Synthesis of hollow cobalt oxide nanopowders by a salt-assisted spray pyrolysis process applying nanoscale Kirkendall diffusion and their electrochemical properties

A new concept for preparing hollow metal oxide nanopowders by salt-assisted spray pyrolysis applying nanoscale Kirkendall diffusion is introduced. The composite powders of metal oxide and indecomposable metal salt are prepared by spray pyrolysis. Post-treatment under a reducing atmosphere and subsequent washing using distilled water produce aggregation-free metal nanopowders. The metal nanopowders are then transformed into metal oxide hollow nanopowders by nanoscale Kirkendall diffusion. Co ₃ O ₄ hollow nanopowders are prepared as first target materials. A cobalt oxide-NaCl composite powder prepared by spray pyrolysis transforms into several Co ₃ O ₄ hollow nanopowders by several treatment processes. The discharge capacities of the Co ₃ O ₄ nanopowders with filled and hollow structures at a current density of 1 A g ^-1 for the 150th cycle are 605 and 775 mA h g ^-1 , respectively. The hollow structure formed by nanoscale Kirkendall diffusion improves the lithium-ion storage properties of Co ₃ O ₄ nanopowders.