One-step synthesis of mesoporous MnO2/carbon sphere composites for asymmetric electrochemical capacitors

Whisker-like MnO2/carbon sphere (MnO2/C) composites with a mesoporous structure are synthesized through an easy one-step hydrothermal method using glucose as the carbon source without any catalyst or template. Highly porous interconnected MnO2 nanowhiskers are uniformly coated on the surface of the carbon spheres to construct a mesoporous architecture. A high-voltage asymmetric electrochemical capacitor (EC) is assembled with active carbon as the negative electrode and MnO2/C spheres as the positive electrode in a neutral aqueous 5 M LiNO3 solution as an electrolyte. This aqueous electrolyte-based asymmetric EC is reversibly cycled within a wide voltage region of 0-2.0 V. Moreover, a high specific capacitance of 307.6 F g(-1), a superior long-term cyclic stability and a nearly 96.6% capacitance retention after 1000 cycles are observed.