Nanostructure and high-rate discharge-charge property of manganese oxide/acetylene black nanocomposite synthesized by sonochemical method

Nanostructure and high-rate discharge-charge capacities were investigated for the manganese oxide/acetylene black (AB) nanocomposites fabricated by sonication from aqueous solutions containing permanganate ion. Coating structure in which the acetylene black particles were uniformly coated with manganese oxide was successfully prepared from a pH=10 solution. On the other hand, acicular and tabular birnessite crystals were observed in samples obtained from pH<1 solutions, although the formation rate of manganese oxide in the pH<1 solution was much faster than that in the pH=10 solution. The sample from the pH=10 solution could be discharged and charged under high current density, such as 10 A g−1, because of the unique nanostructure. In contrast, a large decrease in the specific capacity was observed for the sample synthesized from the pH<1 solution under 10 A g−1 due to the excessive formation of manganese oxide and the disadvantage in the electronic conduction and lithium diffusion of the birnessite.