Ni, FeO Nanocrystal-Integrated Hollow (Solid) N-Doped Carbon Nanospheres: Preparation, Characterization and Electrochemical Properties
In this paper, temperature-dependent phase-pure monodisperse NiO nanocrystals were prepared by thermal decomposition approach, showing sphere-like shape and snowflake-like NiO arrays. Such hydrophobic NiO nanocrystals were converted into hydrophilic nickel oxide-sodium oleate-Pluronic P123 (NiO-SO-P123) micelles in aqueous solution. In-situ formed phenolic resin (PR) was successfully deposited on hydrophilic area of NiO-SO-P123 micelles via heterogeneous nucleation mechanism to form NiO-phenolic resin nanospheres (NiO-PRNSs) with uniform particle size. By adjusting the size and amount of NiO nanocrystals used, the diameter of obtained NiO-PRNSs can be effectively controlled from 185 to 103 nm and shows a narrow size distribution, revealing the effect of NiO nanocrystals on the reconstructed NiO-integrated micellar size. Meanwhile, the morphologies (ring buoy, semi-bowl, sphere) depended upon initial NiO amount. The carbonization of NiO-PRNSs produced Ni(0)-integrated hollow N-doped carbon nanospheres (Ni(0)-HNCNSs), which showed the conversion of NiO to Ni(0), the contraction of particle size, and the starting NiO amount-affected metallic Ni size and distribution. However, by using monodisperse and polyhedral FeO nanocrystals, the obtained FeO-free/-incompletely filled and -fully filled core-shell structured Fe-PRNSs showed a relatively uniform particle size except multiple FeO cores forming large FeO-PR nanospheres with same FeO size as initial. The carbonized FeO-HNCNSs still preserved pomegranate-like core-shell structure with uniform size and no change on size of FeO nanocrystals. Moreover, high-loaded Ni(0)-integrated hollow or solid N-doped carbon microspheres or flakes can be synthesized by one-pot method, but with a broad size range, showing a highly uniform Ni distribution with a small Ni size as 8.5 nm. Note that Ni(0)- and FeO-HNCNSs were first prepared according to our knowledge. Finally, low loaded Ni-, FeO-HNCNSs with uniform morphology and size were chosen as the representatives to investigate electrochemical properties for lithium-ion batteries (LIBs), showing excellent lithium storage properties and superior reversibility. This study provides a potential strategy for controlling size and morphology of metal-integrated carbon materials for adjustable electrochemical property.