Silicon and polypyrrole composites were synthesized using high-energy mechanical milling. The polypyrrole acts as a matrix to hold the active silicon grains as they repeatedly alloy with lithium during the operation of a lithium battery. Polypyrrole decreases the initial irreversible capacity loss of the silicon anode due to the reduction in the thickness of the solid electrolyte interface (SEI) layer formed. The composite containing 50 wt% silicon obtained after milling for 4 h exhibits a good reversibility, higher coulombic efficiency and better cycle life than the bare silicon. (c) 2005 Elsevier B.V All rights reserved.