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.