Hydrothermal-template synthesis and electrochemical properties of CoO/nitrogen-doped hemisphere-porous graphene composites with 3D heterogeneous structure.

Despite the high capacity of CoO employed in lithium-ion battery anodes, the reduced conductivity and grievous volume change of CoO during long cycling of insertion/extraction of lithium-ions remain a challenge. Herein, an optimized nanocomposite, CoO/nitrogen-doped hemisphere-porous graphene composite (CoO/N-HPGC), is synthesized by a facile hydrothermal-template approach with polystyrene (PS) microspheres as a template. The characterization results demonstrate that CoO nanoparticles are densely anchored onto graphene layers, nitrogen elements are successfully introduced by carbamide and the nanocomposites maintain the hemispherical porous structure. As an anode material for lithium-ion batteries, the composite material not only maintains a relatively high lithium storage capacity (the first discharge specific capacity can reach 2696 mA h g), but also shows significantly improved rate performance (1188 mA h g at 0.1 A g, 344 mA h g at 5 A g) and enhanced cycling stability (683 mA h g after 500 cycles at 1 A g). The enhanced electrochemical properties of CoO/N-HPGC nanocomposites can be ascribed to the synergistic effects of CoO nanoparticles, novel hierarchical structure with hemisphere-pores and nitrogen-containing functional groups of the nanomaterials. Therefore, the developed strategy can be extended as a universal and scalable approach for integrating various metal oxides into graphene-based materials for energy storage and conversion applications.