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PRINCIPAL PUBLICATION AND AUTHORS

Structural insight into the magnesium borohydride-ethylenediamine solid-state Mg-ion electrolyte system, I.E. Golub (a), M. Heere (b,c), V. Gounaris (a), X. Li (a), T. Steenhaut (a), J. Wang (a), K. Robeyns (a), H.-W. Li (d), I. Dovgaliuk (e,f), K. Ikeda (g), G. Hautier (a), Y. Filinchuk (a), Dalton Trans. 52(8), 2404-2411 (2023); https:/doi.org/10.1039/D2DT03567G (a) Institute of Condensed Matter and Nanosciences (IMCN), Université catholique de Louvain (UCLouvain), Louvain-la-Neuve (Belgium) (b) Institute for Applied Materials Energy Storage Systems (IAM-ESS), Karlsruhe Institute of Technology (KIT), Eggenstein (Germany) (c) Technische Universität Braunschweig, Institute of Internal Combustion Engines, Braunschweig (Germany) (d) Hefei General Machinery Research Institute (HGMRI), Hefei (China) (e) Swiss Norwegian Beamlines, ESRF, Grenoble (France) (f) Institut des Matériaux Poreux de Paris, Ecole Normale Supérieure, Paris (France) (g) Institute of Materials Structure Science, High Energy Accelerator Research Organization (KEK), Tsukuba (Japan)

REFERENCES

[1] S. Payandeh, A. Remhof & C. Battaglia, in Magnesium Batteries: Research and Applications, Maximilian Fichtner (ed.), The Royal Society of Chemistry (Cambridge, UK), 60- 78 (2020). [2] E. Roedern et al., Sci. Rep. 7, 46189 (2017). [3] O.A. Babanova et al., Solid State Ionics 397, 116232 (2023).

Fig. 69: Fragment of the crystal structure of Mg(en)2(BH4)2. Colour code: Mg: aquamarine; N: blue; B: olive; C: grey; H: white.

Furthermore, variable-temperature X-ray powder diffraction complemented by density functional theory optimisation revealed that Mg5(en)6(BH4)10 transforms into another phase upon heating, with a stoichiometry hitherto unobserved within the magnesium borohydride- ethylenediamine system Mg(en)2(BH4)2 (Figure 69). The data suggest that the formation of the crystalline Mg(en)2(BH4)2 is accompanied by the formation of amorphous Mg(BH4)2. The amorphous phase also forms upon mechano-chemical synthesis, decreasing the conductivity of the samples, but it is omitted in the phase analysis made by X-ray diffraction.

In summary, new insights into the structural complexity of the magnesium borohydride-ethylenediamine solid-state electrolyte system were obtained through synchrotron X-ray and neutron diffraction. The existence of Mg5(en)6(BH4)10 and Mg(en)2(BH4)2, which results from thermal decomposition of the former, were evidenced for the first time. The surprising voids observed in the structure of Mg5(en)6(BH4)10 might be fundamental to its conductivity. The results of this study, including comprehending the role of the amorphous Mg(BH4)2, are key to the further understanding and enhancement of solid-state electrolytes for MIBs and are further investigated by nuclear magnetic resonance (NMR) [3].