Hierarchically porous CoO microsphere films with enhanced lithium/sodium storage properties

Nanostructured transition metal oxides are very attractive as electrode materials for electrochemical energy storage. Herein, urchin-like CoO microsphere films are prepared by a low-temperature hydrothermal synthesis. The urchin-like CoO microspheres are composed of numerous nanoparticles, with a large specific surface area of 103 m2 g−1. For lithium storage, the CoO microsphere film electrode delivers a high reversible capacity of 950 mAh g−1 after 120 cycles at a current density of 200 mA g−1. In particular, a reversible capacity of 499 mAh g−1 is achieved after 250 cycles at a current density of 100 mA g−1 for first ten cycles and a current density of 500 mA g−1 for the 11th to 250th cycles, demonstrating the good rate capability and superior cycling stability of the film electrode. For sodium storage, the CoO microsphere film electrode shows a capacity of 172 mAh g−1 after 100 cycles at a current density of 100 mA g−1. Further, a reversible capacity of 156 mAh g−1 is obtained at a relatively high rate of 800 mA g−1. The enhanced lithium/sodium storage properties of the hierarchically porous CoO microsphere film electrode may be ascribed to its high specific surface area and free-standing film structure.