Li-Filled, B‑Substituted Carbon Clathrates

Inside the cages of hypothetical
carbon clathrates there is precious
little room, even for the smallest atoms, such as Liunless
it is the Li+ ion that is inserted, in which case a compensating
negative charge should be distributed over the carbon cage. The hypothesis
explored in this paper is that Li insertion can be achieved with appropriate
B substitution within the framework. The resulting structures of 2Li@C10B2 (Clathrate VII), 8Li@C38B8 (Clathrate I), 7Li@C33B7 (Clathrate IV), 6Li@C28B6 (Clathrate H), and 6Li@C28B6 (Clathrate II) are definitely stabilized in theoretical calculations,
especially under elevated pressure, as judged by enthalpy criteria
and bond length metrics. Different strategies for B substitution (symmetry
reduction, following the parent charge distribution, and substitution
on the most weakened bonds, relieving stress on bond angles) are explored.
Two possible competing channels for Li doping–B substitution,
formation of LiBC and C-vacancies, are investigated.