Surfactant-free scalable synthesis of hierarchically spherical Co3O4 superstructures and their enhanced lithium-ion storage performances

Unique hierarchically porous spherical Co3O4 superstructures were synthesized via a surfactant-free hydrothermal process followed by a calcination treatment, in which the concentration of reactant cobalt (II) nitrate hexahydrate is a key factor affecting the morphology of products. X-ray powder diffraction, electron microscopies (TEM and SEM), and thermogravimetric analysis were employed to investigate the formation of Co3O4 spherical superstructures. Our results suggest that they formed from numerous cubic Co3O4 nanocrystals via an oriented attachment mechanism. These superstructures exhibit a high specific capacity of 1750 mA h g(-1) after the first charge-discharge cycle, and the capacity retention remains at a constant of 1600 mA h g(-1) at 0.2 C after 50 cycles. The facile, scalable, energy-efficient and environmentally friendly nature of the presented approach renders it particularly attractive from a technological standpoint. In addition, this scalable and facile synthesis method could be extended to the preparation of other transition metal oxides with specific morphologies and surface textures.