Fundamental aspects of mechanical dehydrogenation of Li-based complex hydride nanocomposites and their self-discharge at low temperatures

摘要

Large quantities of hydrogen (H_2) are released at ambient temperatures as a result of mechanical dehydrogenation during ball milling of complex hydride composites such as (UAlH4＋5 wt.% nanometric Fe), (nLiAlH_4＋LiNH_2; n=1, 3, 11.5, 30), (nLiAlH_4+MnCl_2; n=1, 3, 8, 13, 30, 63) and (LiNH_2＋nMgH_2; n=0.5-2.0). For both the (nLiAlH_4＋LiNH_2) and (LiAlH_4＋5 wt.% nanometric Fe) composites the second constituent strongly destabilizes LiAlH_4 during milling by different mechanisms. For (nLiAlH4＋MnCl_2) two concurrent mechanisms are observed: (ⅰ) a reaction between both constituents during ball milling leading to the formation of LiCl, amorphous Mn and H_2, and (ⅱ) a catalytic-like induced decomposition of LiAlH_4 into Li_3AlH_6, Al and H_2. For the (LiNH_2＋nMgH_2; n=0.5-2.0) composite system, the pathway of hydride reactions depends on the molar ratio n and total milling energy consumed during ball milling. Some composite systems slowly self-discharge H_2 at room temperature (RT), 40 and 80°C, after ball milling with an additive. Technical parameters such as specific energy-usable are estimated for LiAlH_4-based complex hydride composite systems and are compared with both US DOE hydrogen powered car targets and Li-ion batteries benchmarks.