Graphene-wrapped MnO2 achieved by ultrasonic-assisted synthesis applicable for hybrid high-energy supercapacitors

Graphene-wrapped MnO2 was prepared via a solution-based ultrasonic-assisted method. The porous MnO2 microspheres wrapped with graphene nanosheets exhibit high specific surface area, facilitating fast ion diffusion/transport. The graphene-wrapped MnO2 demonstrates superior electrochemical performance (1227 F g−1 at 0.5 A g−1 and retaining nearly 90% of the initial capacity after 5000 cycles at 2 A g−1) to the MnO2 microsphere (728 F g−1 at 0.5 A g−1 and capacity retention of 83.7% after 5000 cycles at 2 A g−1). Moreover, the asymmetric supercapacitor based on the graphene-wrapped MnO2 reveals a high energy density of 19.6 Wh kg−1 at a power density of 351 W kg−1, demonstrating a great potential as the electrode material for energy storage devices.