Facile solvothermal synthesis and superior lithium storage capability of Co3O4 nanoflowers with multi-scale dimensions

In this study, Co3O4 nanoflowers (Co3O4-NFs) have been successfully synthesized by a facile ammoniaassisted solvothermal process and subsequent heat treatment. By suitably increasing ammonia solution added during solvothermal synthesis, flower-like Co3O4 structures were tailored from nanoflowers to microflowers (Co3O4-MFs). Materials characterization indicated that Co3O4-NFs with a specific surface area as high as 103.9 m(2) g(-1) were composed of multi-scale dimensions, including nanoparticles (0D) of about 10 nm in size, nanosheets (2D) of about 10 nm in thickness and nanoflowers (3D) of 290 +/- 25 nm in diameter. The unique structural characteristics were beneficial for fast lithium ion diffusion and efficient electron transport. In addition, the mesoporous structure (22.6 nm) and the large pore volume (0.587 cm(3) g(-1)) of Co3O4-NFs were favorable for effectively alleviating volume expansion problems of high-capacity anode materials during charge-discharge cycles. When Co3O4-NFs were investigated as anode materials for lithium ion batteries, superior lithium storage capability, excellent cycling stability and C-rate performance were achieved, in comparison with Co3O4-MFs and commercial Co3O4 micro-/ nanoparticles (Co3O4-NPs). Specifically, when tested at a current density of 500 mA g(-1) for 100 cycles, the reversible specific capacity of 1323 mA h g(-1) was achieved for Co3O4-NFs, much higher than Co3O4-MFs (1281 mA h g(-1)) and Co3O4-NPs (107 mA h g(-1)). When current densities of C-rate tests were increased to 1000, 2000 and 3000 mA g(-1), Co3O4-NFs could still deliver average specific capacities of around 1081, 925.9 and 570.8 mA h g(-1), respectively. Owing to the intriguing merits from the unique characteristics, Co3O4-NFs with a nanoflower structure could achieve remarkable lithium storage capability, demonstrating great potential in next-generation lithium ion batteries.