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 ammonia-assisted 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 m2 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 cm3 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.