Silicon is a promising candidate for the anode material in lithium ion batteries due to its ultrahigh theoretical capacity of 4200 mAh g(-1), which is approximately ten times larger compared to current commercial graphite anodes. However, the pulverization and capacity fading caused by the dramatic volume changes during cycling are still challenging its widespread application. To address these problems, a novel Si@C heterostructure with tunable preformed voids between Si core and carbon shell is synthesized via a flexible and tunable route. When evaluated for their electrochemical properties, these hollow Si@C spheres show enhanced electrochemical properties. (C) 2012 Elsevier Ltd. All rights reserved.