Silicon Nanotube\nAnode on Copper Foils for Li-Ion\nBatteries

We report a silicon anode for lithium-ion batteries consisting\nof a layer of 100% nanotubes directly bonded to copper foil. The process\ninvolved silicon deposition on a sacrificial zinc oxide nanorod film\nand removal of zinc oxide to produce a nanotube film directly on thin\ncopper foils. The thickness of resulting films ranged from 9 to 20\nμm with Si nanotubes having diameters of 200–400 nm and\nlengths of 2–10 μm. The films with thin-walled tubes,\n5–20 nm, had a silicon loading of 0.3 mg·cm<sup>–2</sup> and exhibited durability over 100 cycles starting at 1345 mAh·g<sup>–1</sup> (after first charge irreversible cycle), with Coulombic\nefficiency >97%. Tubes with wall thicknesses >150 nm resulted\nin degraded\nperformance. Results demonstrate that higher loading and durable performance\nof the Si anode on copper foils is possible with film thicknesses\n>10 μm, but with tubes having wall thicknesses <150 nm.