High-rate and high conductivity mesoporous TiO2 nano hollow spheres: Synergetic effect of structure and oxygen vacancies

TiO2 is exceptionally useful anode material for Li-ion batteries, and the ability to modify TiO2 makes it a very attractive and challenging research object for use in different functional materials. In this paper, mesoporous TiO2 nano hollow spheres (dubbed TiO2-1 andTiO2-2) with moderate oxygen vacancies were successfully prepared. Structure and composition characterizations revealed that the spheres had a hollow structure, surface oxygen vacancies and an excellent Ti3+/Ti4+ molar ratio of 0.181. In addition, TiO2-2 demonstrated synergistic effects in terms of electron and lithium ion transportation, with impedances as low as 3.05 Ω, and its Li-ion diffusion coefficient (7.8 × 10−12 cm2 s−1) was at least a factor of 10 larger than that of TiO2-1(6.2 × 10−13 cm2 s−1). More importantly, experiments demonstrated that the well-balanced Li+/e− transportation arising from the synergetic effect between structure and Ti3+/oxygen vacancy in the optimal TiO2-2 sample had a high specific capacity of 233 mAh·g−1 at 0.1C, and 79.8% capacity retention after 100 cycles, as well as greatly enhanced rate performance and electrochemical reactivity and stability in comparison with the other TiO2. Our method for creating oxygen vacancies in TiO2 nano hollow spheres can be generalized to other electrochemical energy storage materials.