Sub-Ambient Fast Magnesium Ionic Conductivity in Diethylamine Magnesium Tetrahydridoborate and Its Crystal Structure
- 1Interdisciplinary Nanoscience Center (iNANO) and Department of Chemistry, Aarhus University, Langelandsgade 140, 8000 Aarhus C, Denmark
Abstract
Magnesium tetrahydridoborate derivatives are promising electrolytes for next-generation solid-state batteries due to their high Mg2+ conductivity and stability towards magnesium metal. Here, we report the synthesis, crystal structure and thermal properties of mono-diethylamine magnesium tetrahydridoborate, Mg(BH4)2∙NH(CH2CH3)2, and the ionic conductivity of the composite Mg(BH4)2∙NH(CH2CH3)2−60wt% Al2O3. Synchrotron radiation powder X-ray diffraction data combined with ab initio structure determination and density functional theory reveal a monoclinic structure (P21/c) comprising one-dimensional zig-zag chains interconnected by dihydrogen bonds and dispersive interactions between organic moieties (–CH2CH3). The compound melts at 83 °C and begins to decompose at 116 °C. Owing to their soft and malleable nature, 60wt% Al2O3 nanoparticles (13 nm) were incorporated to provide mechanical stability, which stabilizes the soft electrolyte while preserving thermal stability. Electrochemical impedance spectroscopy of the composite Mg(BH4)2∙NH(CH2CH3)2−60wt% Al2O3 demonstrates exceptionally high ionic conductivity, reaching σ = 2.58 × 10−6 S cm−1 at −2 °C and crossing 10−4 S cm−1 below 40 °C with an activation energy of 695 ± 11 meV, representing one of the highest conductivities reported for a magnesium hydridoborate derivative. The conductivity decreases significantly when heated above 40 °C, suggesting that slow drying is occurring. This is supported by a decrease in conductivity upon long-term storage. These results highlight the potential of ligand-mediated structural flexibility in enabling highly conductive magnesium solid electrolytes for near room-temperature solid-state inorganic batteries.
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BibTeX
@article{ortoft2026subambient,
title = {{Sub-Ambient Fast Magnesium Ionic Conductivity in Diethylamine Magnesium Tetrahydridoborate and Its Crystal Structure}},
author = {Oliver G. Ørtoft and Lasse R. Kristensen and Torben R. Jensen},
journal = {Inorganics},
year = {2026},
month = oct,
doi = {10.3390/inorganics14110279},
url = {https://www.mdpi.com/2304-6740/14/11/279},
note = {CC BY 4.0},
}
RIS
TY - JOUR
TI - Sub-Ambient Fast Magnesium Ionic Conductivity in Diethylamine Magnesium Tetrahydridoborate and Its Crystal Structure
AU - Oliver G. Ørtoft
AU - Lasse R. Kristensen
AU - Torben R. Jensen
PY - 2026
DA - 2026/10/29
JO - Inorganics
DO - 10.3390/inorganics14110279
UR - https://www.mdpi.com/2304-6740/14/11/279
AB - Magnesium tetrahydridoborate derivatives are promising electrolytes for next-generation solid-state batteries due to their high Mg2+ conductivity and stability towards magnesium metal. Here, we report the synthesis, crystal structure and thermal properties of mono-diethylamine magnesium tetrahydridoborate, Mg(BH4)2∙NH(CH2CH3)2, and the ionic conductivity of the composite Mg(BH4)2∙NH(CH2CH3)2−60wt% Al2O3. Synchrotron radiation powder X-ray diffraction data combined with ab initio structure determination and density functional theory reveal a monoclinic structure (P21/c) comprising one-dimensional zig-zag chains interconnected by dihydrogen bonds and dispersive interactions between organic moieties (–CH2CH3). The compound melts at 83 °C and begins to decompose at 116 °C. Owing to their soft and malleable nature, 60wt% Al2O3 nanoparticles (13 nm) were incorporated to provide mechanical stability, which stabilizes the soft electrolyte while preserving thermal stability. Electrochemical impedance spectroscopy of the composite Mg(BH4)2∙NH(CH2CH3)2−60wt% Al2O3 demonstrates exceptionally high ionic conductivity, reaching σ = 2.58 × 10−6 S cm−1 at −2 °C and crossing 10−4 S cm−1 below 40 °C with an activation energy of 695 ± 11 meV, representing one of the highest conductivities reported for a magnesium hydridoborate derivative. The conductivity decreases significantly when heated above 40 °C, suggesting that slow drying is occurring. This is supported by a decrease in conductivity upon long-term storage. These results highlight the potential of ligand-mediated structural flexibility in enabling highly conductive magnesium solid electrolytes for near room-temperature solid-state inorganic batteries.
SN - 2304-6740
ER -