A novel Si/porous-C composite with buffering voids was prepared by the co-assembly of phenol-formaldehyde resin, SiO2 and Si nanoparticles, followed by a carbonizing process and subsequent removal of SiO2 template. Si nanoparticle was coated with a layer of porous carbon shell with rationally designed void in between which provides the accommodating space for the volume change of Si over cycling. The as-prepared composite electrode exhibited good electrochemical performances as an anode material in lithium-ion cells, showing a stable reversible capacity of 980 mAh g−1 over 80 cycles with small capacity fade of 0.17%/cycle and high rate capability (721mAhg−1 at 2000mAg−1).