Study On The Preparation And Electrochemical Properties Of Silicon-carbon Composite As Anode Material

Nowadays, lithium ion batteries are widely used in a variety of advanced technologies as promising new energy sources. To satisfy the requirements of further development, many researchers focus on developing new anode materials with higher energy density to replace graphite which is a contemporary commercial anode material with a low theoretical capacity of 372 m Ah/g. The silicon-carbon composite has been presented to be a desirable material for combining the merits of both Si-based material and carbon material. In the composite, the Si-based material provides a high energy density, the carbon material provides a stable structure, high conductivity and extra lithium storage space. In this paper, we developed the Si/C,SiO2/C nanostructured composites by using Si, SiO2 and PAN through electrospinning,subsequent stabilization and carbonization. The influences of different Si-based material and their different content on both the morphology and the electrochemical performance were also studied.The Si/C composite with 15 wt.% Si was prepared by nano Si and PAN. The nano Si can disperse uniformly in the 3D network structure of nanofibers. The composite shows a capacity of 627.6 mAh/g after 10 cycles at a current density of 50 m A/g, which is about 160 mAh/g larger than the capacity of pure PAN-based carbon.By analyzing the rate performance, we can know that nano Si can improve the capacity of the composite under low current density, but it will degrade the rate performance of the composite under high current density.A series of nanostructured SiO2/C composites containing different content of SiO2 nanoparticles were also prepared. It is found that the SiO2/C composite with 15wt% SiO2 to PAN has the real SiO2 content of 23.6 wt.%. At this proportion of SiO2 to PAN, the best structure distribution of SiO2 in the nanofibers is gained. The composite exhibits a large capacity of 658 mAh/g after 100 cycles at a current density of 50 mA/g and retains 356 mAh/g at 1000 m A/g, showing the best performance with high capacity, good rate capability and excellent cycling stability.A further study of the reaction mechanism and kinetics based on different SiO2 content was carried out in this study. In the parallel reactions between SiO2 and lithium ions, the smaller Si O2 particles tend to form the reversible Li2Si2O5 phase,while the larger SiO2 particles tend to form the irreversible Li4SiO4 phase. Thisindicates that when the SiO2 content increases, more SiO2 nanoparticles begin to agglomerate, the agglomeration enhances the generation rate of irreversible Li4SiO4 and enlarges the irreversible capacity.