Amdisen Mads B, Cheng Yongqiang, Jalarvo Niina, Pajerowski Daniel, Brown Craig M, Jensen Torben R, Andersson Mikael S
Interdisciplinary Nanoscience Center (iNANO) and Department of Chemistry, University of Århus, Langelandsgade 140, Århus C DK-8000, Denmark.
Neutron Scattering Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, United States.
Chem Mater. 2024 Sep 16;36(19):9784-9792. doi: 10.1021/acs.chemmater.4c01947. eCollection 2024 Oct 8.
Reorientational dynamics in solid electrolytes can significantly enhance the ionic conductivity, and understanding these dynamics can facilitate the rational design of improved solid electrolytes. Additionally, recent investigations on metal hydridoborate-based solid electrolytes have shown that the addition of a neutral ligand can also have a positive effect on the ionic conductivity. In this study, we investigate the dynamics in monomethylamine magnesium borohydride (Mg(BH)·CHNH) with quasielastic and inelastic neutron scattering, density functional theory calculations, and molecular dynamics simulations. The results suggest that the addition of methylamine significantly speeds up the reorientational frequency of the BH anion compared to Mg(BH). This is likely part of the explanation for the high Mg-ion transport observed for Mg(BH)·CHNH. Furthermore, while the dynamics of both the BH anion and the CH group of the methylamine ligand is rapid, the NH group of the methylamine ligand exhibits much slower reorientations, as confirmed by both experimental and computational investigations. Notably, molecular dynamics calculations reveal mean square displacements of 0.387 Å for NH, 1.503 Å for CH, and 1.856 Å for BH using a trajectory of 10 ps. This study confirms the simultaneous presence of fast dynamics and high ionic conductivity in a metal borohydride-based system and can function as an experimental foundation for future studies on dynamics in hydrogen-rich solid electrolytes.
固体电解质中的重取向动力学可显著提高离子电导率，理解这些动力学有助于合理设计性能更优的固体电解质。此外，最近对金属氢硼酸盐基固体电解质的研究表明，添加中性配体也可对离子电导率产生积极影响。在本研究中，我们利用准弹性和非弹性中子散射、密度泛函理论计算以及分子动力学模拟，研究了一甲胺硼氢化镁（Mg(BH₄)₂·CH₃NH₂）中的动力学。结果表明，与Mg(BH₄)₂相比，甲胺的添加显著加快了BH₄⁻阴离子的重取向频率。这可能是Mg(BH₄)₂·CH₃NH₂中观察到高镁离子传输现象的部分原因。此外，实验和计算研究均证实，虽然BH₄⁻阴离子和甲胺配体的CH₃基团动力学很快，但甲胺配体的NH₂基团重取向要慢得多。值得注意的是，分子动力学计算显示，使用10 ps的轨迹，NH₂的均方位移为0.387 Å，CH₃为1.503 Å，BH₄⁻为1.856 Å。本研究证实了基于金属硼氢化物的体系中同时存在快速动力学和高离子电导率，可为未来富氢固体电解质动力学研究提供实验基础。
