Ionic liquid-induced ultrathin and uniform N-doped carbon-wrapped T-Nb₂O₅ microsphere anode for high-performance lithium-ion battery

Orthorhombic-phase Nb₂O₅ (T-Nb₂O₅) has been widely investigated as an intercalation anode material for Li-ion batteries due to the larger interplanar lattice spacing and high safety. However, its applications are limited by the intrinsic low electric conductivity. Herein, an ultrathin N-doped carbon-coating layer was constructed on porous T-Nb₂O₅ microspheres uniformly via a convenient thermal treatment method with ionic liquid as a carbon precursor. The synthesized T-Nb₂O₅@N–C exhibits significantly enhanced rate capability (155.5 mAh·g^–1 at 20C) than initial T-Nb₂O₅ (110.2 mAh·g^–1 at 20C). Besides, T-Nb₂O₅@N–C shows ultralong cycle life, with only a 0.02% decrease in the capacity per cycle at a high current density of 10C. The corresponding electrochemical tests show that the preferable rate capability of T-Nb₂O₅@N–C electrode is attributed to the increased electronic conductivity and pseudocapacitance contribution induced by ultrathin surface N-doped carbon layer. On the other hand, the mesoporous structure of T-Nb₂O₅@N–C ensures fast Li⁺ diffusion dynamics and electrolyte penetration. Furthermore, T-Nb₂O₅@N–C also performs well in a LiNi_0.5Mn_0.3Co_0.2O₄||T-Nb₂O₅@N–C full cell. This work provides a facile method to construct integrated anode materials for potential applications in lithium-ion batteries.