Nanoscaled tin (Sn) particles were embedded in the mesopores of hard carbon spherules (HCS) to form a composite anode material for lithium ion batteries. The structure of the obtained composite was characterized by X-ray diffraction (XRD) and the electrochemical performances were evaluated by galvanostatic cycling and cyclic voltammetry. It is found that embedding Sn nanoparticles into HCS not only results in a composite material with high-lithium storage capacity and capacity retention, but also increases the initial coulombic efficiency of the composite. Based on the infrared spectroscopic analysis, the enhanced initial coulombic efficiency is attributed to the nano-tin-induced decomposition of the ROCO2Li. species in the solid electrolyte interphase (SEI) layer. (c) 2007 Elsevier B.V. All rights reserved.