Preparation And Properties Of Carbon Coated Nano Silicon Composite Anode Materials

Lithium-ion batteries have many advantages,such as high specific capacity,good cycle stability,environmentally friendly,non-memory effect,higher safety factor and so on,therefore,lithium-ion batteries are preeminent among the numerous energy storage device and have been gained comprehensive attention.However,with the development of science and technology,the requirements of all kinds of portable electronics,electrodynamic instrument and military equipment are more and more strict with electrode materials.Lithium-ion battery which has high capacity,cycle stability and power is what researchers want to develop.Anode material is the key to production of lithium-ion battery.As one of new anode materials,silicon possess high specific capacity and has been a research hotspot.But there exists serious problem of volume expansion of silicon during the charge-discharge cycling process,which results in the sharp dropping in capacity and seriously hinder the commercialization of silicon anode.It is worth noting that the presence of carbon materials can make up for the defects.Carbonre materials have a number of advantages,for example,lower intercalation potential,capacity fading slowly,good cycle stability and not obvious volume change.If silicon and carbon materials are prepared to composite anode materials,the composite materials can take full advantage of both,in this way,the ideal anode material is expected to be prepared.In this study,ethyl cellulose is used as carbon source,and carbon coated nano silicon composite anode materials are obtained after hydrothermal carbonization,high temperature activation and HF etching SiO2,then the anode material is prepared to be electrode and assembled to be coin sized lithium ion battery.The effects of the reaction condition on the morphology and particle size distributions are investigated.The effects of activation temperature and silicon contents on the electrochemical performance of anode material are researched.Scanning electron microscope(SEM),X-ray photoelectron spectroscopy(XPS),Fourier transformed infrared spectra(FT-IR),X-ray diffraction(XRD)and laser particle size analysis are used to characterize and analyze the morphology,particle size distributions,functional groups distributions and crystal structures of samples.SEM and laser particle size analysis show that the spherical structure of obtained materials is smooth and regular,the average diameter is 7.2?m;FT-IR and XPS reveals that there are new functional groups such as carboxyl and aromatic ring appeared during hydrothermal carbonization process.The characteristic absorption peak of silicon and amorphous carbon could be obvious observed in the XRD graph.The electrochemical performance tests demonstrate that the initial discharge specific capacity of the sample is 930.3 mAh/g,and the initial coulombic efficiency is 69.1%,in addition,after 40 cycles,the capacity retention ratio of obtained lithium batteries is 64.7%.Polyacrylamide is prepared by reversed phase suspension polymerization using acrylamide as monomer.Nitrogen doped carbon coated nano silicon anode materials are synthesized using polyacrylamide as nitrogen and carbon source after high temperature activation and HF etching SiO2,then the sample is assembled to be coin sized lithium ion battery.The effects of amount of initiator and dispersant,oil-water ratio and shear speed on the synthesis of microspheres have been studied.SEM and laser particle size analysis indicate that the spherical structure of microspheres is good and the average diameter is 10.1?m;the FT-IR analysis reveal that acrylamide is easy to polymerization,and polyacrylamide could be easily prepared;it is obvious that the crystal structures of silicon unchanged after coating.The electrochemical performance tests demonstrate that theinitial discharge specific capacity of the sample is 1055.5mAh/g,and the initial coulombic efficiency is 71.8%,it is also worth noting that as the result of nitrogen doped,the capacity fading of anode material become slowly under high current density and the cycle stability improved.