mg(BH 4) 2 and ball milled, amorphous Mg(BH 4) 2 confirmed that the conductivity of the latter is ~2 orders of magnitude higher than in as-received γ-Mg(BH 4) 2 at 353 K. Pair distribution function (PDF) analysis of the local structure shows striking similarities up to a length scale of 5.1 Å, suggesting similar conduction pathways in both the crystalline and amorphous sample. Up to 12.27 Å the PDF indicates that a 3D net of interpenetrating channels might still be present in the amorphous phase although less ordered compared to the as-received γ-phase. However, quasi elastic neutron scattering experiments (QenS) were used to study the rotational mobility of the [BH 4 ] units, revealing a much larger fraction of activated [BH 4 ] rotations in amorphous Mg(BH 4) 2. These findings suggest that the conduction process in amorphous Mg(BH 4) 2 is supported by stronger rotational mobility, which is proposed to be the so-called "paddle-wheel" mechanism. Energy storage is one of the grand challenges for present and future generations. In recent years, intermittent renewable energy production has increased worldwide resulting in a high demand for energy storage systems. "Beyond Li-batteries", which are all-solid-state batteries with alternative working ions, including Na and Mg, are considered a promising alternative as they are cheaper and with respect to their natural abundancy more sustainable. However, the transport properties of larger Na + or double-charged Mg 2+ are challenging and directly correlated to the underlying crystal structure and dynamics. Understanding the accompanying structural and dynamic changes as well as finding high-performance cathode materials remain bottlenecks for the improvement of Mg-ion batteries 1. Mg-ion batteries (MIBs) have several advantages compared to Li-ion technology 2. For instance, the low electrochemical potential of −2.4 V (vs. standard hydrogen electrode (SHE)) is close to the one of Li with −3.0 V of Li/Li + , which allows for high cell voltages. Furthermore, Mg metal has a higher volumetric capacity of 3833 mA•cm −3 compared to 2036 mAh•cm −3 of Li metal, and magnesium has a higher natural abundancy of

show abstract

Section: Resultsmentioning

confidence: 99%

Dynamics of porous and amorphous magnesium borohydride to understand solid state Mg-ion-conductors

Heere

Hansen

Payandeh

et al. 2020

Sci Rep

Self Cite

View full text Add to dashboard Cite

show abstract

“…Moreover, QENS can give quantitative insight into atomic-scale proton 138 and ionic conduction mechanisms in ionic liquids or solid electrolytes [139][140][141] . These instruments also have a role in the optimization of the thermodynamic stability, kinetics and reversibility of hydrogen storage in solid-state materials 142 and the dynamics of ions and molecules in green energy materials such as polymer-based batteries 143 .…”

Section: [H1] Conclusion and Outlookmentioning

confidence: 99%

High-resolution neutron spectroscopy using backscattering and neutron spin-echo spectrometers in soft and hard condensed matter

et al. 2020

View full text Add to dashboard Cite

show abstract

“…It appears that at 297 K less

{({BH}_{4})}^{-}

tetrahedra are moving than at above 347 K. This hindrance also extends to higher temperatures. With p , the fraction of hindered

{({BH}_{4})}^{-}

tetrahedra,

{EISF}_{p}

and

{QISF}_{p}

, are defined [ 52,54,55 ]

\begin{array}{l} left & {EISF}_{p} = p + false(1 - p false) A_{C_{2} false/ C_{3}} \\ left & {QISF}_{p} = 1 - p - false(1 - p false) A_{C_{2} false/ C_{3}} = 1 - {EISF}_{p} \end{array}

…”

Section: Resultsmentioning

confidence: 99%

“…In the low‐temperature orthorhombic structure, the

{({BH}_{4})}^{-}

tetrahedra show a jump rotation around the

C_{3}

axis. [ 50–52 ] Detailed QENS analysis of the hexagonal phase revealed an orbit exchange reorientation model with three hydrogen atoms rotating on a circle and the occasional reorientation of the fourth hydrogen atom. [ 51–53 ]…”

Section: Resultsmentioning

confidence: 99%

See 1 more Smart Citation

High Hydrogen Mobility in an Amide–Borohydride Compound Studied by Quasielastic Neutron Scattering

et al. 2021

Self Cite

View full text Add to dashboard Cite

The hydrogen storage performance of reactive hydride composite Mg ( NH 2 ) 2 + 2 LiH can be significantly improved by the addition of LiBH 4 and the subsequent formation of an amide–borohydride compound Li 4 ( BH 4 ) ( NH 2 ) 3 during hydrogen release. Herein, an investigation into the structure and anion motions of Li 4 ( BH 4 ) ( NH 2 ) 3 using synchrotron radiation powder X‐ray diffraction (SR‐PXD; 295–573 K) and quasielastic neutron scattering (QENS; 297–514 K) is described. The highest temperature studied with QENS (514 K) is above the melting point of Li 4 ( BH 4 ) ( NH 2 ) 3 . The neutron measurements confirm a long‐range diffusive motion of hydrogen‐containing species with the diffusion coefficient D ≈ 10 − 6 cm 2 normals − 1 . Interestingly, this value is comparable to that of Li + diffusion inferred from conductivity measurements. SR‐PXD confirms the recrystallization of Li 4 ( BH 4 ) ( NH 2 ) 3 from the melt into the α‐phase upon cooling. At temperatures below 514 K, localized rotational motions are observed that are attributed to ( BH 4 ) − tetrahedra units mainly undergoing rotations around the C 3 axes. The activation energy for this thermally activated process is found to be E normala = 15.5 ± 0.9 and 17.4 ± 0.9 kJ mol − 1 respectively for the two instrumental resolutions utilized in the QENS measurements, corresponding to observation times of 55 and 14 ps.

show abstract

A quasielastic and inelastic neutron scattering study of the alkaline and alkaline-earth borohydrides LiBH₄ and Mg(BH₄)₂ and the mixture LiBH₄ + Mg(BH₄)₂

Abstract: Decomposition of the [BH4] dynamics in LiBH4 + Mg(BH4)2 according to the stoichiometric composition.

Cited by 18 publications

References 50 publications

Dynamics of porous and amorphous magnesium borohydride to understand solid state Mg-ion-conductors

Dynamics of porous and amorphous magnesium borohydride to understand solid state Mg-ion-conductors

High-resolution neutron spectroscopy using backscattering and neutron spin-echo spectrometers in soft and hard condensed matter

High Hydrogen Mobility in an Amide–Borohydride Compound Studied by Quasielastic Neutron Scattering

Contact Info

Product

Resources

About