  We report first-principles density functional theory studies of native
defects in lithium borohydride (LiBH$_{4}$), a potential material for hydrogen
storage. Based on our detailed analysis of the structure, energetics, and
migration of lithium-, boron-, and hydrogen-related defects, we propose a
specific mechanism for the decomposition and dehydrogenation of LiBH$_{4}$ that
involves mass transport mediated by native defects. In this mechanism,
LiBH$_{4}$ releases borane (BH$_{3}$) at the surface or interface, leaving the
negatively charged hydrogen interstitial (H$_{i}^{-}$) in the material, which
then acts as the nucleation site for LiH formation. The diffusion of
H$_{i}^{-}$ in the bulk LiBH$_{4}$ is the rate-limiting step in the
decomposition kinetics. Lithium vacancies and interstitials have low formation
energies and are highly mobile. These defects are responsible for maintaining
local charge neutrality as other charged defects migrating along the material,
and assisting in the formation of LiH. In light of this mechanism, we discuss
the effects of metal additives on hydrogen desorption kinetics.
