Heterojunction TiO2@TiOF2 nanosheets as superior anode materials for sodium-ion batteries

Anatase TiO2 is considered as a promising anode material for sodium-ion batteries, but the inherent semiconductor properties and the sluggish Na+ diffusion kinetics limit its further development. To overcome these inherent drawbacks, heterojunction TiO2@TiOF2 constructed with two-dimensional nanosheets is prepared by the hydrothermal method. When heterojunction TiO2@TiOF2 is used as a sodium ion battery material, a stable cycling performance of up to 10 000 cycles can be achieved at a high current density of 5000 mA g−1, probably due to the heterojunction structure, the exposed (0 0 1) facet of TiO2 and the in situ formed NaF protective layer. Density functional theory (DFT) calculations further reveal that the heterostructure TiO2@TiOF2 nanosheets possess better electrical conductivity and lower formation energies of Na+ ions than those of the separated TiO2 and TiOF2. This work offers a new strategy to design novel heterojunction structures for the electrochemical sodium storage.