A promising anode material for Li-ion batteries based on MgH2 with around 5 nm average particle size was synthesized by a bottom-up method.

MgH2, Mg-Ni-H and Mg-Fe-H nanoparticles inserted into ordered mesoporous carbon templates have been synthesized by decomposition of organometallic precursors under hydrogen atmosphere and mild temperature conditions. The hydrogen desorption properties of the MgH2 nanoparticles are studied by thermo-desorption spectroscopy. The particle size distribution of MgH2, as determined by TEM, is crucial for understanding the desorption properties. The desorption kinetics are significantly improved by downsizing the particle size below 10 nm. Isothermal absorption/desorption cycling of the MgH2 nanoparticles shows a stable capacity over 13 cycles. The absorption kinetics are unchanged though the desorption kinetics are slower on cycling.

The formation of ultra-small Mg-based particles nanoconfined into the mesopores of a carbon template was studied by in situ synchrotron diffraction. Either Mg 2 Ni or Mg 2 NiH 4 nanoparticles can be directly formed starting from separate Ni and MgH 2 species by tuning the H 2 pressure. Both ultra-small Mg 2 Ni and Mg 2 NiH 4 nanoparticles (~4 nm) are extremely stable against coalescence during hydrogen sorption cycling and prolonged exposure to high temperature as compared to Mg and MgH 2 nanoparticles that show severe coalescence under same experimental conditions. The structural transition reported in bulk Mg 2 NiH 4 from high temperature cubic to low temperature monoclinic structure is no longer observed for the nanoconfined particles. Hydrogen absorption/desorption in nanosized Mg 2 Ni is reversible and desorption kinetics from Mg 2 NiH 4 proceeds very quickly (~5 min) even at 483 K. On the contrary, the thermodynamics properties are not altered by nanoconfinement. This study opens new routes for successful nanoconfinement of stoichiometric hydrides into the pores of carbon hosts along with a better understanding of nanochemistry.