High-performance MnO₂-deposited graphene/activated carbon film electrodes for flexible solid-state supercapacitor

High theoretical capacitance of MnO₂ nanoparticles were successfully electrodeposited on the conductive graphene/activated carbon (GN/AC) composite film, and the urchin type MnO₂ microspheres were controlled by adjusting the electro-deposition reaction times. The GN/AC/MnO₂-1200s composite electrodes exhibited a maximum specific capacitance of 1231 mF/cm² (MnO₂ loading mass of 7.65 mg/cm² and the mass specific capacitance of 123 F/g) at a current density of 0.5 mA/cm². The assembled flexible solid-state symmetric supercapacitor had a good mechanical flexibility (about 88.6% of its original capacitance after 500 bending times) and prominent cycling stability (about 82.8% retention in capacitance over 10000 cycles). More importantly, the device could possess a maximum energy density of 0.27 mW h/cm³ and a maximum power density of 0.02 W/cm³. These results well demonstrate a great potential for applications of GN/AC/MnO₂ composite electrodes in flexible energy storage devices.