Preparation Of Nano Silicon And The Silicon/Carbon Composites For Lithium Ion Battery

In recent years,lithium-ion batteries(LIBs)have been researched and applied widely by academia and industry because of the advantages of high energy,light weight,high voltage,low self-discharge rate,etc.,which arrows the relationship of people's life and LIBs.As one of the most important factors that determine the performances of commercial LIBs,the anode materials are mostly carbon-based materials currently,which have higher specific capacity,lower electrode potential,higher cycle efficiency and batter safety performance.However,with the increasing requirements of LIBs,carbon-based materials have been unable to satisfy people's demands.Silicon-based materials are favored because of their high specific capacity(theoretical specific capacity about 4200 mAh/g).But the poor electrical conductivity,huge expansion effect(greater than 300%)and the problem of pulverization cause the poor cycle stability of the silicon-based materials.Based on the above shortcomings,the commercial application of silicon materials is hampered.This thesis is intended to improve the electrochemical properties and achieve the commercialization of silicon materials mainly through preparing nano-silicon materials and combined with the carbon materials.Accordingly,the following several aspects were mainly studied:(1)The nano-silicon was prepared by ball milling.The optimal conditions for the preparation of uniform nano-silicon were obtained by optimizing the conditions such as time,speed,solvents,sizes of ball-beads and raw materials.The chemical properties of BmSi are improved compared to the raw materials.(2)BmSi/MWCNTs/C composites were prepared as anode material that used different methods and improved performance was obtained.The composites were prepared through ball milling and spray drying with BmSi,carbon nanotubes(MWCNTs),polyethylene glycol(PEG)and glucose(Glc)as raw materials.Characterized by SEM,Mapping and BET,it can be concluded that the materials are porous spherical composites with MWCNTs as the skeleton.The MWCNTs skeleton can form a conductive network to improve the conductivity of the materials and the porous structure provides sufficient space for the volume expansion of silicon,which are beneficial to improve the electrochemical performance.When applied as the anode materials of LIBs,the composite materials exhibit excellent cycle stability and superior rate performance.In this thesis,the preparation methods of whether the nano-silicon or the composite materials are simple,low-cost and suitable for high-volume production,which promotes to the application and commercialization of silicon-based materials in LIBs.