Formation and Property of Al2O3-TiO2 Composite Anodic Oxide Film on DC-Etched Al Foil for Al Electrolytic Capacitors

This research article aims to improve the specific capacitance of DC-etched Al foil for Al electrolytic capacitors by forming an Al2O3-TiO2 composite anodic oxide film. DC-etched Al foils for aluminum electrolytic capacitors were immersed in a TiO2 precursor sol, followed by calcination and anodizing to manufacture a TiO2-Al2O3 composite anodic oxide film. TiO2 precursor sol–gel particles after calcination were analyzed by XRD. During anodization, the anode potential with time was measured by a digital meter. A scanning electron microscope, electrochemical impedance measurements, and a general digital LCR meter were adopted to explore the microstructure and property of the anodic oxide films. The specific capacitance for the TiO2-Al2O3 composite anodic oxide film and a pure Al anodic one is 3.013 μF/cm2 and 2.435 μF/cm2 at C60V, respectively. The thickness is 87.26 nm for the former and 177.65 nm for the latter. The results show that the TiO2-Al2O3 composite anodic oxide film is about 51% thinner than the single Al anodic film, accounting for a large improvement in specific capacitance. The formation efficiency of the pretreated sample is much higher than that of the blank sample, owing to the pre-deposited TiO2 layer and thermal Al oxide layer. However, the composite anodic oxide film’s specific resistance was reduced and its dielectric loss was also aggravated, resulting from the doping-introduced structural defects.