Superior electrochemical properties of SiO2-doped Co3O4 hollow nanospheres obtained through nanoscale Kirkendall diffusion for lithium-ion batteries

Abstract

Hollow SiO2-doped Co3O4 (SiCo3O4) nanospheres with excellent Li-ion storage properties were synthesized via flame spray pyrolysis by applying a nanoscale Kirkendall diffusion process. A solid SiO2-doped CoO (filled SiCoO) nanopowder was prepared through this process, and then it was transformed into hollow SiCo3O4 nanopowder by way of a core-shell-structured CoSiO2 (filled Co@SiCoO) composite nanopowder. In addition, the direct oxidation of the filled SiCoO nanopowder at 300 °C under an air atmosphere resulted in the formation of a solid SiO2-doped Co3O4 (filled SiCo3O4) nanopowder. At a high current density of 2 A g−1, the hollow SiCo3O4 nanospheres exhibited a 150th-cycle discharge capacity of 971 mA h g−1 and capacity retention of 99.5%, which was measured relative to the second cycle. However, the corresponding capacity retentions of the filled SiCoO and SiCo3O4 nanopowders were only 82.2% and 71.5%, respectively. The high structural stability during cycling and high Li-ion conductivity, which are caused by the hollow structure, are responsible for the excellent Li-ion storage properties of the hollow SiCo3O4 nanospheres obtained through nanoscale Kirkendall diffusion.