High Performance Aluminum Solid Electrolytic Capacitors Using Self-Doped Poly(3,4-ethylenedioxythiophene)

Highly conductive fully water-soluble self-doped poly(3,4-ethylenedioxythiophene) (S-PEDOT) was first synthesized by electrochemical polymerization at different current densities between 0.5 and 5 mA cm–2. The electrical conductivity of S-PEDOT increased in proportion to the current density and reached 427 S cm–1 at 5 mA cm–2, which was an order of magnitude greater than previously reported for electrochemically polymerized self-doped PEDOT. The improvement in electrical conductivity was due to increased carrier mobility resulting from improved crystallinity, while the carrier density remained constant regardless of the current density. Furthermore, the S-PEDOT was applied to the cathode material of Al solid electrolytic capacitors. The highly conductive and fully dissolved S-PEDOT was found to efficiently penetrate into the fine etching pits in the etched anodized Al foil and achieved a low equivalent series resistance and a high capacitance utilization rate of 92%, which was superior to capacitors using commercial PEDOT doped with poly(4-styrenesulfonate) (PEDOT:PSS) colloids.