Synergism of Rare Earth Trihydrides and Graphite in Lithium Storage: Evidence of Hydrogen-Enhanced Lithiation.

The lithium storage capacity of graphite can be significantly promoted by rare earth trihydrides (REH3 , RE = Y, La, and Gd) through a synergetic mechanism. High reversible capacity of 720 mA h g-1 after 250 cycles is achieved in YH3 -graphite nanocomposite, far exceeding the total contribution from the individual components and the effect of ball milling. Comparative study on LaH3 -graphite and GdH3 -graphite composites suggests that the enhancement factor is 3.1-3.4 Li per active H in REH3 , almost independent of the RE metal, which is evident of a hydrogen-enhanced lithium storage mechanism. Theoretical calculation suggests that the active H from REH3 can enhance the Li+ binding to the graphene layer by introducing negatively charged sites, leading to energetically favorable lithiation up to a composition Li5 C16 H instead of LiC6 for conventional graphite anode.