Silicon and porous MWCNT composite as high capacity anode for lithium-ion batteries

A silicon/porous multi-walled carbon nanotubes composite was synthesized using a simple method. A mixture comprising silicon nanoparticles and multi-walled carbon nanotubes was prepared by a mini ball milling method followed by annealing at low temperature. The low-temperature annealing treatment allows the aggregation of silicon nanoparticles and propels them to adhere to the outer walls of carbon nanotubes without the formation of a SiO_x layer on Si nanoparticles. Mild oxidation occurring on the carbon tube walls provides additional surface defects. The obtained composite, which was studied as an anode for Li-ion batteries, exhibited excellent cyclability and superior rate capability compared with pristine silicon nanoparticles. The improved electrochemical performance of the composite can be attributed to the electrically conductive carbon tubes, easy access of the electrolyte ions into the porous nanotube walls, and mechanical support provided by the carbon matrix. As a result, the proposed composite can sustain high discharge capacities of 1,685 mAh g⁻¹ at 1C rate after 80 cycles and 913 mAh g⁻¹ at 5C rate after 100 cycles.