Study On Polymer Modified Coal Asphalt And It’s Application On C/Si Composite Anode Material

Lithium-ion batteries play an irreplaceable role in the field of new energy because of their excellent performance.Silicon is the material with the highest specific capacity(4200 mAh/g),but its direct application to the negative electrode will cause serious volume expansion(400%)in the material,resulting in rapid capacity degradation and poor cycle performance of the battery.A large number of examples show that silicon and other materials can effectively reduce the volume expansion of silicon and improve its cycle life.Silicon-carbon composite is the current research hotspot.In this paper,C/Si composites were prepared by modifying coal tar pitch,using modified coal tar pitch as carbon source and silicon composite.The main research work and results are as follows:1.Modification of asphaltIn the emulsion polymerization system,the influence of raw material dosage,emulsifier order and shear rate on the stability of emulsified asphalt was investigated.The results show that stable emulsified asphalt can not be obtained by adjusting the above parameters.Finally,it is concluded that the viscosity of coal tar pitch is too high to be modified by emulsification.In bulk polymerization system,the effects of redox agent dosage and type,reaction temperature,coal tar pitch dosage and monomer dosage ratio on monomer conversion were investigated.Finally,the optimum process of coal tar pitch modification was obtained: coal tar pitch: monomer = 2:1,styrene: acrylonitrile = 7:3,BPO 0.54%,imidazoline 3 and reaction temperature 50.2.Testing and Characterization FIR,TGA,SEM and XRD were analyzed and characterized for modified asphalt.The results show that the performance of the modified asphalt prepared by this project has been greatly improved.3.Fabrication of C/Si CompositesC/Si composites were prepared by using modified asphalt prepared from emulsion system as carbon source.The average first discharge specific capacity of the material is about 1600 mAh/g,the first Coulomb efficiency is about 75%,and the reversible capacity can be reduced to 1000 mAh/g after 16 cycles.C/Si composites were prepared by blending modified asphalt and silicon under bulk polymerization.The first discharge capacity of the material is 1750 mAh/g,250 mAh/g higher than that of the unmodified medium-temperature asphalt.The first Coulomb efficiency is about 80%.The reversible capacity of the material after 20 cycles is about 1250 mAh/g,250 mAh/g higher than that of the unmodified medium-temperature asphalt,and the Coulomb efficiency is over 99%.It shows high specific capacity and excellent cycle performance.