Doping sites modulation of T-Nb2O5 to achieve ultrafast lithium storage

Abstract

Heteroatoms doping has been regarded as a promising route to modulate the physiochemical properties of electrode materials, in which the doping sites greatly influence the electrochemical performances. However, very few reports focus on enhancing the lithium storage performances of Nb2O5 via heteroatoms doping, yet the effect of different doping sites remains unclear. Herein, nitrogen doping has been proposed to improve the fast-charging capability of orthorhombic Nb2O5 (T-Nb2O5) via a urea-assisted annealing process. Experimental data and theoretical calculation demonstrate that the N doping sites in T-Nb2O5 can be tuned by the heating rate, in which substitutional N can increase the spacing of the Li+ transport layer as well as reduce the band gap, while interstitial N can provide an electron-rich environment for Li+ transport layer and then reduce the Li+ diffusion barrier. Arising from the synergistic effect of N doping at different sites, the N-doped T-Nb2O5 without carbon coating delivers impressive rate performance (104.6 mA h g−1 at 25 C) as well as enhanced cycle stability with a retention of 70.5% over 1000 cycles at 5 C. In addition, the assembled lithium ion capacitor exhibits a high energy density of 46.6 Wh kg−1 even at high power density of 8.4 kW kg−1.