The nanocomposite material of amorphous manganese oxide and acetylene black (HSMO/AB), was synthesized by sonochemical method. The acetylene black particles were homogeneously coated with amorphous manganese oxide. In order to demonstrate that these characteristic structures were suitable for rapid discharge–charge, the composite material was tested under large current density. The result exhibited 185mAhg−1 in specific discharge capacity under 10Ag−1 in current density. Assuming that an operating voltage of 2.5V, this capacity corresponded 20kWkg−1 in power density and 90Whkg−1 in energy density.