High hydrogen content super-lightweight intermetallics from the Li–Mg–Si system

The existence of Li-rich super-lightweight intermetallics in the Li–Mg–Si ternary system has attracted attention for high capacity hydrogen storage materials. The hydrogenation properties of the alloys were studied by thermogravimetric analysis, differential scanning calorimetry in H2 atmosphere and X-ray diffraction. The Li-rich alloy absorbs the highest amount of hydrogen (8.8% w/w for Li70Mg10Si20), while the Mg-rich alloy (Li30Mg40Si30) absorbs 6.0% w/w H2 and shows the first experimental evidence for LiMgH3 formation with LiNbO3-type structure during hydrogenation.The extension of homogeneity range of existing phases from Li–Mg–Si system was found and the crystal structures of four ternary phases, Li2+xMg1−xSi (x = 0.268), Li65−x+yMg30+x−ySi33 (x = 9.15, y = 1.23), Li7−x+yMg5+x−ySi4 (x = 1.14, y = 0.61) and Lix+yMg2−xSi (x = 0.51, y = 0.39), were solved and more precise refined using X-ray single crystal diffraction data. Electronic structure calculations reveal an increased occupation of electronic states at the Fermi level for Li12+xMg3−xSi4 in comparison to Li2+xMg1−xSi. The results of crystal orbital Hamilton population (COHP) and integrated crystal orbital Hamilton population (iCOHP) calculations for both structures indicate the strongest interactions between Mg–Si (-iCOHP = 1.999 eV) and the weakest between Li–Li (-iCOHP = 0.049 eV).

Graphical abstractFigure optionsDownload full-size imageDownload as PowerPoint slideHighlights► Hydrogenation properties of ternary phases from the Li–Mg–Si system were established. ► The crystal structures of five phases were determined. ► The electronic structures of four phases were calculated. ► The highest amount of hydrogen absorbed by the Li-rich alloy is equal 8.8% w/w.