Growth behavior and lithium storage performance of SnxCoy (x + y ≤ 7) clusters in double-layer graphene based on first-principles calculations.

The structural stability and lithium-storage properties of Snx and SnxCoy (x + y ≤ 7) clusters intercalated between bilayer graphene were systematically investigated via first-principles calculations based on DFT. In the Snx/BLG systems, the Sn4 cluster was found to exhibit superior structural stability through the combined analysis of formation energy and second-order difference energy. The Sn-C bond length in Snx clusters increased from 2.54 Å to 2.85 Å, accompanied by a marked intensification of carbon-layer distortion. Upon the introduction of Co atoms, among the SnxCoy clusters, SnCo and Sn4Co clusters were observed to exhibit the lowest formation energies and highest structural stability, thereby effectively mitigating atomic distortion of the bilayer graphene (BLG) carbon layers. The second-order difference energy (Δ2E) provides an effective criterion for evaluating the structural stability of intercalated clusters, enabling the screening of energetically stable Snx and SnxCoy cluster models. Lithium-storage calculations for SnCo and Sn4Co cluster intercalated BLG systems demonstrate that Li atoms are preferentially adsorbed around SnxCoy clusters and transfer charge to graphene layers. With increasing Li content, per-Li charge transfer decreases and inter-Li repulsion strengthens, reducing stability at high Li concentrations. Furthermore, Co doping strengthens the electronic coupling between the clusters and the graphene layers. In the Sn4Co/BLG system, Li insertion not only reduces the degree of localization of the density of states near the Fermi level but also enhances the conductivity of the system.