Influence of dopants Ti and Ni on bonding interactions and dehydrogenation properties of lithium alanate

We report a study of the influence of Ti and Ni dopants on the stability and bonding interactions of LiAlH₄ using the first-principles method. Both the Ti and the Ni prefer to occupy an interstitial site in the LiAlH ₄ owing to lower occupation energies estimated from the total energy calculations. Calculations show that the bonding interactions between the Al and the H atoms within the [AlH₄] groups were significantly reduced by the dopants, and both the stability and the geometry of the [AlH₄] group were distorted in the doped LiAlH₄ systems. However, Ti and Ni use different mechanisms to improve the dehydrogenation properties of LiAlH ₄. The Ti dopant tends to interact with the Al atom in its neighbouring [AlH₄] to 'free' the H atoms from these [AlH ₄] groups. The effect of Ni dopant on the stability and the bonding interactions of the LiAlH₄ is due to the induction of the Ni d electrons that could cause a bonding interaction between the Ni and the Al atoms, strengthening the interactions between the Li and the H atoms, and 'freeing' the H atoms from the neighbouring [AlH₄] groups as well.