Preparation And Electrochemical Properties Of Si/C Composite Anodes For Lithium Ion Battery

Currently, graphite materials are the main anode materials for commercial lithium-ion battery. However, the limited theoretical capacity of 372 mAh/g. restrict its practical application in lithium-ion battery, due to the increased demands for energy storage device. Silicon is one of the most promising and attractive anode electrode material due to its low discharge potential and the highest theoretical charge capacity of 4200 mAh/g.Nevertheless, silicon anodes have been limited because of the low conductivity and the huge volume change during the lithium alloying-dealloying process. The huge volume change can cause pulverization and failure of the anode, which leads to a reduction in the capacity of the battery. To fabricate the Si/C composites would be an effective way to improve electrochemical properties of the Si-based anode of lithium-ion battery.In this paper, micro-sized and nano-sized silicon powders were used as the silicon source, while phenolic resin as the carbon source, the Si/C composites were prepared by a pyrolysis method and confirmed by means of transmission electron microscopy (TEM), scanning electron microscope (SEM) and X-ray diffraction (XRD). The preparations and the electrochemical properties of Si/C composite materials have been studied. The main results are as follows:(1) The Si/C micro-composite materials were prepared with micro-sized silicon powder as the Si source, and the carbonized temperature as well the Si contents were investigated. It is shown that the composite material is a dispersion of silicon particles within the carbon matrix. Compared with the electrode of pure silicon, this kind of Si/C composite material has a lower initial capacity, but a high cycle stability. As the carbonization temperature increases to 600℃, the silicon content becomes 26 wt.% with the best electrochemical performance. The first discharge capacities is 1171.9 mAh/g, and remains at 362.9 mAh/g after 40 cycles.(2) Two-dimensional (2D) ultrathin Silicon nanosheets (Si NSs) were synthesized by DC arc discharge method and used as the Si source for the Si/C nanocomposite materials, meanwhile, phenolic resin was used as the carbon source. The prepration of such nanocomposites as well the content of silicon have been investigated. It is shown that the nanocomposite has the structure with dispersion the silicon nanosheets in carbon matrix. These Si/C nanocomposite material have a lower initial capacity and an improved cycle stability. The best electrochemical performance can be obtained as the silicon content is of 31 wt.%. The first discharge capacity is 1090.5 mAh/g, and remains at 580.5 mAh/g after 100 cycles. In comparison with the counterpart of Si/C micro-composite electrode with the same content of silicon, such a Si/C nanocomposite electrode is obviously superior in the electrochemical performances.