A novel Silicon-Carbon Nanotubes (Si-CNTs) hybrid materials have been fabricated at different Si concentrations on Cu substrates by single step hot filament chemical vapor deposition (HFCVD). A mixture of Polymer and Si nanoparticles was used as the seeding source and Ni nanoparticles as catalysts. Micro Raman spectroscopy shows the characteristic peak for Si nanoparticles around 506 cm-1 similarly D and G peaks establish the presence of CNT.
These results were confirmed by scanning electron microscopy (SEM), transmission electron microscopy (TEM) electron energy loss spectroscopy (EELS), X-ray Diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). The hybrid materials consist of multiwall nanotubes of diameters in the range of 20-100 nm. Field Emission results shows a very low turn-on field which confirm the presence of a good electrical interface between the substrate and the CNTs, due to direct growth on Cu substrate, and between the Si coating and the CNTs. Si content in the Si/CNT was estimated using Thermo gravimetric analysis (TGA) and Inductive coupled plasma-optical emission spectrometry (ICP-OES) and it is found to be in the range of 14-22 wt.%.
Electrochemical room temperature testing using coin cell batteries show that the Si-CNTs electrodes can deliver an initial high discharge capacity of around 700 mAh/g and a reversible capacity of around 500 mAh/g over 550 cycles, which is higher than the theoretical capacity of graphite electrodes. The cyclic voltammetry studies show a pair of redox peaks corresponding to lithium insertion and extraction, respectively. They also indicate good reversibility over extensive cycling, representing a promising anode material for rechargeable lithium ion batteries with high energy density. The Si-CNT films on the Cu substrate after electrochemical cycling showed that very few cracks were formed after Li alloying/dealloying. This is attributed to the high volumetric expansion of the silicon. However, the cracked film still had strong adhesion with the Cu substrate and delamination was not present.