Macaroni-Like Blue-Gray Nb₂O₅ Nanotubes for High-Reversible Lithium-Ion Storage

Due to the high reliability and high theoretical capacity, lithium-ion batteries (LIBs) have been widely studied in the world. Nevertheless, the existing LIB systems currently exhibit comparatively low capacities restricted by the anode materials. Herein, blue-gray Nb₂O₅ (B-Nb₂O₅) nanotubes are prepared which are rich in oxygen vacancy by a facile chemical vapor deposition (CVD) method and a further hydrogen annealing reduction as the anode material for LIBs, presenting a high discharge capacity of 375 mA h g⁻¹ at 100 mA g⁻¹ and a good rate performance up to 5 A g⁻¹ with 126 mA h g⁻¹. The detailed ex situ X-ray diffraction (XRD) and X-ray photoelectron spectra (XPS) characterizations verified the high-reversible process, which Li⁺ should insert into/extract from the (001) planes of Nb₂O₅ crystal. Combined with a reversible PF₆^- intercalation into/deintercalation from graphite cathode, a B-Nb₂O₅/graphite dual-ion cell can run about 50 cycles with the discharge capacity retention approaching 23 mA h g⁻¹ at 100 mA g⁻¹. The importance of the modulation of morphology and vacancy in improving overall electrochemical performance is highlighted.