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

Abstract

The atomic structural stability and electronic properties of Li_nSn₄–carbon nanotube (CNT) and Li_nSn₄–graphene nanocomposites were studied by first principles calculations. Results on isolated Li_nSn₄ 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 Li_nSn₄ cluster weakly interacted with CNT as well as graphene for n ≤ 4, whereas a strong cation–π 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 Li_nSn₄–CNT imply that the volume change is minimal during lithiation and the average intercalation potential is estimated to be a maximum of ≈0.5 V, which shows its good anodic character.