Atomic-scale investigation on lithium storage mechanism in TiNb2O7,

Abstract

Titanium niobium oxide (TiNb₂O₇) with a monoclinic layered structure has been synthesized by a solid state reaction method as an anode candidate for Li-ion batteries. The TiNb₂O₇ electrode shows a lithium storage capacity of 281 mAh g⁻¹with an initial coulombic efficiency as high as 93% at a current density of 30 mA g⁻¹ (ca. 0.1C). The average lithium insertion voltage is about 1.64 V vs.Li/Li⁺ at a voltage range of 0.8–3.0 V. The electrodes exhibit small voltage hysteresis (c.a. 0.1 V at 30 mA g⁻¹) and good capacity retention. Such superior electrochemical performance of TiNb₂O₇ makes it one of the most promising anode materials to replace spinel Li₄Ti₅O₁₂ for applications in hybrid vehicles and large scale stationary Li-ion batteries. In addition, we demonstrate crystal structures of TiNb₂O₇ and lithiated TiNb₂O₇ using advanced spherical-aberration-corrected scanning transmission electron microscopy (STEM), to picture the lattice sites occupied by the Li, Ti, Nb and O atoms at atomic-scale. Possible lithiation/delithiation processes and reaction mechanisms are revealed in consistence with first-principles prediction.