Formation of Al₂O₃-BaTiO₃ composite thin film to increase the specific capacitance of aluminum electrolytic capacitor

To increase the specific capacitance of aluminum anodic foil, barium titanate BaTiO₃ (BT) sol was dip-coated on the etched aluminum foils by a sol-gel process. After annealed at different temperatures, the foils were anodized in ammonium adipate solution. The phase transition of BT powder was investigated. The voltage-time variations during anodizing were monitored, and the electric properties such as specific capacitance, dissipation factor, withstanding voltage, and leakage current of these foils were also examined. It was found that BT started to crystallize at 550°C. The anodizing time of the foils covered with BT films decreased with annealing temperature. The specific capacitance and the product of specific capacitance and withstanding voltage of anodic foils with a BT coating increased with annealing temperature, and the largest increases were about 46% and 39% compared to that without a BT coating, respectively. The obtained anodic foils with the largest specific capacitance were assembled into aluminum electrolytic capacitors, and the load and shelf life tests were measured. There was no significant difference between Al/BT-600 and Al during the load and shelf life tests. The capacitor life time is larger than 2500h. From the results, BaTiO₃ is promising to be used as the partial dielectric of aluminum electrolytic capacitor to increase the specific capacitance.