W₃Nb₁₄O₄₄ nanowires: Ultrastable lithium storage anode materials for advanced rechargeable batteries

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 Li₄Ti₅O₁₂ anodes unavoidably possess some problems, such as high safety risk or low energy density. In this work, W₃Nb₁₄O₄₄ nanowires are developed via facile electrospinning as an anode material for LIBs. The W₃Nb₁₄O₄₄ demonstrates higher capacity, better cycling stability, and better rate performance than Ti-based compounds, such as Li₄Ti₅O₁₂ and TiO₂. The average working voltage plateau of W₃Nb₁₄O₄₄ nanowires is similar to those of Li₄Ti₅O₁₂ (about 1.55 V) and TiO₂ (about 1.6 V), which makes it a promising alternative to the Ti-based anode materials. Furthermore, W₃Nb₁₄O₄₄ exhibits a relatively large theoretical capacity of 293.56 mA h g⁻¹ (W⁶⁺/W⁵⁺, Nb⁵⁺/Nb⁴⁺, and Nb⁴⁺/Nb³⁺). In particular, when cycled at 1000 mA g⁻¹, W₃Nb₁₄O₄₄ nanowires can still deliver an initial reversible capacity of 130.6 mAh g⁻¹, while the electrospun Li₄Ti₅O₁₂ nanofibers and TiO₂ 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 W₃Nb₁₄O₄₄ nanowires undergo a reversible electrochemical reaction. The total volume change during charge/discharge is about 5.9%. In addition, W₃Nb₁₄O₄₄ nanowires exhibit a large Li⁺ diffusion coefficient of up to 8.02 × 10^–13 cm² s⁻¹. Such prominent merits of W₃Nb₁₄O₄₄ nanowires make them more likely to replace Ti-based anode materials for LIBs. © 2018 Published by Elsevier B.V.