Mn3O4/MnOOH nanocomposite has been synthesized simply.
Mn3O4 were oxidized to MnOOH partly during ultrasonic irradiation process.
Mn3O4/MnOOH nanocomposites could be quickly conditioned.
A specific capacitance of 307.8 F g−1 was obtained for Mn3O4/MnOOH nanocomposite.