Porous TiNb2O7 nanofibers decorated with conductive Ti1−xNbxN bumps as a high power anode material for Li-ion batteries

Abstract

Titanium niobium oxide (TiNb₂O₇) has been reported recently as an attractive anode material for lithium ion batteries due to its practical capacity of ∼280 mA h g⁻¹, which is much higher than those of well-known metal oxide materials such as TiO₂ and Li₄Ti₅O₁₂. However, low electronic conductivity and poor lithium diffusivity limit its practical use as the active material in lithium ion batteries. Here, we synthesized porous TiNb₂O₇ nanofibers decorated with Ti_1−xNb_xN bumps via electro-spinning and thermal ammonia gas treatment. As-prepared nanofibers have one-dimensional geometry with an average diameter of ∼110 nm, and consist of ∼70 nm crystallites and pores in the range of 0–40 nm, shortening pathways for Li⁺ ion migration into the host material. Furthermore, conductive Ti_1−xNb_xN bumps with a particle size of ∼5 nm were formed on the surface via thermal ammonia gas treatment which render fast electron transport along the longitudinal direction. The fibers have a specific discharge capacity of ∼254 mA h g⁻¹ at 1 C and a superior rate capability (∼183 mA h g⁻¹ at 100 C). They also show a robust cycle performance over 500 cycles. These dramatic achievements are attributed to heterogeneous nano-structuring creating a porous structure, and the conductivity of the metal nitride achieved by optimal synthetic conditions.