The mechanism of Mg 2+ conduction in ammine magnesium borohydride promoted by a neutral molecule

DOI: 10.1039/D0CP00158A

Authors: Yigang Yan (Aarhus University; Sichuan University) , Wilke Dononelli (Aarhus University) , Mathias Jorgensen (University of Aarhus) , Jakob B. Grinderslev (University of Aarhus) , Young-su Lee (Korea Institute of Science and Technology) , Young Whan Cho (Korea Institute of Science and Technology) , Radovan Cerny (University of Geneva) , Bjørk Hammer (Aarhus University) , Torben R. Jensen (Aarhus University)
Co-authored by industrial partner: No

Type: Journal Paper
Journal: Physical Chemistry Chemical Physics , VOL 66

State: Published (Approved)
Published: March 2020

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 monoammine magnesium borohydride, Mg(BH4)2·NH3. Density functional theory calculations (DFT) reveal that the neutral molecule (NH3) in Mg(BH4)2·NH3 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+⋯−δH–B and the versatile coordination of the BH4− ligand. DFT shows that di-hydrogen bonds in inorganic matter and hydrogen bonds in bio-materials have similar bond strengths and bond lengths. As a result of the high structural flexibiliy, the Mg-ion conductivity is dramatically 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 magnitude higher than that of Mg(BH4)2. Our results may inspire a new approach for the design and discovery of unprecedented multivalent ion conductors.

Subject Areas: Chemistry, Energy


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