| Lithium-ion batteries?LIBs?are gradually applied to electric vehicles and other large-scale energy storage equipments due to their high energy density,long lifespan.As the commercial LIBs anode material,graphite has a relatively low theoretical discharge capacity of 372 mAh/g,and can't satisfy people's needs.SiO2 anode material has the advantages of high theoretical specific capacity,low discharge platform,abundant and low cost,which has aroused widespread concern.However,SiO2 anode material has poor conductivity and larger volume expansion during charging and discharging,which seriously affects its cycle and rate performance.Hence,measures should be taken to solve these problems.In this paper,the design,synthesis and modification of the materials are mainly focused on improving the conductivity and the volume expansion effect of silicon anode materials.The SiO2/C composite materials were prepared by electrospinning,and the method has the advantages of simple process,low cost and environment friendly.In addition,a series of modification studies were carried out.After modification,SiO2/C/Cu?SiO2/C/CNTs?SiO2/C/rGO were prepared.The materials were characterized systematically by means of X ray diffraction?XRD?,scanning electron microscopy?SEM?,thermogravimetric analysis?TG?,charge and discharge test,electrochemical impedance?EIS?,cyclic voltammetry?CV?.The main contents of the research are as follows:?1?SiO2/PAN precursor was prepared by electrospinning with nano silica?SiO2?as raw materials and polyacrylonitrile?PAN?as carbon source.,and SiO2/C composite materials were obtained by pre oxidation and subsequent carbonization treatment.Different SiO2 content and carbonization temperature were studied in this paper.Find out that 20wt%of SiO2 in the SiO2/PAN precursor and carbonization temperature in 700?were the best conditions.At the current density of 100mA/g,the initial charge capacity of SiO2/C composite materials is 776.2mAh/g,after 100 cycles,the charge specific capacity still remains 480.5mAh/g.It is significantly improved compared to pure SiO2.?2?SiO2/C/Cu composite materials were prepared by electrospinning with Cu?CH3COOH?2·2H2O as copper source,and the content of Cu?CH3COOH?2·2H2O was optimized.When the content of Cu?CH3COOH?2·2H2O was 10wt%,SiO2/C/Cu composite materials maintain good morphology and exhibit the best electrochemical performance.At the current density of 100 mA/g,the initial charge capacity is 774 mAh/g;after 100 cycles,the charge capacity is 540.1 mAh/g.Compared to SiO2/C composite materials,the properties of SiO2/C/Cu composites have been improved.?3?SiO2/C/CNTs composites were prepared by adding different proportions of carbon nanotubes,using SiO2/C composites prepared by electrospinning as precursors.When the content of carbon nanotubes is 15wt%,the composite exhibits the best electrochemical performance.At the current density of 100 mA/g,the initial charge capacity is 811.4 mAh/g;after 100 cycles,the capacity retention as high as 74.23%.Compared to SiO2/C composites,the performance has been significantly improved.?4?Silica/carbon/graphene?SiO2/C/rGO?composites were prepared by adding different proportions of graphene oxide?GO?,using SiO2/C composites prepared by electrospinning as precursors.The graphene has the advantages of large specific surface area and good electrical conductivity,thus can suppress the volume expansion and improve the conductivity of the material.When the mass ratio of SiO2/C:GO is 4:3,the material exhibits the best electrochemical performance:the initial charge capacity is 891.6 mAh/g;after 100 cycles,the charge capacity is 648.5 mAh/g.At the current density of 100 mA/g?200 mA/g?300 mA/g?500 mA/g?1000 mA/g?1500 mA/g,the charge capacity are 837.85mAh/g?668.76 mAh/g?601.76 mAh/g?551.29 mAh/g?491.04 mAh/g?457.6 mAh/g,respectively.When the current density returns to 100 mA/g,the charge capacity can return to 662.92 mAh/g,and the rate performance is good. |
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