Highly [001]-oriented N-doped orthorhombic Nb ₂ O ₅ microflowers with intercalation pseudocapacitance for lithium-ion storage

Orthorhombic Nb₂O₅ (T-Nb₂O₅), a typical intercalation pseudocapacitor, is favorable for realizing high power and energy density for lithium-ion batteries; furthermore, the 2D layered channels perpendicular to the [001] direction facilitate fast Li⁺ intercalation in T-Nb₂O₅. Herein, N-doped T-Nb₂O₅ microflowers (N-Nb₂O₅) assembled from highly [001]-oriented nanoflakes are rationally synthesized using NH₄F as the nitrogen source and capping agent. It is found that NH₄⁺ can adsorb on the O-terminated (010) plane of T-Nb₂O₅via N-H⋯O hydrogen bonds, which is highly conducive to the generation of 1D nanorods and the subsequent fusion of the nanorods into highly [001]-oriented nanoflakes. The special growth orientation of the T-Nb₂O₅ nanoflakes endows them with abundant available Li⁺ intercalation channels; moreover, the bandgap of N-Nb₂O₅ is narrowed (∼2.91 eV) owing to the doping of N atoms, and the intrinsic electronic conductivity is improved. Accordingly, the intercalation pseudocapacitive behavior of N-Nb₂O₅ is notably promoted and N-Nb₂O₅ exhibits superior Li⁺ storage properties, including large discharge capacity (214.7 mA h g^-1 at 1C), excellent rate capability (203.7 and 174.6 mA h g^-1 at 1 and 20C), and superior cyclic stability (150.7 mA h g^-1 at 10C after 1000 cycles). In addition, the LiNi_0.5Mn_0.3Co_0.2O₂//N-Nb₂O₅ full cell delivers outstanding Li⁺ storage performance, especially in terms of long-term cycling (126.2 mA h g^-1 at 10C after 3500 cycles).