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 m could provide sufficient capacity to match the standard LiCoO 2 cathode with a ϳ70-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.
The Ag-Sn alloys prepared by mechanical alloying technique have been studied as negative electrode materials for lithium-ion batteries. With optimized compositions and structure morphologies, both Ag 52 Sn 48 and Ag 46 Sn 54 composite electrodes exhibit an initial capacity of ϳ800 mAh/g and maintain a reversible capacity of above 350 mAh/g for more than 50 cycles. Even after 300 cycles, the former still keeps a reversible capacity of approximately 200 mAh/g. Typically, the structural changes of Ag 52 Sn 48 electrode accompanied by Li insertion/extraction processes were examined by means of X-ray diffraction analyses. The results reveal that the composite alloy consisting of -Sn and Ag 3 Sn phases transforms mostly into that of ternary lithiated phase during Li insertion and recovers to one involving -Sn, Ag 3 Sn, and residual Ag 2 LiSn phases after Li extraction. It is considered that the composite structure containing the ternary lithiated phase, which is formed during the first cycle, is beneficial for the improvement of the cycle life of the Ag-Sn alloy electrode, although the residual lithiated product possibly leads to an increase of the irreversible loss.
The Ag-Fe-Sn alloy powders prepared by mechanical alloying technique have been studied as anode material for lithium-ion batteries. The half-cell tests with lithium counter electrode revealed that a suitable substitution of Fe for Ag led to a significant improvement of the cycling performance of the electrodes. Among these electrodes, the Ag 36.4 Fe 15.6 Sn 48 electrode was found to be capable of keeping a rechargeable capacity of about 280 mAh/g over 300 cycles, which was better than that of the Fe-free Ag 52 Sn 48 electrode. Typically, the structural changes of the Ag 26 Fe 26 Sn 48 electrode during Li insertion and/or extraction were characterized using the combined techniques involving X-ray diffraction, high resolution transmission electron microscopy, selected area electron diffraction, and energy dispersive X-ray spectrometry. It is considered that the electrochemical properties of these electrodes are associated with their microstructure and morphology, such as the distribution of intermetallic compound Ag 3 Sn in Sn matrix, the Ag 3 Sn/Sn ratio as well as the presence of inactive Fe.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.