Facile template-free preparation of hierarchical TiO2 hollow microspheres assembled by nanocrystals and their superior cycling performance as anode materials for lithium-ion batteries

The design and fabrication of hierarchical TiO2 hollow structures assembled by nanosized building blocks have been proven to be an effective strategy for significantly improving the electrochemical performance of TiO2-based anodes for lithium-ion batteries, which can be attributed to the increased surface lithium storage. Herein, uniformly distributed hierarchical anatase TiO2 hollow microspheres assembled by nanocrystals with an average size of 10-20 nm (denoted as TiO2 HMs) have been successfully prepared via a facile template-free one-pot hydrothermal process. The possible formation mechanism of TiO2 HM is also investigated by time-dependent and ammonium fluoride (NH4F) concentration-dependent experiments. Moreover, our strategy is simpler than other generally template-involved methods as it effectively avoids the tedious preparation and removal process of templates, and the time-consuming heating treatment for crystallization. As a promising anode material for lithium-ion batteries, TiO2 HMs exhibit excellent electrochemical performances in terms of high capacity, ultra-long cycling stability and good rate capability. After 1000 cycles, a capacity of 150.7, 129.9 and 104.5 mA h g(-1) is retained at 1, 5 and even 20 C, respectively. The peculiarly hierarchical hollow structure should be responsible for the excellent performances.