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 Li₅C₁₆H instead of LiC₆ for conventional graphite anode.