Silicon and titanium boride nanocomposites were synthesized using high-energy mechanical milling. The nanocomposites obtained after mechanical milling consist of amorphous silicon and nanocrystalline titanium boride. The nanocomposite containing 40 mol % silicon obtained after milling for 20 h exhibits a stable capacity of similar to400 mAh/ g. X- ray diffraction and scanning electron microscopy analyses indicated that the nanocomposite retains its initial phase and microstructure during electrochemical cycling. Premilling of the inactive TiB2 component appears to increase the stability of the capacity of the nanocomposite electrodes due to a probable homogeneous distribution of the induced stress during cycling. (C) 2003 The Electrochemical Society.