Nanofibers Comprising Yolk-Shell Sn@void@SnO/SnO2 and Hollow SnO/SnO2 and SnO2 Nanospheres via the Kirkendall Diffusion Effect and Their Electrochemical Properties

Nanofibers with a unique structure comprising Sn@void@SnO/SnO2 yolk-shell nanospheres and hollow SnO/SnO2 and SnO2 nanospheres are prepared by applying the nanoscale Kirkendall diffusion process in conventional electrospinning process. Under a reducing atmosphere, post-treatment of tin 2-ethylhexanoate-polyvinylpyrrolidone electrospun nanofibers produce carbon nanofibers with embedded spherical Sn nanopowders. The Sn nanopowders are linearly aligned along the carbon nanofiber axis without aggregation of the nanopowders. Under an air atmosphere, oxidation of the Sn-C composite nanofibers produce nanofibers comprising Sn@void@SnO/SnO2 yolk-shell nanospheres and hollow SnO/SnO2 and SnO2 nanospheres, depending on the post-treatment temperature. The mean sizes of the hollow nanospheres embedded within tin oxide nanofibers post-treated at 500 degrees C and 600 degrees C are 146 and 117 nm, respectively. For the 250th cycle, the discharge capacities of the nanofibers prepared by the nanoscale Kirkendall diffusion process post-treated at 400 degrees C, 500 degrees C, and 600 degrees C at a high current density of 2 A g(-1) are 663, 630, and 567 mA h g(-1), respectively. The corresponding capacity retentions are 77%, 84%, and 78%, as calculated from the second cycle. The nanofi bers prepared by applying the nanoscale Kirkendall diffusion process exhibit superior electrochemical properties compared with those of the porous-structured SnO2 nanofibers prepared by the conventional post-treatment process.