| As the anode material of lithium ion batteries(LIBs),Fe3O4 has the advantages of higher theoretical capacity,natural abundant resources and low cost.At the same time,it has the disadvantage that the volume is easy to expand in the process of charge and discharge,resulting in structural collapse,which limits its industrial application.In order to make Fe3O4 as an ideal material for the anode electrode of the next generation lithium ion battery.In view of the above problems,this paper focuses the following research.(1)Effect of carbon source to alleviate the expansion of nano Fe3O4.In order to obtain N-doped carbon and improve the conductivity of carbon materials,aniline was used as synthetic raw material in this chapter.By adding 3wt%CNT of aniline monomer to the aniline oxidative polymerization system,the morphology of polyaniline was successfully adjusted to nanofibers(SF-PANI/CNT),and the carbonized materials with nanofiber morphology(SF-N-C/CNT)were obtained by further pyrolysis.Compared with carbon materials prepared by other methods,SF-N-C/CNT not only has N-doped structural carbon,but also contains uniformly dispersed CNT.Taking SF-N-C/CNT as lithium ion anode electrode,the reversible specific capacitance is 360 mAh g-1,the initial coulombic efficiency is 47.59%,the rate performance is excellent,and the capacity retention rate is as high as 95%after 500 cycles.As we all know,N-doped not only improves the conductivity of the material,but also introduces defects as an effective storage site of lithium ions,because N is electronegative and Li+is electropositivity.In addition,the defect is conducive to the diffusion of lithium ions into the internal space of the electrode material.(2)CNT and nano Fe3O4 form nanocomposites to improve the conductivity of nano Fe3O4,and asphalt is coated on the surface of CNT/Fe3O4 composite material as carbon source to further alleviate the expansion of nano Fe3O4.The results show that the CNT/Fe3O4@C composite electrode with a small amount(0.31%)of CNT has better cycle performance and high specific capacity at high rate than the C/Fe3O4 electrode.The CNT not only effectively improves the conductivity of nano Fe3O4,but also effectively inhibits the expansion of nano Fe3O4 as a mechanical support.Although the cycle and rate performance of CNT/Fe3O4@C composite electrode with high content(5.8%)CNT are improved,the specific capacity is not significantly improved compared with C/Fe3O4 electrode,because the aggregated CNT can not effectively alleviate the expansion of nano Fe3O4.The CNT/Fe3O4@C composite electrode with a small amount(0.31%)of CNT has better cycle performance(the specific discharge capacity is about 55 1.7 mAh g-1 after 300 cycles at 100 mA g-1 current density)and rate performance(the specific discharge capacity is 225 mAh g-1 at 1 A g-1).(3)According to the research results of the first two chapters,in this chapter,aniline is oxidized and polymerized on the surface of nano Fe3O4 to form core-shell type nmFe3O4@PANI,further pyrolysis into core-shell type nmFe3O4@C Nanocomposites.Taking micron Fe3O4 as a comparison,it is revealed that the construction of N-doped C layer on the surface of nano Fe3O4 can effectively improve the conductivity of nano Fe3O4 and inhibit the volume expansion of nano Fe3O4,and obtain very excellent cycle stability(the specific discharge capacity is about 340 mAh g-1 after 500 cycles at 100 mA g-1 current density)and rate performance(the specific discharge capacity is 160 mAh g-1 at 4 A g-1)However,N-doped C layer can not effectively improve the electrochemical properties of micron Fe3O4. |
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