| Silicon materials are attractive candidates for the next generation of lithium-ion batteries, due to their high theoretical specific capacity(4200 mAh g-1), a low intercalation/de-intercalation potential and low reactivity with electrolyte. However, the Si anodes have the poor cycling performance induced by the large volume expansion(~300%), leading to the particles crumbling and pulverization, eventually resulting in electrical deactivation and capacity fading, which occurs during Li-ions insertion/extraction. In addition, silicon’s low electrical conductivity also limits its rate performance. This has seriously affected the practical implementation of silicon anodes. In this paper, phenolic resin as the carbon source and silicon nanoparticles as the silicon source, are used to prepare the silicon/carbon nanocomposites and their structure and electrochemical performance are deeply investigated.(1) In this work, we synthesized a Si/SWCNT/OMC hybrid nanocomposite synthesized by the evaporation-induced self-assembly process. To investigate the effect of weight percentage of Si on the electrochemical cycle performance, three electrodes with different weight percentage of silicon have been prepared by adding different amount of Si suspension, respectively. The structure, the morphology and the electrochemical performance of the materials were investigated by scanning electron microscope(SEM), Transmission Electron Microscope(TEM), electrochemical tests, Brunauer-Emmett-Teller(BET), Thermogravimetric Analysis(TGA), X-ray diffraction(XRD), cyclic voltammetry(CV) and electrochemical impedance spectroscopy(EIS). The results showed that, at a current density of 400 mA g-1, it was clearly found that sample with Si weight percentage of 41 wt.% showed much higher lithium storage capacity than silicon weight percentage of 17 wt.% and 58 wt.%. The Si-0.41/SWCNT/OMC maintained a capacity up to 848.7 mAh g-1 after 50 cycles at a current density of 400 mA g-1, the initial discharge capacity was up to 1741.6 mAh g-1, and the initial coulombic efficiency was 70.8%. The single-walled carbon nanotubes(SWCNTs) have high electrical conductivity and flexible properties and are easy to prepare, making them suitable for constructing network to accommodate the expansion of Si-based anodes. The ordered mesoporous carbon and SWCNTs matrix could effectively accommodate the volume change of silicon nanoparticles, minimize the direct exposure of Si and maintain the integrity of the Si electrode. In addition, the ordered mesoporous structure could provide efficient channels for the fast transport of Li-ions.(2) In this work, we prepared siliocn/carbon/copper foam(Si/C/Cu) material as binder-free anodes for lithium ion batteries. The electrode material was characterized by SEM, TEM, XRD, TGA, and other analytical testing methods to study the morphology and structural changes. The effect of the silicon content in the Si-0.55/C/Cu and Si-0.625/C/Cu composite on the specific capacity of the batteries had been studied. The results showed that the Si-0.55/C/Cu electrodes displayed an excellent electrochemical performance. At a current density of 100 mA g-1, the reversible discharge specific capacity was maintained to be 907 mAh g-1 after 50 charge and discharge cycles. Through testing different charge-discharge current density, the material maintained a discharge capacity of 470 mAh g-1 at a current density of 1000 mA g-1, which showed a good rate performance. The excellent electrochemical properties of this composite were mainly due to the porous structure of copper foam, which provided void space for volume expansion of the silicon, and the amorphous carbon layers could effectively sustain the stress generated during the volume expansion. |
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