Preparation And Modification Of Silicon/Carbon Anode For Lithium Ion Batteries

The development of anode materials with high specific capacity is of great importance for improving the energy density and battery life of lithium ion batteries.Silicon is considered to be the most potential anode material for the next-generation lithium-ion batteries due to its high theoretical capacity(4200 mAh g^-1),low operating voltage and abundant sources.However,silicon materials also show some disadvantages,such as large volume expansion（300%）,easy powdering and poor conductivity,thus resulting in the poor electrochemical stability and kinetic properties,which is difficult to meet the practical requirements.The electrochemical properties of silicon materials can be effectively improved by the compounding and nanocrystallizing.In this thesis,a simple ball-milling method and metal-induced chemical vapor deposition process were used to uniformly composite the carbon nanotubes（CNTs）with silicon,which can effectively alleviate the volume expansion of silicon anode and construct an efficient conductive network to improve its conductivity.The main contents of this thesis are as follows:（1）SCC-CNTs composite.Micron silicon and copper oxide were mechanically ball-milled,followed by chemical vapor deposition（CVD）to form the carbon nanotubes and amorphous carbon layers on the surface of silicon particles.The unique structure of SCC-CNTs composite consists of the conductive Cu₃Si,amorphous carbon layer,cross-linked CNTs,and the etched pores in Si matrix,which can play the synergistic effects on the electronic conductivity,Li⁺diffusion and volume expansion of Si anode during electrochemical process.The SCC-CNTs composites demonstrate the remarkably improved electrochemical performance compared with SiMPs,which can deliver a discharge capacity of 2171 mAh g^-1 at 0.4 A g^-1 with ICE of 85.2%,and retain 1197 mAh g^-1 after 150 cycles.（2）SFC-CNTs composite.The cheap ferrosilicon was used as raw material.Si/FeSi_x@C particles encapsulated in carbon nanotube networks（SFC-CNTs）were prepared by mechanical milling and chemical vapor deposition.Compared with ferrosilicon,the electrochemical properties of SFC-CNTs composite were significantly improved,which can deliver a discharge capacity of 1466 mAh g^-1 at 0.4 A g^-1 with ICE of78.2%,and retain 768 mAh g^-1 after 150 cycles.The research in this thesis shows that the combination of ball-milling,metal induced CVD,and etching method can successfully synthesize the Si-based composites with a hierarchical structure containing inner pores,surface carbon layer,and CNTs encapsulation.This structure can drastically enhance the electrochemical stability and kinetic performance,and the synthetic method is expected to be applied in the mass production of Si-based composites.