Engineering electroactive materials onto 3D conductive scaffolds holds promise to the development of high-performance energy storage devices. In comparison with the existing scaffolds made of metals or carbon nanomaterials, we herein report a unique scaffold of 3D nanostructured polyaniline (PANi) network, where MnO2 nanoflakes of 10 nm in thickness grow vertically to create a hierarchically structured composite. Through two simple sequential processes, a binder-free electrode with a high areal density of 8.3 mg cm(-2) (7.3 for MnO2 and 1.0 for PANi) is readily fabricated by using a piece of carbon cloth as the current collector. Measured with three electrode configuration at 5 mV s(-1), the network delivers capacitance of 423.7 F g(-1), 3516.7 mF cm(-2) and 106.6 F cm(-3), with retention of 98.5% over 10,000 cycles. The high capacitance especially areal capacitance is attributed to the maximum utilization of high-specific area MnO2 nanoflakes through efficient electron and ion transfer which is enabled by two intimate interfaces respectively between MnO2 and PANi and between PANi and carbon cloth. The superior cycling performance is mainly enabled by the volume-change accommodation of the hierarchically porous network. This composite network would provide a new methodology to maximize the electrochemical performance of metal oxides.