Amorphous Tin Oxide Nanohelix Structure Based Electrode for Highly Reversible Na-Ion Batteries

An array of amorphous tin oxide (a-SnO_x) nanohelixes (NHs) was fabricated on copper foil as an electrode for Na-ion batteries via the oblique angle deposition method, a solution- and surfactant-free process. The combination of the amorphous phase SnO_x with a low oxidation number and its vertically aligned NH geometry with a large surface area and high porosity, which facilitate Na-ion dynamics and accommodate the volume changes, enabled a reversible capacity of up to 915 mA h g^-1 after 50 cycles, fast rate capability with 48.1% retention at 2 A g^-1, and high stability, which are superior to those of crystalline nanoparticle-based electrodes.