Defect-Concentration-Mediated T-Nb2O5 Anodes for Durable and Fast-Charging Li-Ion Batteries

Metastable orthorhombic niobium pentoxide (T-Nb2O5) is a promising anode to fulfill the requirements for high-rate Li-ion batteries (LIBs). Stoichiometric T-Nb2O5 is plagued by low electric conductivity and particle pulverization after repeated charge/discharge processes. In this work, oxygen vacancies are implanted into T-Nb2O5 particles via acid immersion of Nb2O5 center dot nH(2)O with the formation of Lewis acid sites. The multiple characterizations and simulations reveal the lengthening of Nb-O bonds, and the transformation from NbO7 pentagonal bipyramids and NbO6 tetragonal bipyramids in T-Nb2O5-x. The enrichment of oxygen vacancies endows T-Nb2O5-x with higher electric conductivity, better electrochemical kinetics, larger pseudocapacitive contribution. O-doped graphitic C3N4 is creatively proposed as a trace oxygen pump to repair excessive oxygen vacancies, and it also serves as a sacrifice template for Nb2O5-x growth to construct a porous and monolithic electrode network. Defect-modulated Nb2O5-x displays extraordinary cycling stability (164 mAh g(-1) at 5 C after 1100 cycles), high capacity retention (104 mAh g(-1)) at an ultrahigh rate (25 C), and large areal capacity (0.74 mAh cm(-2)) under high mass loading (4 mg cm(-2)). The practical prospect is proved by Nb2O5-x/LiNi0.8Co0.1Mn0.1O2 full cells with high average platform (2.12 V) and high specific capacity (229 mAh g(-1)). The oxygen-defect modulation strategy on oxide anodes provides an alternative solution to fast-charging and durable LIBs.