Hierarchical TiO2 Hollow Nanospheres: Ultra Stable Anode for Na-Ion Batteries

Amorphous TiO₂@C nanospheres were synthesized via a template approach. After being sintered at different condition, two polyphase TiO₂ hollow nanospheres were obtained. The electrochemical properties of amorphous TiO₂ nanospheres, and different phase TiO₂ hollow nanospheres as anodes for the Na-ion batteries were characterized. It was found that all of them demonstrated the excellent cyclability, which can sustainable for thousands of cycles with tiny capacity fading. By comparison, the anatase TiO₂ presented higher capability than that of rutile TiO₂ and amorphous TiO₂. Through the crystallography analysis, it was revealed that anatase TiO₂ crystal structure supplies 2-dimension diffusion path for the Na ions intercalation and more accommodation sites. Density functional theory (DFT) calculation indicates lower energy barriers for Na⁺ inserting into anatase TiO₂. Therefore, anatase TiO₂ hollow nanospheres show the well-defined high rates performance. Via the ex-situ FESEM analysis, it was revealed that the TiO₂ hollow nanospheres architecture can be maintained for thousands cycles, which is the main reason for its superior cyclablity.