Template-free synthesis of homogeneous yolk–shell TiO2 hierarchical microspheres for high performance lithium ion batteries

The homogeneous yolk–shell TiO 2 hierarchical microspheres (TiO 2 HYSHMs) consisting of small nanoparticles have been fabricated through a facile template-free solvothermal reaction followed by calcination . The obtained samples were characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy , nitrogen adsorption/desorption analysis and Fourier transform infrared spectroscopy. It was found that the microspheres have porous shell (∼100 nm in thickness) composed of small nanoparticles with an average diameter of 10 nm. The interspace between the yolk and shell is ∼150 nm. The BET specific surface area and pore volume of the sample are 151.1 m 2  g −1 and 0.23 cm 3  g −1 , respectively. Ostwald ripening processes are proposed to explain the growth mechanism of the TiO 2 HYSHMs based on a series of time-dependent experiments. As the anode materials for the lithium ion batteries , TiO 2 HYSHMs exhibit a high initial discharge capacity of 267.6 mAh g −1 at 0.25 C and retain 191 mAh g −1 even after 40 cycles, indicating good electrochemical performance. These good electrochemical performances could be attributed to the short Li-ion and electron pathways , and enough elastic buffer space to accommodate large volume variation of the special yolk–shell hierarchical structure.