Design and synthesis of metal oxide hollow nanopowders for lithium-ion batteries by combining nanoscale Kirkendall diffusion and flame spray pyrolysis

This study introduces an efficient process that combines a gas phase reaction method and nanoscale Kirkendall diffusion for the large-scale production of metal-oxide hollow nanopowders. Core-shell-structured NiO@SiO₂ nanopowders prepared by flame spray pyrolysis are transformed into hollow NiO@SiO₂ nanopowders via a nanoscale Kirkendall diffusion process. The SiO₂ coating layer plays a key role in preventing the sintering and growth of the Ni or NiO nanopowders during the preparation process. The mean size of hollow core and shell thickness of the hollow NiO nanopowders are 11 and 7 nm, respectively. At a current density of 0.5 A g^-1, the NiO@SiO₂ nanopowders with hollow and filled structures exhibit 100th cycle discharge capacities of 885 and 338 mA h g^-1, respectively. In addition, the hollow NiO@SiO₂ nanopowders, which exhibit low charge transfer resistances and fast Li-ion diffusion rates, also show better cycling and rate performance than the nanopowders with filled structures.