In situ formation of lithium fast-ion conductors and improved hydrogen desorption properties of the LiNH2–MgH2 system with the addition of lithium halides

Abstract

Lithium halides were introduced into the LiNH₂–MgH₂ system by ball milling the corresponding chemicals under 50 bar of H₂ to decrease the dehydrogenation temperature and enhance the dehydrogenation kinetics. The results show that the LiNH₂–MgH₂–0.05LiBr sample exhibited optimal hydrogen storage performance. The onset dehydrogenation temperature of the LiNH₂–MgH₂–0.05LiBr sample was only 120 °C, which represents a 55 °C reduction with respect to that of the pristine LiNH₂–MgH₂ sample. The dehydrogenation rate of the LiNH₂–MgH₂ sample at 210 °C was increased threefold upon addition of LiBr, which is attributed to the reduction in the dehydrogenation activation energy. Moreover, the addition of LiBr could significantly suppress ammonia emission during the dehydrogenation process of the LiNH₂–MgH₂ sample. Structural examinations reveal that the added LiBr could react with LiNH₂ to form Li₇(NH₂)₆Br during the dehydrogenation process. The in situ-formed Li₇(NH₂)₆Br not only weakens the N–H bond but also promotes the migration of Li⁺, consequently improving the dehydrogenation kinetics of the LiNH₂–MgH₂ sample.