Symmetric Pulsed Anodizing of Aluminum Foil for Aluminum Electrolytic Capacitors

Alumina as dielectric material is commonly prepared via anodizing high purity etched foils in electrolyte, which vitally determines the performance of aluminum electrolytic capacitor. However, the traditional direct-current (DC) anodizing is limited due to a large amount of Joule heat production, a space charge layer, and unnecessary side reactions, which result in great energy consumption and a poor quality of oxide film. In this work, the symmetric pulsed-current (SPC) anodizing is introduced into the anodization of aluminum foil for electrolytic capacitor. SPC anodizing can contribute to the diffusion of heat during the non-anodization period because of its pulse mode, lowering the thermally induced dissolution of alumina reacted with water. In addition, SPC anodizing can suppress the formation of a space charge layer by alternating the electric field so as to extract impurities out of the oxide film and lower the energy consumption. Moreover, the SPC samples own the denser barrier-type alumina, which have better crystallinity resulting in higher permittivity. Voltage-current output and side reactions during the anodizing process have been analyzed, demonstrating the lower energy consumption and higher production efficiency of the SPC method. In comparison with the DC anodized samples, the specific capacitances of SPC samples are elevated by 10.84% and the energy consumption of the SPC method is decreased by 25.5% in total. Therefore, the SPC anodizing method has a good prospect for industrialization of aluminum electrolytic capacitor.