The monoammoniate of lithium borohydride (Li(NH 3 )BH 4 ) is a potential candidate for hydrogen storage owing to its high hydrogen capacity (18 wt%). In this work, electronic structure, bonding characters, and decomposition pathways of Li(NH 3 )BH 4 are investigated from first-principles calculations. We find that NH 3 molecules are covalently attached to Li atoms through N atoms and the ionization of Li atoms plays an essential role in stabilizing the compound. A general correlation between the stability of X(NH 3 )BH 4 (X=H,Li,Na,K) and the electronegativities of X atoms is established. The thermal stability of X(NH 3 )BH 4 could be modulated by manipulating the cation electronegativities. Free energy computations indicate that Li(NH 3 )BH 4 →LiBH 4 +NH 3 is the most likely thermal decomposition route.