Effects of a Carbon Surface Environment on the Decomposition Properties of Nanoparticle LiBH4: A First-Principles Study

We present a first-principles study of small clusters of LiBH4 supported on graphene sheets in order to address the experimentally observed effects of the nanoconfinement of LiBH4 in hard carbon nanoframeworks prepared from low-temperature pyrolysis of phenolic resins, where a fullerene-related structure with significant sp(2) character is known to exist. Our results indicate that the wetting of carbon by LiBH4, as observed in experiments, is not energetically favorable without the introduction of boron substitution defects in the graphene sheet. The simplest defect, consisting of a carbon vacancy, introduces favorable wetting energies via the partial decomposition of LiBH4. Heteroatom boron in place of the carbon vacancies interacts with lithium and small clusters of the remaining LiBH4, making wetting of these clusters favorable. It is also predicted that the desorption product LiH will be ejected from the framework, in agreement with recent in situ TEM work.