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

Published

October 8, 2024

Author(s)

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

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 Å2 for NH2, 1.503 Å2 for CH3, and 1.856 Å2 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.

Citation

Chemistry of Materials

Volume

36

Issue

19

Pub Type

Journals

Download Paper

https://doi.org/10.1021/acs.chemmater.4c01947

Local Download

Keywords

neutron scattering, solid-state electrolytes, borohydrides

Citation

Amdisen, M. , Cheng, Y. , Jalarvo, N. , Pajerowski, D. , Brown, C. , Jensen, T. and Andersson, M. (2024), The Influence of Reorientational and Vibrational Dynamics on the Mg2+ Conductivity in Mg(BH4)2·CH3NH2, Chemistry of Materials, [online], https://doi.org/10.1021/acs.chemmater.4c01947, https://tsapps.nist.gov/publication/get_pdf.cfm?pub_id=958187 (Accessed July 12, 2025)