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Orthorhombic Nb2O5 (T-Nb2O5) nanocrystal@carbon hybrid spheres were synthesized via the controlled hydrolysis of niobium ethoxide, the assembly effect of oleylamine, and subsequent carbonization. The size of the T-Nb2O5 nanocrystals was ~ 26.6 nm, and the diameter of the hybrid spheres was 300–400 nm. The contents of T-Nb2O5 and carbon were 87.84% and 11.91%, respectively. The hybrid spheres exhibited excellent Li storage performance, including high reversible capacity (447 mAh g−1 at 0.5 A g−1/2.5C), good rate capability (186 mAh g−1 at 5 A g−1/25C), and excellent cycling stability (279 mAh g−1 after 600 cycles at 1 A g−1/5C). The capacity decay rate was only 0.06% per cycle. It has been found that the electrochemical performance of the hybrid spheres is superior to those of other reported Nb2O5 composites. Moreover, the reaction kinetics of the hybrid spheres are also outstanding. The impedance is low, while the Li+ diffusion coefficient is high. The hybrid spheres maintain good structural integrity after 600 cycles. The superior Li storage performance is associated with the unique architecture of the hybrid spheres. The ultrafine size of Nb2O5 nanocrystals ensures high electrochemical activity. The surface carbon and internal carbon of the hybrid spheres not only protect Nb2O5 but also promote the rapid transfer of electrons and Li+. These results demonstrate that T-Nb2O5 nanocrystal@carbon hybrid spheres are a promising candidate material for lithium-ion storage. [ABSTRACT FROM AUTHOR]

A composite of Fe3O4 and carbon is constructed by a one-step calcination method with polystyrene spheres as template, polyvinyl pyrrolidone as assembling agent, and Fe(NO3)3 as Fe source. Material characterization demonstrates that Fe3O4 hollow nanospheres 10–16 nm in diameter are closely grown in situ inside three-dimensional honeycomb macroporous carbon with a pore diameter of about 200 nm. The composite material exhibits high specific capacity, delivering an average discharge capacity of 1618 mA h g−1 at 0.1 A g−1. The long-term cycling performance is excellent, achieving discharge capacity of 770 mA h g−1 at 1 A g−1 after 1000 cycles and 429 mA h g−1 at 5 A g−1 after 200 cycles. Even at 10 A g−1, the rate capability is outstanding. Kinetics analyses reveal predominant capacitive behavior and low reaction impedance in electrochemical reaction. The excellent performance mainly benefits from the beneficial structural effects of Fe3O4 hollow nanospheres and honeycomb macroporous carbon. Fe3O4 hollow nanospheres@three-dimensional honeycomb macroporous carbon is a superior anode material for lithium-ion batteries. [ABSTRACT FROM AUTHOR]