Fundamental Aspects of Mechanical Dehydrogenation of Li- Based Complex Hydride Nanocomposites and Their Self-Discharge at Low Temperatures

Large quantities of hydrogen (H2) are released at ambient temperatures as a result of mechanical dehydrogenation during ball milling of complex hydride composites such as (LiAlH4+5 wt.% nanometric Fe), (nLiAlH4+LiNH2; n=1, 3, 11.5, 30), (nLiAlH4+MnCl2; n=1, 3, 8, 13, 30, 63) and (LiNH2+nMgH2; n=0.5-2.0). For both the (nLiAlH4+LiNH2) and (LiAlH4+5 wt.% nanometric Fe) composites the second constituent strongly destabilizes LiAlH4 during milling by different mechanisms. For (nLiAlH4+MnCl2) two concurrent mechanisms are observed: (i) a reaction between both constituents during ball milling leading to the formation of LiCl, amorphous Mn and H2, and (ii) a catalytic-like induced decomposition of LiAlH4 into Li3AlH6, Al and H2. For the (LiNH2+nMgH2; 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 H2 at room temperature (RT), 40 and 80 °C, after ball milling with an additive. Technical parameters such as specific energy-usable are estimated for LiAlH4-based complex hydride composite systems and are compared with both US DOE hydrogen powered car targets and Li-ion batteries benchmarks.