Effect of Al on the dehydrogenation of LiBH4 from first-principles calculations

Al atom is designed to add into LiBH4 by occupation of Li atom, B atom and interstitial sites. The effects of Al on the dehydrogenation of LiBH4 are investigated by first-principles calculations. It is found that substitution with Al destabilizes LiBH4, leading to a reduction in the dehydrogenation energy (Ed) with the order of Li8B8H32 > Li8B7AlH32 > Li7AlB8H32 > Li8B8AlH32. This descending order is also reflected on the scaled bond order of BH (BOsBH) and the band gap (Eg). Our theoretical studies show that in LiBH4-Al systems, the weaker BH covalent bonding interaction, the metal-like character and the formation of AlB bond all favor H release. Al atom prefers to substitute for B atom, but this only weakly affects the dehydrogenation energy. Although Li8B8AlH32 compound with low dehydrogenation energy exhibits favorable dehydriding performance, the energy cost for Al occupation of interstitial site needs to be reduced for practical application.