Surface-reconstructed formation of hierarchical TiO2 mesoporous nanosheets with fast lithium-storage capability

Two-dimensional (2D) materials with a surface hierarchy and heterostructure offer infusive opportunities as high-rate electrodes in energy-storage/-conversion technologies due to their largely exposed active sites and shortened diffusion distance that are beneficial for mass/ion transfer. However, these 2D materials are still difficult to be synthesized due to the lack of a rational approach to design a surficial hierarchical heterostructure on 2D nanostructures. Herein, we explore a top-down strategy for the simple synthesis of surface-engineered TiO2 nanosheets with a large surface area, abundant open pores and TiO2-B/anatase heterointerfaces under mild conditions. Benefiting from the structural features of high electrode/electrolyte contact areas and short Li+/electron transport pathways, the surface-engineered TiO2 nanosheet material, tested as the lithium-storage electrode, show fast lithium uptake/release properties. A specific capacity of 149 mA h g(-1) is observed at a high rate of 10 A g(-1), and long-term operating stability is shown by delivering 110 mA h g(-1) at 6 A g(-1) upon 1000 cycles. Furthermore, the as-assembled lithium-ion capacitor using surface-engineered TiO2 nanosheets exhibits high energy density at high rates and possesses very stable cycling performance (similar to 80% capacity retention at 4 A g(-1) after 10 000 cycles). This study may pave a new way for designing novel 2D nanoarchitectures with a surface hierarchical structure for high-power energy-storage applications.