Silicon Nanotube Anode on Copper Foils for Li-Ion Batteries

We report a silicon anode for lithium-ion batteries consisting of a layer of 100% nanotubes directly bonded to copper foil. The process involved silicon deposition on a sacrificial zinc oxide nanorod film and removal of zinc oxide to produce a nanotube film directly on thin copper foils. The thickness of resulting films ranged from 9 to 20 μm with Si nanotubes having diameters of 200–400 nm and lengths of 2–10 μm. The films with thin-walled tubes, 5–20 nm, had a silicon loading of 0.3 mg·cm –2 and exhibited durability over 100 cycles starting at 1345 mAh·g –1 (after first charge irreversible cycle), with Coulombic efficiency >97%. Tubes with wall thicknesses >150 nm resulted in degraded performance. Results demonstrate that higher loading and durable performance of the Si anode on copper foils is possible with film thicknesses >10 μm, but with tubes having wall thicknesses <150 nm.