Carbon And Silver Decorated Silicon Particles For Lithium-ion Battery Anodes

With the rapid consumption of un-renewable energy, lithium-ion rechargeable batteries as a kind of environmental friendly energy have received a great deal of attention recently. Especially the dramatic development of the electric vehicles, leads a strong and ever-growing demand for high special capacity, good cyclability, safety, economical and friendly electrode materials instead of the traditional lead-acid batteries and nickel-hydrogen batteries. Whereas, at present, the conventional carbon materials of lithium-ion batteries anode electrode has a theoretical capacity limitation of 372mAh/g, which can not satisfied the demand for power systems with high energy and power densities. Thus, carbon is not the most promising anode material, researching for better anode materials is an ongoing pursuit.Silicon materials provide very high specific capacity (4200mAh/g) comparing with other alternative anode materials. However, the pulverization of the active materials followed by loss of electrical contact during the Li-insertion and extraction makes the cycle ability bad, limiting their large scale application. In order to improve the cyclability and rate capability of silicon material, developing methods have been studied. Among these, one of the most effectively method is making silicon-contained compound in nano-scale. Combining the advantages of nanosilicon grains such as high surface areas, small Li-insertion and extraction distance, short Li+ diffusion path, and slight polarization of the electrode during the charge and discharge in high rate with the synergistic effect in compound, achieve a superiority complementation by the all parts of the compound.In this thesis, we firstly introduce the principle of the Li-ion batteries, and then summarize the latest progress of new electrode materials. Our researches focus on the controllable growth of C@Si and Ag@Si compounds, and also on their electrochemical performance as anode materials for lithium-ion batteries. Meanwhile, all the samples were characterized by XRD, SEM, TEM, RAMAN and electrochemistry. The detail works as following:1. Fabricate the silicon particles by employing the high speed balling machine.2.Using prepared silicon grains and glucose as the start materials, synthesize the shell-core C@Si compound by combined solution-based chemical deposition and high-temperature decomposition (650℃in N2 protection) approach. This compound has been characterized by XRD, SEM, TEM, Raman. It is found that the sheet carbon covers uniformly on the Si paricles. Additionally, we have further analyzed the electrochemical performance for lithium-ion batteries. It exhibits an initial discharged capacity of 720mAh/g, the second discharge capacity is 300mAh/g, after 30 cycles, the discharge capacity still keeps 150mAh/g. Comparing with the pure silicon electrode, this C@Si compound electrode material displays a significantly improvement on the cycling performance. 3. Directly suppressing the work electrode by the prepared silicon grains, then immerse the electrode into the AgNO3 (0.005M)/HF (5M) solution, where the primary cell reaction occurs, leading the Ag particles homogeneously insert in silicon matrices. Finally, drying the sample at 50℃in the protection of N2. Further analysis to the Ag@Si compound, especially the time evolvement of the Ag particles in the compound, has been detailedly studied by the XRD, SEM, TEM. When serving as lithium-ion battery electrodes, the Ag@Si compound possesses capability of 440mAh/g at a rate of 150mA/g at first discharge, after 80 cycles the capacity retain 108mAh/g, which is significantly better than the pure silicon electrode.