Preparation And Electrochemical Properties Of Carbon-Silicon Composites

With the exhaustion of energy and resources in human society,the development and utilization of new energy has become the primary task of the people.Silicon-based anode electrode material has higher theoretical specific capacity.But in the actual application process,the inevitable volume expansion of Si will reduce the cycle stability performance of the battery.Carbon materials have good electrical conductivity.They can be used to buffer the expansion of silicon volume and enhance the electrical conductivity of negative electrode materials,which can guarantee a high specific capacity and improve the cyclic stability.In this study,silicon/carbon composite anode materials were prepared with different preparation methods by using polyaniline and acetylene gas as the carbon sources and nanoscale silicon as the silicon source.The structure and morphology of the samples were characterized by SEM,TEM,XRD and TGA.The electrochemical properties of the samples were tested.Specific research contents and results are as follows.?1?The polyaniline coated silicon nanocomposites were prepared by using nanocrystalline silicon and aniline as raw materials,and then the outer layer of polyaniline was carbonized to carbon by high temperature calcination.The effects of different carbon/silicon ratios on their electrochemical properties were discussed.Results show that the carbon layer coated on the surface of nanoscale silicon particles uniformly,and there was no other by-products formation during the pyrolysis process.The initial specific capacity of the commercial pure nano silicon powder was 2679mAh g^-1,while after 5cycles,its capacity reduced to less than 100mAh g^-1.In comparison,the cycling performance of the nanoscale silicon coated with polyaniline has been improved obviously.The electrochemical performance of SiPANI-30wt%composite was the best.The initial specific capacity was 904.2mAh g^-11 and maintained at 548.6mAh g^-11 after 200 cycles.?2?The yolk-shell Si@void@C composites were prepared by chemical vapor deposition and using nano silicon and acetylene as raw materials.The thickness of carbon coating was adjusted by controlling the carbonization time during CVD process.The electrochemical properties of the composites with different carbon and silicon ratios were investigated.Results show that the Si@void@C composite obtained via 15min carbonization presented the best performance.The initial specific capacity was 1048mAh g^-1and maintained at 983mAh g^-1after 200 cycles.The retention rate of capacity was 93%and the initial coulombic efficiency was 73%.Compared with the core-shell Si@C composites prepared under the same conditions(the initial specific capacity was 981mAh g^-1and maintained at 635mAh g^-1after 200 cycles,and the retention rate of capacity was65%)the yolk-shell Si@void@C composites presented a higher capacity and a better stability.The possible mechanism was discussed in this paper.