Micro-/nano-structured hybrid of exfoliated graphite and Co₃O₄ nanoparticles as high-performance anode material for Li-ion batteries

A novel Co₃O₄ nanoparticles (NPs)/exfoliated graphite (EG) composite has been prepared through a stirring-assistant hydrothermal route and a subsequent post-anneal treatment. Results of microstructure characterizations of XRD, FE-SEM and HR-TEM analyses indicate that high-crystallized Co₃O₄-NPs with a dimension of ∼5 nm are homogenously anchored on the nanosheets of EG in the form of tiny agglomerates of ∼20 nm. Restack and shrinkage of the edge regions of EG are distinctly observed after suffering from the hydrothermal process, which exerts a positive influence over the decay-free cycling ability of the Co₃O₄-NPs/EG electrode. The reversible capacity increases with cycling, and reaches 1183 mAhg⁻¹ (94th cycle) at 100 mAg⁻¹ and 739 mAhg⁻¹ (100th cycle) at 1000 mAg⁻¹. After suffering from 800 cycles at 2000 mAg⁻¹ and resetting to 100 mAg⁻¹, the charge capacity recovers to as high as 1225 mAhg⁻¹ immediately, and stabilizes in the following cycles. The decay-free cycling performances and good rate capability are ascribed to the favorable synergistic effect between Co₃O₄-NPs and the robust/conductive skeleton of EG. In addition, an exceeded capacity which much surpasses the calculated theoretical value is achieved, further proving the good synergistic enhancement due to the high-effective integration between Co₃O₄-NPs and EG.