First-Principles Study of Lithiation of Type I Ba-Doped Silicon Clathrates

Silicon clathrate materials, previously known for their superconducting and thermoelectric characteristics, have also recently been investigated for their electrochemical properties as anodes for lithium-ion batteries due to their unique cage structure and ability to incorporate extrinsic guest atoms. To better understand the preferred structures for small degrees of lithiation, first-principles density functional theory (DFT) was used to investigate the type I clathrate compounds Si46, LixBaySi46 (0 ≤ x ≤ 8; y = 6, 8), and LixBayAl6Si40 (0 ≤ x ≤ 8; y = 6). The formation energies, electronic band structures, and density of states (DOS) were calculated. Lithium occupation in framework vacancies, empty and Ba-occupied cage cavities, and near the pentagonal and hexagonal faces of the clathrate polyhedra was considered. The data showed that Li insertion into framework or Ba vacancies could stabilize the clathrate structure. Silicon substitution by Al lowered the formation energies of the lithiated compounds a...