Decomposition mechanism and the effects of metal additives on the kinetics of lithium alanate

摘要

First-principles density functional theory studies have been carried out fornative defects and transition-metal (Ti and Ni) impurities in lithium alanate(LiAlH$_{4}$), a potential material for hydrogen storage. On the basis of ourdetailed analysis of the structure, energetics, and migration of lithium-,aluminum-, and hydrogen-related defects, we propose a specific atomisticmechanism for the decomposition and dehydrogenation of LiAlH$_{4}$ thatinvolves mass transport mediated by native point defects. We also discuss howTi and Ni impurities alter the Fermi-level position with respect to that in theundoped material, thus changing the concentration of charged defects that areresponsible for mass transport. This mechanism provides an explanation for theexperimentally observed lowering of the temperature for the onset ofdecomposition and of the activation energy for hydrogen desorption fromLiAlH$_{4}$.