Room-temperature synthesis of Co(OH)2 hexagonal sheets and their topotactic transformation into Co3O4 (1 1 1) porous structure with enhanced lithium-storage properties

The β-Co(OH)2 sheets with uniform hexagonal shape were prepared using NaBH4 as the structure directing agent at room temperature. After thermal annealing in air at 450 °C for 2 h, the as-prepared β-Co(OH)2 sheets were converted into porous Co3O4 with the hexagonal sheet-like morphology (H-Co3O4). The textural properties of the as-prepared samples were characterized by field-emission scanning electron microscopy, transmission electron microscopy and powder X-ray diffraction. The results of lithium storage capability indicate that the H-Co3O4 electrode exhibits excellent cycleability and rate capacity. At a charge/discharge current density of 50 mA g−1, a reversible capacity of 914 mAh g−1 can be maintained after 40 cycles. When the current density is increased to 1600 mAh g−1, a reversible capacity of 800 mAh g−1 can be still obtained. The superior electrochemical performance is attributed to the porous 2D structures with a finite lateral size and enhanced open-edges, which facilitate Li-ion and electron diffusion through active materials.

► The β-Co(OH)2 hexagonal sheets have been successfully synthesized at room temperature.
► The Co(OH)2 can be easily transformed into porous Co3O4 hexagonal sheets through annealing.
► These porous Co3O4 sheets exhibit excellent cyclic performance and high rate capacity.