The present invention is directed to a conductive polyethylenedioxythiophene (PEDOT)
polymer coated
electrode adapted for use as a
cathode electrode of an
electrolytic capacitor and a method of manufacturing the same. According to the present invention, a
metal foil substrate is placed in an
aqueous solution of a doped 3,4-ethylenedioxythiophene (EDOT)
monomer and a co-
solvent, to dissolve the EDOT
monomer, and a current is applied until the desired thickness of the
polymer coating is electrochemically deposited. Additionally, an
organic acid is added to the
aqueous solution to act as an oxidizer. In order to improve the uniformity and adherence of the
coating a surfactant may also be added. In a preferred embodiment, the EDOT
monomer and cosolvent are first mixed, and then added to a water solution of oxidizer and
dopant. The
polymer film is deposited electrochemically onto the substrate by applying a
DC current between 0.05 mA / cm2 and 5.0 mA / cm2 for 1 to 60 minutes, more preferably between about 0.13 mA / cm2 to about 0.26 mA / cm2 for between 9 and 18 minutes, such that a conductive polyethylenedioxythiophene (PEDOT)
coating is formed on the
electrode surface. According to the present invention, the increased surface area of the coated
cathode results in lower gas generation and, therefore, reduced
capacitor swelling, reduced
oxide buildup on the
cathode and prevention of
electrolysis. The present invention results in electrodes with a minimum
capacitance of 1 mF / cm2. The present invention also makes it possible to use thinner electrodes than conventional aluminum electrodes, thereby reducing the physical dimensions of the
capacitor.