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.

Javier Palomino Garate

University of Puerto Rico

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