The crystal structure and morphology of nanosized Si particles and wires after Li-insertion/extraction electrochemically have been studied by ex-situ XRD, Raman spectroscopy and electronic microscopy. It is confirmed that the insertion of lithium ions at room temperature destroys the crystal structure of Si gradually and leads to the formation of metastable amorphous Li-Si alloy, Furthermore, local ordered structure of Si can be restored after the partial extraction of lithium ions, which indicates the extraction of lithium ions promoting the recrystallization of amorphous Li-inserted Si. It was also observed that nanosized Si particles and wires were merged together after the insertion/extraction of lithium ions. (C) 2000 Elsevier Science B.V. All rights reserved.