Synthesis Of Si-based, Fe₂O₃Anode Material For Lithium Ion Battery

In order to address power and energy demands of mobiles electronics ansd electric cars, Li-ion technology is urgently being optimized by using alternative materials. Silicon, silicon compounds, and transitions metals anode has attracted considerable attention during the last few years; researchers focus on their preparation owing to their electrochemical performance activity, catalytic activity, and the diversity of their structures.Three new series of lithium ion batteries rechargeable anodes materials have been synthesized and are collected in the chapters2,3and4respectively. Composite anode material of nano-Silicon-dioxide-carbon-alginate and Fe2O3/C/PAN/G composite were prepared by ball milling respectively. All samples have been characterized by elemental analysis, emission scanning electron microscopy (SEM), transmission electron microscopy (TEM), and the structures of the composites prepared have been determined by X-ray diffraction analyses.In chapter2, the preparation of the silicon based composite and its electrochemical performance. Nano-silicon composite electrode was fabricated by casting slurry via nmp and water. Such structure of nano-silicon composite made via water it possess hight discharge capacity of2491mAh g-1at0.1C. the capacity retention was kept above1425mAh g-1for a few cycles. The electrode fabricated via nmp possess a high capacity of2075mAh g-1with capacity retention of600mAh g-1above50cycles and the electrode with pvdf and alginate exhibits1041mAh g-1. Single X-ray diffraction analysis shows that the composite has a layer structure. However, the volume changes during the charging and discharging process are also affecting the electrochemical performance of the composites materials.In chapter3, the Fe2O3/C/PAN/G composite and its electrochemical performance has been prepared via ball milling and heat treatment by using, polyacrylonitrile, and graphite as complex carbon source at room temperature. The coated materials are found to enhance the electrochemical conductivity during the charging and discharging process. The active material has been characterized by emission scanning electron microscopy (SEM), transmission electron microscopy (TEM) and X-ray diffraction. It exhibits a stable reversible capacity of630mAh g-1with a coulombic efficiency of75%in the first cycle at a constant current density of1000mA g-1. An important phenomenon is that the specific capacity increase up to1025mAh g-1after several cycles. The good electrochemical performance is attributed to the Fe2O3nanoparticles and the veritable coating layer of Sucrose-PAN-G in the active material. It is effective at buffering the drastic volume changes, stabilizing the host structure, and preventing the aggregation on the surface of the electrode. It overall maintains a good electrical conductivity of the electrode during the process insertion and extraction of lithium. The reduced capacity in the few cycles after the initial capacity could be attributed to insufficient contact between the electrolyte and the inner particles of the Fe2O3.In chapter4, a composite anode material of nano-Silicon-dioxide-carbon-alginate was prepared by ball milling. The morphology and electrochemical performance of the silicon-dioxide were investigated through using alginate by changing the content of the nano-SiO2. The cell shows a large polarization during the charge-discharge.The resultant samples were characterized by emission scanning electron microscopy, transmission electron microscopy and X-ray diffraction. The superior electrochemical properties are attributed to better buffering effect of matrix and better electrical contact between the matrix, and the silicon particles. However, the volume changes during the charging and discharging process are also affecting the electrochemical performance of the composites materials.