The Influence of Reorientational and Vibrational Dynamics on the Mg2+ Conductivity in Mg(BH4)2·CH3NH2

Mads B. Amdisen; Yongqiang Cheng; Niina Jalarvo; Daniel Pajerowski; Craig M. Brown; Torben R. Jensen; Mikael S. Andersson

doi:10.1021/acs.chemmater.4c01947

The Influence of Reorientational and Vibrational Dynamics on the Mg²⁺ Conductivity in Mg(BH₄)₂·CH₃NH₂

Mads B. Amdisen, Yongqiang Cheng, Niina Jalarvo, Daniel Pajerowski, Craig M. Brown, Torben R. Jensen, Mikael S. Andersson

Research output: Contribution to journal › Article › peer-review

Abstract

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(BH₄)₂·CH₃NH₂) 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 BH₄^- anion compared to Mg(BH₄)₂. This is likely part of the explanation for the high Mg-ion transport observed for Mg(BH₄)₂·CH₃NH₂. Furthermore, while the dynamics of both the BH₄^- anion and the CH₃ group of the methylamine ligand is rapid, the NH₂ 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 A² for NH₂, 1.503 A² for CH₃, and 1.856 A² for BH₄^- 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.

Original language	English
Pages (from-to)	9784-9792
Number of pages	9
Journal	Chemistry of Materials
Volume	36
Issue number	19
DOIs	https://doi.org/10.1021/acs.chemmater.4c01947
State	Published - Oct 8 2024

Funding

This research used resources at the Spallation Neutron Source, a DOE Office of Science User Facility operated by the Oak Ridge National Laboratory. The beam times were allocated to VISION on proposal number IPTS-29876.1, to BASIS on proposal number IPTS-29793.1, and to CNCS on proposal number IPTS-29866.1. This research used computing resources made available through the VirtuES and the ICE-MAN projects, funded by Laboratory Directed Research and Development program and Compute and Data Environment for Science (CADES) at Oak Ridge National Laboratory, as well as resources of National Energy Research Scientific Computing Center (NERSC), a U.S. Department of Energy Office of Science User Facility located at Lawrence Berkeley National Laboratory, operated under Contract No. DE-AC02-05CH11231 using NERSC award ERCAP0024340. This work was carried out with the support of Diamond Light Source, instrument I11 (proposal CY26090). M.S.A. acknowledges the support from the \u00C5Forsk Foundation (21-453), the Magnus Bergvall Foundation and the Go\u0308ran Gustafsson Foundation. The work was supported by the Danish Council for Independent Research, Nature and Universe (Danscatt), and Technology and Production (CaMBat, DFF 0217-00327B). Affiliation with the Center for Integrated Materials Research (iMAT) at Aarhus University is gratefully acknowledged. Funding from the Danish Ministry of Higher Education and Science through the SMART Lighthouse is gratefully acknowledged. Certain trade names and company products are identified in order to specify adequately the experimental procedure. In no case does such identification imply recommendation or endorsement by the National Institute of Standards and Technology, nor does it imply that the products are necessarily the best for the purpose.

Funders	Funder number
Magnus Bergvalls Stiftelse
Oak Ridge National Laboratory
Göran Gustafssons Stiftelser
SMART Lighthouse
Laboratory Directed Research and Development
Office of Science
Ministry of Science and Higher Education of the Russian Federation
Lawrence Berkeley National Laboratory	DE-AC02-05CH11231, CY26090, ERCAP0024340
Lawrence Berkeley National Laboratory
Stiftelsen Åforsk	21-453
Stiftelsen Åforsk
Danish Council for Independent Research, Nature and Universe	DFF 0217-00327B

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title = "The Influence of Reorientational and Vibrational Dynamics on the Mg2+ Conductivity in Mg(BH4)2·CH3NH2",

abstract = "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(BH4)2·CH3NH2) 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 BH4- anion compared to Mg(BH4)2. This is likely part of the explanation for the high Mg-ion transport observed for Mg(BH4)2·CH3NH2. Furthermore, while the dynamics of both the BH4- anion and the CH3 group of the methylamine ligand is rapid, the NH2 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 A2 for NH2, 1.503 A2 for CH3, and 1.856 A2 for BH4- 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.",

author = "Amdisen, {Mads B.} and Yongqiang Cheng and Niina Jalarvo and Daniel Pajerowski and Brown, {Craig M.} and Jensen, {Torben R.} and Andersson, {Mikael S.}",

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AU - Pajerowski, Daniel

AU - Brown, Craig M.

AU - Jensen, Torben R.

AU - Andersson, Mikael S.

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The Influence of Reorientational and Vibrational Dynamics on the Mg²⁺ Conductivity in Mg(BH₄)₂·CH₃NH₂

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