(333d) Silicon-Coated Carbon Nanotube Anodes for Lithium-Ion Batteries

Current rechargeable lithium-ion batteries contain anodes made of graphite. They are most often used for powering small devices such as cell phones and laptop computers, because they are cost-effective, have a sufficient theoretical reversible storage capacity (~372 mAh/g), and exhibit a long battery life. Although graphite anodes are adequate for powering these small devices, they don't possess enough theoretical storage capacity to power larger devices, such as hybrid electrical cars, the power grid, or components found in space craft. Silicon has a much higher theoretical reversible capacity (~4,200 mAh/g), which would provide rechargeable batteries the potential to store much more energy during charging. Silicon has been reported to store up to 22 lithium ions for every five silicon atoms, compared to graphite, which can store only one lithium ion for every six carbon atoms. The only challenge with using silicon based anodes lies in their resulting pulverized structure after repeated cycles of Li-ion charging and discharging, due to the extreme volume changes from the lithiated state during charging and the delithiated state after discharging. In this work, multi-walled carbon nanotubes were used as mechanical reinforcements for amorphous silicon, which supplied an effective method for creating functional, high storage capacity, rechargeable Li-ion batteries. The carbon nanotubes were grown via thermal chemical vapor deposition on an electropolished [100] copper foil. A 10 wt% solution of iron(III) p-toluenesulfunate in ethanol was spin casted on the copper substrates, serving as the catalyst. Finally, amorphous silicon was deposited on top of the carbon nanotubes using plasma enhanced chemical vapor deposition. The anodes were paired with a cathode and electrolyte, forming a full coin cell, and electrical impedance, current density, and charge/discharge rate measurements were collected.