Orthorhombic-Nb2O5 Nanocrystal@carbon Hybrid Spheres as Anode Material for Enhanced Lithium-Ion Storage

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 similar to 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. [GRAPHICS] .