Abstract
Anion substitution is at present one of the pathways to destabilize metal borohydrides for solid state hydrogen storage. In this work, a solid solution of LiBH4 and LiCl is studied by density functional theory (DFT) calculations, thermodynamic modeling, X-ray diffraction, and infrared spectroscopy. It is shown that Cl substitution has minor effects on thermodynamic stability of either the orthorhombic or the hexagonal phase of LiBH4. The transformation into the orthorhombic phase in LiBH4 shortly after annealing with LiCl is for the first time followed by infrared measurements. Our findings are in a good agreement with an experimental study of the LiBH4-LiCl solid solution structure and dynamics. This demonstrates the validity of the adopted combined theoretical (DFT calculations) and experimental (vibrational spectroscopy) approach, to investigate the solid solution formation of complex hydrides.
Highlights
Mixtures of metal borohydrides with halides have recently evoked careful attention as candidates for hydrogen storage materials [1,2,3,4,5,6,7] and novel solid-state lithium electrolytes [8,9,10,11]
We present the study on the LiBH4-LiCl system, utilizing attenuated total reflection infrared spectroscopy (IR-ATR), powder X-ray diffraction (PXRD), density functional theory (DFT) calculations with CRYSTAL
The Cl− content in LiBH4 is strongly reduced and LiCl is formed The Cl− content in the orthorhombic phase (x = 0.10), observed in PXRD measurements, is in agreement with previous experiments [12], but it turns out higher than that predicted by combined ab initio and CALPHAD
Summary
Mixtures of metal borohydrides with halides have recently evoked careful attention as candidates for hydrogen storage materials [1,2,3,4,5,6,7] and novel solid-state lithium electrolytes [8,9,10,11]. Periodic ab initio CRYSTAL code [16] has already been successfully applied in a number of studies dealing with the computational prediction of solid solution formation, both for simple and complex hydrides [2,17]. We present the study on the LiBH4-LiCl system, utilizing attenuated total reflection infrared spectroscopy (IR-ATR), powder X-ray diffraction (PXRD), DFT calculations with CRYSTAL code and thermodynamic modeling
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