Fabrication and characterization of the hierarchical AAO film and AAO-MnO2 composite as the anode foil of aluminum electrolytic capacitor

Abstract Anodic aluminum oxide (AAO) film of different regular hierarchical pore structures and AAO-MnO2 composite of many homogeneously distributed microvoids have been prepared and comparatively characterized, mostly as they were adopted as an anode foil of aluminum electrolytic capacitors. Results showed that the hierarchical pore structure of AAO film is composed of a supernatant layer of larger holes and a rock-bottom layer of smaller holes. The smaller holes' density increases with the reduction of the secondary anodization voltage in the two-step anodization process of the AAO film, which subsequently enlarges the specific capacitance to 7.88 μF/cm2 and may also increase the leakage current when the AAO film is adopted as the anode foil in an aluminum electrolytic capacitor. The obtained hierarchical AAO-MnO2 composite, with a multi-layered interweaved structure, has not only significantly brought up the specific capacitance from 7.88 μF/cm2 to 25.56 μF/cm2 but also may significantly reduce the leakage current and consequently improve the stability when being used as the anode foil. Compared with merely increasing the surface area of AAO film, the introduction of high dielectric constant compounds into the AAO film without changing the actual surface area can improve the aluminum electrolytic capacitor's capacitance performance more effectively.