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 185 mAh g(-1) in specific discharge capacity under 10A g(-1) in current density. Assuming that an operating voltage of 2.5 V, this capacity corresponded 20 kW kg(-1) in power density and 90 Wh kg(-1) in energy density. (C) 2003 Elsevier B.V. All rights reserved.