Formation of Al2O3–Nb2O5 composite oxide films on low-voltage etched aluminum foil by complexation–precipitation and anodizing

Niobium pentaoxide (Nb2O5) thin films were deposited on etched aluminum foils by complexation–precipitation followed by heat treatment. Then the Al2O3–Nb2O5 (Al–Nb) composite oxide films were formed by anodizing to increase the capacitance of anodized aluminum foils which are used in aluminum electrolytic capacitors. The composition and structure of niobium deposition layer were characterized by X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD), and the microstructures and dielectric properties of anodic oxide films were investigated by scanning electron microscope (SEM) and electrochemical impedance spectroscopy (EIS) respectively. The results show that the niobium deposition layer after heat treatment existed in the form of crystalline Nb2O5. The aluminum foil with Nb2O5 coating can be anodized with higher efficiency and energy saving. Compared with that of normal anodized aluminum foils, the effective area of the anodized aluminum foils with Al–Nb composite oxide films had no apparent change. The specimens with Al–Nb composite oxide films anodized at 30 V exhibited about 20% higher specific capacitance than that of those with pure aluminum oxide films. It suggests that the method of complexation–precipitation is an effective way to increase the specific capacitance of anodized aluminum foils used in aluminum electrolytic capacitors.