Micrometer-scale amorphous Si thin-film electrodes fabricated by electron-beam deposition for Li-ion batteries

A series of micrometer-scale Si thin films were fabricated by electron-beam deposition on the Cu substrate with specially treated concave-convex surface. The combined analyses involving scanning and transmission electron microscopy, selected area electron diffraction, and X-ray diffraction revealed that the deposited Si layer possessed good adhesion to the substrate and a discontinuous amorphous microstructure in which there existed large amounts of interface regions. The surface changes of the Si thin-film electrodes during Li insertion and extraction were investigated by glow discharge optical emission spectroscopy. The half-cell tests showed that these thicker films had higher capacity and more impressive cycleability relative to those reported in the literature; their cycleability could be substantially improved by limiting Li insertion depth. The full-cell tests indicated that Si films thicker than 4 mu m could provide sufficient capacity to match the standard LiCoO2 cathode with a similar to 70-mu m-thick coating layer. Such cells demonstrated small self-discharge rate as well as good cycling stability and efficiency in the long run, suggesting feasibility for potential practical applications. (c) 2006 The Electrochemical Society.