| Si based materials are the most promising material because of its high theoretical capacity of 4200 mAh.g-1.However,the practical use of silicon in LIBs has been mainly hindered by its huge volume expansion（>300%）and low conductivity.Designing porous microstructure or compounding Si particles with other high conductive materials is an effective strategy to overcome these problems.SiO2/C composites were synthesized via carbonization of SiO2/RF aerogel precursor.The effects of drying method and carbonization temperature on electrochemical properties were investigated.The reversible capacity of SiO2/C retains480 mA h g-1 at 0.1 A g-11 for 100 cycles.The results reveal that the porous microstructure and improved temperature is helpful to the electrochemical properties of materials.However,the initial coulombic efficiency of SiO2/C is only about 30%,which can be ascribed to the irreversible reaction between the oxygen and lithium ions.A three-dimensional Si/G composite was synthesized via one-pot hydrothermal method and magnesiothermic reduction.The reversible capacity of Si/G retains 580 mA h g-1 at 0.1 A g-11 for 100 cycles.Compared to the bare Si,the Si/G composites show an improved cycle stabilization due to the incorporation of graphene.The initial coulombic efficiency of Si/G were significantly prompted to 70%,which is owing to the high-efficiency of magnesiothermic reduction.A hierarchically G/Si/C 3D porous composite was synthesized through spary drying,magnesiothermic reduction and CVD.The graphene skeleton can effecitively enhance the inner electricity and accommodate the volume changes of Si during cycling and provide a large interfacial reaction zone,while the carbon ensures the stability of the whole structure and further improve the electronic conductivity of the electrode.As a result,the G/Si/C electrode exhibits a reversible capacity over 1450 mA h g-1 at 0.1 A g-1 after 100 cycles and a capacity around 550 mA h g-11 at 10 A g-1. |
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