Construction and electrical properties of 700 V aluminium polymer electrolytic capacitors

A process for the construction of a high voltage aluminium polymer electrolytic capacitor with operation voltages of up to 700 V is presented in this paper. Thin 150 μm, high purity aluminium films are anodized at a constant voltage with various anodization steps in a dilute boric acid solution to voltages between 1000 V and 1500 V. Single capacitor stacks were built, using the anodized aluminium, commercial cathode foils, paper separator and a PEDOT:PSS electrolyte. The resulting capacitors were electrically characterized by their capacitance, equivalent series resistance, breakdown voltage, and leakage current. Capacitance measurements showed that the thickness of the oxide film grew linearly with the forming voltage. The breakdown voltage exhibits a saturation behaviour with rising forming voltages, meaning that thicker oxide grown at voltages higher than 1000 V does not lead to proportional higher breakdown voltages. Oxide investigations showed that many defects are present at the surface at the highest forming voltages. Cross sections showed that the oxide underneath these defects have many voids that presumably lead to an earlier breakdown. Nonetheless, at a forming voltage of 1500 V, the breakdown voltage of the capacitor cells is at an average of 789 V with some samples going up to 800 V, which is more than three times the rated voltage of state-of-the-art devices.