Investigation Of Si/C Multilayer Thin Films As Anode Materials For Lithium Ion Batteries

The clean energy such as solar energy and wind is considered as the next generation of the most useful energy in the furure. They have been world-widely used, while most of them had a drawback, that is, they can’t offer energy all the daytime; The energy storage as long as energy support in some other facilities in the wild is also a problem to be settled at hand. As a result, to find a energy storage device with high capacity is of great importance. On the other hand, devices with high energy density and high power density should also be developed to meet the demand of the development of the pure electric veicles.The lithium ion batteries (LIB)have advantages such as high working voltage, high specific energy, good cycling stability and low charge memory. And to improve the performance of the LIB, the cathode and anode materials should be firstly studied.Silicon, with its highest specific capacity of about4200mAhg-1, was consided as the most promising anode material that can be used in the next generation of LIB. Expecially in the field of high energy and high power density LIB. But the high volume expantion of about400%largely limite its practical use and the most efficient solution was nano-sized+buffer layers.The electrochemical test were performed with different thicknesses and the modulate periods of the multilayer thin films. The results indicated that the films tend to have an active period with a high film thickness and with a property modulate period, the multilayer thin films showed a good cycling performance. With a modulate period dsu:dc=25nm:5nm,the multilayer thin films showed a reversible capacity of as high as2000mAhg-1after200cycles.To further improve the electrochemical performance, some amount of titanium is introduced into the films by co-deposition of Ti and Si targets. The results prove that the cycling performance of silicon films and Si/C multilayer thin films greatly improved compared with the films without Ti. The introduction of Ti element improved the diffusion of Li+and the activation of materials, thus improving the cycling performance.especially in the first few cycles.In summary, the thesis successfully improved the multilayer structure can accommodate the volume expansion of silicon and improve the cycling stability. Also the introduction of Ti can also help improve the cycling performance of both silicon films and multilayer thin films.The results indicated a promising future for the commercial use of silicon-based materials as the anode for lithium ion batteries.