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The Mechanism of Mg2+ Conductivity in Ammine Magnesium Borohydride Promoted by a Neutral Molecule

Abstract

Light weight and cheap electrolytes with fast multi-valent ion conductivity can pave the way for future high-energy density solid-state batteries, beyond the lithium-ion battery. Here we present the mechanism of Mg-ion conductivity of ammine magnesium borohydrides, Mg(BH4)2·xNH3 (x = 1, 2, 3, 6). Density functional theory calculations (DFT) reveal that the neutral molecule (NH3) in Mg(BH4)2·xNH3 is exchanged between the lattice and interstitial Mg2+ facilitated by a highly flexible structure, mainly owing to a network of di-hydrogen bonds, N-Hδ+...H-B and the versatile coordination of the BH4- ligand. As a result, the Mg-ion conductivity is dramastically improved at moderate temperature, e.g. σ(Mg2+) = 3.3×10–4 S cm–1 at T = 80 °C for Mg(BH4)2·NH3, which is approximately 8 orders of magtitude higher than that of Mg(BH4)2. Our results may inspire a new approach for design and discovery of unprecedented multivalent ion conductors.

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Supplementary files

Article information


Submitted
10 Jan 2020
Accepted
23 Mar 2020
First published
23 Mar 2020

Phys. Chem. Chem. Phys., 2020, Accepted Manuscript
Article type
Paper

The Mechanism of Mg2+ Conductivity in Ammine Magnesium Borohydride Promoted by a Neutral Molecule

Y. Yan, W. Dononelli, M. Jørgensen, J. B. Grinderslev, Y. Lee, Y. W. Cho, R. Cerny, B. Hammer and T. R. R. Jensen, Phys. Chem. Chem. Phys., 2020, Accepted Manuscript , DOI: 10.1039/D0CP00158A

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