Facile formation of tetragonal-NbO microspheres for high-rate and stable lithium storage with high areal capacity.

Niobium pentoxide (NbO) has attracted great attention as an anode for lithium-ion battery, which is attributed to the high-rate and good stability performances. In this work, TT-, T-, M-, and H-NbO microspheres were synthesized by a facile one-step thermal oxidation method. Ion and electron transport properties of NbO with different phases were investigated by both electrochemical analyses and density functional theoretical calculations. Without nanostructuring and carbon modification, the tetragonal NbO (M-NbO) displays preferable rate capability (121 mAh g at 5 A g), enhanced reversible capacity (163 mAh g at 0.2 A g) and better cycling stability (82.3% capacity retention after 1000 cycles) when compared with TT-, T-, and H-NbO. Electrochemical analyses further reveal the diffusion-controlled Li intercalation kinetics and in-situ X-ray diffraction analysis indicates superior structural stability upon Li intercalation/deintercalation. Benefiting from the intrinsic fast ion/electron transport, a high areal capacity of 2.24 mAh cm is obtained even at an ultrahigh mass loading of 22.51 mg cm. This work can promote the development of NbO materials for high areal capacity and stable lithium storage towards practical applications.