Oxygen vacancies enhance the lithium ion intercalation pseudocapacitive properties of orthorhombic niobium pentoxide.

ABSTRACT

While orthorhombic niobium pentoxide (T-Nb2O5) is one of the most promising energy storage material with rapid lithium ion (Li+) intercalation pseudocapacitive response, a key challenge remains the achievement of high-rate charge-transfer reaction when fabricated into thick electrodes. Herein, we report a facile method to create intrinsic defects in T-Nb2O5 through a hydrogen (H2) reduction, which is effective to overcome the limitations of electrochemical utilization and rate capability. Due to the high number of active sites introduced, the specific capacity of hydrogenated (H-) Nb2O5 with oxygen vacancies reaches 649 C g-1 at 0.5 A g-1, greatly exceeding that of T-Nb2O5 which is 580 C g-1. In addition, theformation of oxygen vacancies leads to increased donor density and enhanced electrical conductivity, which accelerates charge storage kinetics and enables excellent long-term cycling stability (86% retention after 2000 cycles). The analysis of electrochemical impedance spectroscopy (EIS) plots and the calculation of Li+ diffusion coefficients (DLi) further explains the high rate-performance of H-Nb2O5. When the electrode thickness increased to 150 µm, the H-Nb2O5 still delivers excellent electrochemical properties. Therefore, the introduction of oxygen vacancies provides a new method towards the improvement of the electrochemical properties of various transition metal oxides.