Structural stability and bonding nature of Li-Sn-carbon nanocomposites as Li-ion battery anodes: first principles approach

The atomic structural stability and electronic properties of LinSn4-carbon nanotube (CNT) and LinSn4-graphene nanocomposites were studied by first principles calculations. Results on isolated LinSn4 clusters, with n = 0-10, revealed that the tetrahedron shaped Li4Sn4 Zintl cluster is the most stable owing to it having high symmetry as well as a largest highest occupied molecular orbital-lowest unoccupied molecular orbital (HOMO-LUMO) gap. This LinSn4 cluster weakly interacted with CNT as well as graphene for n <= 4, whereas a strong cation-pi interaction is observed between them for n > 4 which significantly reduces the Li clustering. The interaction between the Sn cluster and CNT or graphene is mediated only through Li ions whose absence destabilizes the Sn-C composite. These results were further confirmed by electronic density of states and band structure calculations. In addition, our calculations on hexagonal assembly of LinSn4-CNT imply that the volume change is minimal during lithiation and the average intercalation potential is estimated to be a maximum of approximate to 0.5 V, which shows its good anodic character.