MnO2 nanospheres electrode composed of low crystalline ultra-thin nanosheets for high performance and high rate supercapacitors

In this work, we report an alternative approach to self-assemble low crystalline ultra-thin MnO2 nano-sheets into MnO2 nano-spheres by a cost-effective, one-pot and instant ultrasonic synthesis without the assistance of acid or template within an hour for high performance and high rate supercapacitors. The MnO2 nano-spheres are demonstrated to be excellent working electrodes in a three-electrode cell revealing remarkable specific capacitance of 309 F g(-1) at the current density of 1.0 A g(-1) and good cyclic stability with capacitance retention of 90% after 5000 cycles in 1 M Na2SO4 electrolyte aqueous solution. Further, an aqueous asymmetrical supercapacitor (MnO2//AC) device was constructed whose maximum workable potential window for the MnO2//AC device reached 0-2.0 V. MnO2//AC illustrated an energy density of 40 Wh kg(-1) with a maximum power density of 19000 W kg(-1). Besides, this device sustained a long cycle life with 85% capacitance retention after 5000 cycles.