Electrochemical Studies Of Silicon And Silicon-carbon Film Electrodes Prepared In Lithium Ion Batteries

In the recent years, with the miniaturized development of microelectronic devices, miniaturized energy systems are urgently needed that adapt to them. The miniaturized power sources system that is applied extensively for the Micro Electro-Mechanical System (MSMC) is one key technology. Lithium ion battery is a promising one of the micro power sources because of excellent cyclic performance and storage energy. The researchers actively exploit and investigate the non-lithium anode film with low reaction activity presently in order to improve the properties and safety.Silicon which is an important non-lithium anode material has been paid much attention by the researchers in last years due to the highest theory insertion lithium capacity (4200mAh/g). But silicon as anode materials has a bad cyclic performance because its volume expands in the process of insertion lithium ion. By reducing silicon size with nanotechnology and thin film silicon, the high capacity, stable microstructure and electronic-contact may be improved. Simultaneously, the increase of conductivity may be expected by using silicon composite with carbon that has excellent ion and electronic conductivity and volume change rate.In this paper, amorphous silicon and silicon-carbon multilayer films deposited on Cu substrate were prepared by ion-beam sputtering. Its electrochemical performance was studied. That no obvious diffraction peaks of silicon have been found in XRD spectrums of silicon and silicon-carbon multilayer films demonstrates the amorphous states of silicon and carbon under our experiment conditions. The sputtering deposited film consists of micro particle with a size of a few micrometers, determined by the roughness of the surface of Cu foil substrate. Silicon and silicon-carbon multilayer films are prepared by controlling sputtering currents and different sputtering time. The results are that the silicon film with larger sputtering current and longer sputtering time shows a higher capacity and cyclic performance. Because the increase of deposition rate causes the decrease of short-range order. At the current density of 6.5μA cm^-2, the capacity retention of silicon can be 580mAh/g that is the best silicon film. The first coulombic efficiency of silicon film anode at the current density of 6.5μA cm^-2 is 80%, nearly 2%...