Self-assembled microspheres composed of porous ZnO/CoO nanosheets for aqueous hybrid supercapacitors

Hybrid supercapacitors (HSCs) are attractive in the field of energy storage systems, which can offer higher energy density than capacitors and higher power density than batteries. However, the battery-type electrodes in HSCs often suffer from low rate capability and cycling performance due to their poor electrical conductivity. Here, we demonstrated a positive battery-type electrode by using self-assembled flower-like microspheres (MSs). The MSs were composed of porous ZnO/CoO nanosheets. Compared with pristine CoO and ZnO electrodes, the ZnO/CoO composite electrode shows enhanced electrochemical performance with high specific capacity as well as high rate capability. A high capacity of 85 mAh g(-1) (similar to 681 F g(-1)) is achieved at a high current density of 20 A g(-1). Such a favorable performance can be attributed to the ZnO introduction, which improves the electrical conductivity of the electrode, and the porous structure with interconnected pores, which provides fast ion/electron transport. When assembled with activated carbon, the HSCs can deliver high energy density (23.8 Wh kg(-1)) and power density (1.3 kW kg(-1)).