| Silicon has been regarded as one of the most promising next-generation lithium-ion batteries anode materials due to its ultrahigh theoretical specific capacity and low discharge potential. However, the large volume changes in silicon upon insertion and extraction of lithium-ions destroy the electrode materials, which to rapid capacity fading. Meanwhile silicon has poor electrical conductivity, which limits its commercial application. Nanostructured silicon or silicon combine with carbon materials can significantly reduce the volume effect of silicon-based materials. By taking advantages of good mechanical properties of SiO2 and good electrical conductivity of carbon materials, silicon/carbon anode materials with novel structure,controllable shape and good cycle performance were prepared through different methods.Nano-silicon particles coated a 10nm layer of SiO2 was prepared through the hydrolysis of tetraethyl orthosilicate, with different sized particles of nano-silicon as raw materials. Based on the prepared SiO2/Si materials, carbon/SiO2/Si composites were prepared with sucrose and RF resin as carbon sources respectively. It indicated that SiO2 and carbon double coated on silicon particles.SiO2 layer with strong mechanical properties limited the expansion degree of silicon during the lithiating process. Carbon layer can also provide the transmission channel for ions and electrons by its excellent conductivity, as well as a protective layer. The cycle stability of materials has been significantly improved because of the chemical inertness, porous structure and selective permeability of amorphous SiO2 and carbon.GNS/SiOx/Si composite was obtained by surface modifications, electrostatic self-assembly and thermal reduction, silicon particles with diametres between 30-50 nm were thoroughly wrapped in the graphene sheets and thus formed a three-dimensional structure. At 50 mA g-1, the initial reversible capacity of electrode materials was as high as 1050 mAh g-1, with the corresponding coulombic efficiency of 61.71%. After 30 cycles, the electrodes shows a high capacity of 1029 mAh g-1, with capacity retention of 98%, and the coulombic efficiency has been maintained more than 95%, showing obvious higher capacity and cycle stability than silicon raw materials.Basing on C/SiO2/Si composites, GNS/C/SiO2/Si was prepared by electrostatic self-assembly and thermal reduction, which showed a clear three-dimensional porous structure. Although the initial coulombic efficiency was decreased after graphene was added in the composites, the rate performance was significantly improved, and this is attributed to the good conductivity and the special fold structure of graphene, which has shortened the ion transport path, and has provided more transport channels for ions and electrons. |
