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

Abstract

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.