W3Nb14O44 Nanowires: Ultrastable Lithium Storage Anode Materials for Advanced Rechargeable Batteries

Abstract Lithium-ion batteries (LIBs) have been extensively explored to meet the needs of current energy applications; nevertheless, the development of high-performance anode materials is a bottleneck for LIBs advancement. Current commercial LIBs based on graphite or Li 4 Ti 5 O 12 anodes unavoidably possess some problems, such as high safety risk or low energy density. In this work, W 3 Nb 14 O 44 nanowires are developed via facile electrospinning as an anode material for LIBs. The W 3 Nb 14 O 44 demonstrates higher capacity, better cycling stability, and better rate performance than Ti-based compounds, such as Li 4 Ti 5 O 12 and TiO 2 . The average working voltage plateau of W 3 Nb 14 O 44 nanowires is similar to those of Li 4 Ti 5 O 12 (about 1.55 V) and TiO 2 (about 1.6 V), which makes it a promising alternative to the Ti-based anode materials. Furthermore, W 3 Nb 14 O 44 exhibits a relatively large theoretical capacity of 293.56 mA h g −1 (W 6+ /W 5+ , Nb 5+ /Nb 4+ , and Nb 4+ /Nb 3+ ). In particular, when cycled at 1000 mA g −1 , W 3 Nb 14 O 44 nanowires can still deliver an initial reversible capacity of 130.6 mAh g −1 , while the electrospun Li 4 Ti 5 O 12 nanofibers and TiO 2 nanofibers can only deliver an initial reversible capacity of 95 and 75 mAh g −1 , respectively. Furthermore, the in-situ X-ray diffraction, ex-situ X-ray photoelectron spectroscopy, and ex-situ transmission electron microscope results reveal that W 3 Nb 14 O 44 nanowires undergo a reversible electrochemical reaction. The total volume change during charge/discharge is about 5.9%. In addition, W 3 Nb 14 O 44 nanowires exhibit a large Li + diffusion coefficient of up to 8.02 × 10 –13 cm 2 s −1 . Such prominent merits of W 3 Nb 14 O 44 nanowires make them more likely to replace Ti-based anode materials for LIBs.