Al-doped Nb2O5/carbon micro-particles anodes for high rate lithium-ion batteries

Orthorhombic niobium pentoxide (T-Nb2O5) has attracted extensive attention in the field of ultra-fast lithium ion batteries (LIBs) due to its high rate performance. However, its instability at a low potential and inherent low conductivity limits its fast charging capability. Here, microspheres of aluminum-doped T-Nb2O5 embedded in N-doped carbon network (Al-Nb2O5@NC) are prepared. The effects of Al-doping on the crystal structure and electrochemical properties are systematically studied. It is found that Al-doping has led to increase of the density of O2− vacancies and low-oxidized state Nb4+ ions, improving ionic and electrical conductivity. The substitution of Al3+ ions for Nb5+ions improves the lattice stability, reduces the undesirable migration of Nb in cycling, and stabilizes the capacity during fast charging. The LIBs using Al-Nb2O5@NC as anode have high rate performance and cycling stability (i.e., ∼82 mAh g−1 at 20 A g−1 after 9900 cycles). Meanwhile, the intercalation-type electrochemical reaction is verified by in-situ transmission electron microscope (TEM), by which it is found that Al-Nb2O5@NC has better crystalline integrity. By integrating Al doping and carbon network, the micron-size Al-Nb2O5@NC particles developed in this work are promising anodes to build fast charge/discharge LIBs with high specific capacity, stability and excellent rate performance.