Surface Nitriding Enables Improved Intercalation Pseudocapacitance of T−Nb2O5 for Lithium‐Ion Batteries

This paper presents large-grain nitrogen-doped T−Nb₂O₅ nanowires aimed at augmenting electrical conductivity and eliciting a pseudo-capacitance mechanism. The N−T−Nb2O5 nanowires exhibit exceptional electrochemical performance, manifesting an initial reversible specific capacity of 238.33 mAh g⁻¹ at 0.1 C. Furthermore, at a high rate of 100 C, there is a correlation between the degree of nitride incorporation in T−Nb₂O₅ and enhanced rate capability.

Abstract

The low electrical conductivity limits the application of T−Nb₂O₅ as anode materials for practical applications. The large-grain T−Nb₂O₅ nanowires with nitrogen doping are obtained by simple hydrothermal and annealing treatments. After nitriding with ammonia, an amorphous layer of NbON as an intermediate is formed and then the new crystalline NbN is generated with the deepening of the nitriding degree, causing homogeneous pores on the surface of the T−Nb₂O₅ and thus increasing the specific surface area. Meanwhile, the formation of the nitriding layer enhances the electrical conductivity, inducing a pseudo-capacitance mechanism. Therefore, the N−T−Nb₂O₅ nanowire demonstrates superior electrochemical performance. Specifically, the 45N−T−Nb₂O₅ nanowires delivered a first reversible specific capacity of 238.33 mAh g⁻¹ at 0.1 C, higher than of theoretical capacity (201.6 mAh g⁻¹). However, the excessive nitride will be completely converted into NbN, reducing the initial lithium storage of the material due to the lack of a lithium storage site, which has not been previously discussed. Besides, at the high rate of 100 C, with the deepening of nitride degree of the T−Nb₂O₅, the higher the rate performance. Therefore, to find the balance between the high rate performance and the initial lithium storage amount, the nitride degree should be strictly controlled.

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