Phases Hybriding and Hierarchical Structuring of Mesoporous TiO2 Nanowire Bundles for High‐Rate and High‐Capacity Lithium Batteries

A hierarchical mesoporous TiO2 nanowire bundles (HM-TiO2-NB) superstructure with amorphous surface and straight nanochannels has been designed and synthesized through a templating method at a low temperature under acidic and wet conditions. The obtained HM-TiO2-NB superstructure demonstrates high reversible capacity, excellent cycling performance, and superior rate capability. Most importantly, a self-improving phenomenon of Li+ insertion capability based on two simultaneous effects, the crystallization of amorphous TiO2 and the formation of Li2Ti2O4 crystalline dots on the surface of TiO2 nanowires, has been clearly revealed through ex situ transmission electron microcopy (TEM), high-resolution transmission electron microscopy (HRTEM), X-ray diffraction (XRD), Raman, and X-ray photoelectron spectroscopy (XPS) techniques during the Li+ insertion process. When discharged for 100 cycles at 1 C, the HM-TiO2-NB exhibits a reversible capacity of 174 mA h g-1. Even when the current density is increased to 50 C, a very stable and extraordinarily high reversible capacity of 96 mA h g-1 can be delivered after 50 cycles. Compared to the previously reported results, both the lithium storage capacity and rate capability of our pure TiO2 material without any additives are among the highest values reported. The advanced electrochemical performance of these HM-TiO2-NB superstructures is the result of the synergistic effect of hybriding of amorphous and crystalline (anatase/rutile) phases and hierarchically structuring of TiO2 nanowire bundles. Our material could be a very promising anodic material for lithium-ion batteries.