Ultrathin W9Nb8O47 nanofibers modified with thermal NH3 for superior electrochemical energy storage

Advanced high-rate anode materials with low cost and high reaction kinetics are greatly desired for development of high-power lithium-ion batteries (LIBs). Here, for the first time, the facile electrospinning and thermal ammonia gas nitridation treatment are developed to prepare nitrided W9Nb8O47 ultrathin nanofibers. The unique morphology is composed of conductive metal nitride bumps (W9Nb8N22, ∼ 8 nm) decorated on the surface of W9Nb8O47 nanofibers (∼ 40 nm). The nanostructured conductive W9Nb8N22 bumps can effectively improve the Li+ diffusivity and electronic conductivity of W9Nb8O47 nanofibers. As a consequence, the nitrided W9Nb8O47 nanofibers display superior practical capacity of 238.4 mAh g−1, which outperforms those of Ti-based oxide materials such as TiO2 and Li4Ti5O12. It also possesses high initial Coulombic efficiency of 83%, good rate performance (146.8 mAh g−1 at 5 C) and eximious long-term cycling stability (keeping 78% of the initial reversible capacity at a high current rate of 5 C after 1000 cycles). This performance is proved to be much superior to those of most reported intercalation-type anode materials for LIBs. Moreover, in the light of in-situ XRD, ex-situ TEM and HRTEM results, the Li+ insertion/extraction mechanism of nitrided W9Nb8O47 nanofibers as anode material is studied in detail. This work perfectly confirms that the W9Nb8N22 bumps can serve as the functional conductive nanoparticles to improve the electrochemical properties of W9Nb8O47 electrode for high-performance energy storage application.