Study On Preparation And Property Of Silicon/Carbon Composite Anode Material For Lithium-ion Battery

The main goal of this paper is to improve the electrochemical performance of Si/C composite which is fabricated by using spray drying and pyrolysis technology. The effects of preparation technology and raw materials on the morphology and properties of Si/C composites have also been investigated. XRD, SEM, TEM and laser particle analyzer are performed to characterize the morphology and structure of composite. The charge/discharge test, cyclic voltammertry, alternating-current impedance test are used to get the electrochemical performance of Si/C composites.The paper concentrates on the optimazation of the technological parameters to prepare the Si/C composite with good electrochemical performance by spray drying and pyrolysis. The prepared Si/C composite exhibits an initial discharge specific capacity of 648.1 mAh/g with a coulombic efficiency of 77.2%. It exhibits good cyclic performance that maintains a discharge capacity of 528mAh/g after 30 cycles. By investigating the effects of different ball-milling time(lh,2h,3h,4h,5h), types and quantity of binder (lwt%,2wt%,4wt%,8wt%,16wt%), spray drying pressure(0.2MPa,0.25MPa,0.3MPa,0.35MPa), feeding rate(10rpm/min,25rpm/min, 50rpm/min), pyrolytic temperature(500℃,600℃,700℃,800℃)and carbon sources(10g,20g,30g,40g,50g)on the performance of prepared Si/C composites, the best technological parameters have been acquired. The details are as follows:ball milling 2h with dispersing agent, binder A of 8wt%,the spray drying pressure at 0.25Mpa,the feeding rate at 25rpm, the carbon source for 20g and pyrolytic at 600 V.By using good technological parameters, the different Si/C composite has been prepared on different graphite matrix. The main results are as follows:both the spherical graphite and expanded graphite can improve the initial capacity of lithium intercalation of Si/C composite in some degree. The Si/C composite with spherical graphite exhibits an initial discharge specific capacity of 888.3mAh/g with an initial coulombic efficiency of 75.4% and maintains a specific capacity of 371.3mAh/g after 50 cycles which is unstable. In contrast, the Si/C composite with expanded graphite exhibits an initial discharge specific capacity of 700.9mAh/g with an initial coulombic efficiency of 77.4%. This kind of composite got the excellent electronic conductivity and is adaptable to high rate capability.The asphalt as carbon source to prepare Si/C composite has been investigated. Comparing with the Si/C composite with carbon source of glucose, the prepared Si/C composite with carbon source of asphalt exhibits higher initial discharge specific capacity and charge specific capacity of 796.3mAh/g and 677.2mAh/g, respectively, and the initial coulombic efficiency could be reached 85.0%. The cyclic capability of this composite is more stable. Moreover, the morphology of the Si/C composite presents nearly-spherical, and the particles cohere with each other without any agglomeration.