Based on the density functional theory, we study the insertion of Li and Na atoms into both bulk Sn and Sn(111) nanosheets. Analysis of the bonding between the metal atoms and the Sn systems shows that the interactions have significant ionicity-the electron charge reductions on the metal atoms are up to similar to 0.87e. We predict that the diffusion of the metal atoms at the nanosheet surface is much faster than in bulk Sn, and, consequently, the bulk-nanosheet transition is expected to facilitate the migration of the metal atoms and might improve the charge/discharge rate of Sn anode materials. We also show that size reduction affects the energetics of subsurface layers. For instance, for both Li and Na, the lowest defect formation energies inside a 6-layer Sn(111) nanosheet are similar to 0.24 eV larger than those in the bulk Sn. The analysis of Li and Na insertion pathways and barriers into a 6-layer Sn(111) nanosheets shows that the insertion into Sn nanosheets is energetically and kinetically more favorable than insertion into Si systems. (C) 2014 Elsevier B.V. All rights reserved.