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

TL;DR

This study uses first-principles calculations to analyze defect mechanisms in lithium alanate and how metal additives like Ti and Ni influence its decomposition and hydrogen release properties.

Contribution

It proposes an atomistic mechanism for LiAlH4 decomposition involving native defects and explains how metal impurities modify defect concentrations and kinetics.

Findings

Native defects facilitate mass transport during decomposition.

Ti and Ni impurities alter defect charge states and Fermi level.

The mechanism explains lowered decomposition temperature and activation energy.

Abstract

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