Hierarchical porous arrays of mesoporous Co3O4 nanosheets grown on graphene skin for high-rate and high-capacity energy storage

The rate capability of an anode material is limited by slow Li-ion diffusion dynamics within the bulk, which leads to slow charging rates and low power densities in Li-ion batteries. To address this issue, we fabricated novel 3D hierarchical porous oxide arrays composed of mesoporous Co 3 O 4 nanosheets grown on a thin layer of reduced graphene oxide “skin” as a stable buffering and conducting layer. The porous oxide-graphene hybrid anode shows the outstanding rate capability (∼1400 mAh g −1 at 2.0 A g −1 ) among all oxide anode materials, high cycling stability and high retention of 84.5% over 200 cycles. Besides, the anode material in sodium-ion batteries also delivers a high capacity of 757 mAh g −1 and a high retention of 89.7% over 400 cycles. The high electrochemical performances are mainly due to mesoporous Co 3 O 4 nanosheets provide abundant accessible sites for electrolyte diffusion and intercalation of Li + /Na + ions into the active phases while the graphene coating dramatically boosts the overall Li/Na storage performances of the Co 3 O 4 nanosheets by enhancing the binding to and electrical contact with the current collector. Kinetic analysis reveals that the rational integration of battery-type and capacitor-type electrochemical energy storage in the same anode material (the distinct 3D hierarchical porous structure) enables to offer excellent rate capability. This novel graphene-metal oxide nanopore array could be applied in high-performance Li-ion and Na-ion batteries.