The Preparation Of Silicon/Carbon Anodes For Lithium Ion Batteries Derived From Coal Tar Pitch-Based Carbon Materials

Large-scale energy storage and the rapid development of the electric vehicle industry require lithium ion batteries with higher energy density and cycle stability.The low specific capacity of traditional graphite anode materials(372 m Ah g-1)severely restricts the improvement of energy density of lithium ion batteries.Silicon-based materials with high specific capacity(3600 m Ah g-1),abundant reserves,and low lithium insertion voltage are considered to be the most commercially promising next-generation lithium-ion batteries anode materials.However,the volume expansion of silicon-based materials during cycles is huge and the conductivity is poor.The huge volume expansion will cause the electrode structure to be destroyed and cause rapid degradation of its cycling performance.The carbon materials have a stable structure and good conductivity.Compounding silicon and carbon materials is one of the methods to effectively improve the performance of silicon anodes.Coal tar pitch has a wide range of sources,low cost,and high carbon yield.It is a high-quality carbon material precursor.The application of coal tar pitch-based carbon materials in the field of energy storage can realize the high value-added utilization of coal tar pitch.In this paper,the silicon-carbon materials were fabricated using coal tar pitch-based carbon material and silicon nanoparticles as raw materials,which realizes the low-cost and large-scale preparation of silicon-carbon materials.The research contents and results are as follows:Silicon/carbon composites were fabricated using coal tar pitch-based soft carbon,silicon nanoparticles(Si NPs)and chitosan as raw materials through ball milling and carbonization treatment.The Si NPs are embedded in the soft carbon sheets which can relieve the volume expansion of Si and increase the electronic conductivity of the composites.The chitosan-derived carbon which disperses in the composite connects the Si NPs with soft carbon sheets and increases the structural stability of the composites.In addition,after adding chitosan,the specific surface area of Si/MSC900/Ch-4 decreases and its initial coulomb efficiency increases.The initial coulomb efficiency of Si/MSC and Si/MSC900/Ch-4 are63.68% and 70.57% respectively.As the amount of chitosan added increases,the average carbon layer spacing and the degree of amorphous increase.In addition to adding the third component chitosan,changing the carbonization temperature of coal tar pitch during the preparation of soft carbon will also affect the microstructure and electrochemical performance of the composites.As the carbonization temperature of coal tar pitch increases,the degree of graphitization of the composites increases and the defects decrease.When the mass ratio of soft carbon to chitosan is 4: 1 and the carbonization temperature of coal tar pitch is 900?,the Si/MSC900/Ch-4 exhibits the excellent lithium storage performance.The initial reversible capacity of the composite is 690.6 m Ah g-1 at 0.1 A g-1.Even at 5 A g-1,the composite delivers capacity of 410 m Ah g-1.After 200 cycles at 1 A g-1,the composite achieves capacity of 386 m Ah g-1.The silicon-carbon composites were prepared by the process of liquid phase solidification and high temperature carbonization using coal tar pitch,silicon nanoparticles and PAN as raw materials.The carbon material can isolate the silicon nanoparticles and hinder the agglomeration of the silicon nanoparticles which can alleviating the volume expansion of silicon effectively.Coal tar pitch-derived carbon has a high degree of graphitization and good conductivity can promote the rapid transportation of electrons.The addition of PAN can hinder the graphitization trend of coal tar pitch during the carbonization process,increases the average carbon layer spacing and amorphous degree of the composites which can facilitate the transportation of lithium ions.Under the synergistic effect of coal pitch-derived carbon and PAN-derived carbon,Si/C/PAN-X series composites have excellent electrochemical properties.Under the current density of 2 A g-1 and 5 A g-1,the specific capacity of Si/C/PAN-2 can reach 466.7 m Ah g-1 and 392.6 m Ah g-1,respectively.After 100 cycles at 1 A g-1,the specific capacity of Si/C/PAN-1 is 423 m Ah g-1 and the capacity retention rate is 81%.