Effect of Impregnation of PEDOT:PSS in Etched Aluminium Electrodes on the Performance of Solid State Electrolytic Capacitors

Electrolytic capacitors store larger amounts of energy thanks to their thin dielectric layers and enlarged surface area. However, the benefits of using a liquid electrolyte are at the expense of the possibility of leakage, evaporation, or rupture of the device over time. As a solution, solid electrolytes, such as conductive polymers, substitute the liquid ones decreasing the internal resistance and enlarging the lifetime of these devices. PEDOT:PSS is a widely used conductive polymer in the formation of solid electrolytic capacitors. However, using the enlarged surface of the porous electrodes efficiently requires industrial processes, the efficacy of which has not been explored. In this work, porous aluminium electrodes with dielectric layers of different thicknesses were coated with PEDOT:PSS at different levels of doping in order to study the efficiency of the production of solid electrolytic capacitors in industry. The combination of odd random phase electrochemical impedance spectroscopy (ORP-EIS) with surface characterization techniques (SEM-EDX, GDOES) formed a methodology that allowed the study of both the electrical properties and the level of impregnation for these model systems. All samples consisting of a porous aluminium electrode with an amount of PEDOT:PSS deposited on top resulted in an inefficient degree of penetration between the two electrodes. However, the electrochemical analysis proved that the use of dopants produces systems with the highest capacitive properties. Consequently, the evolution towards better solid electrolytic capacitors does not rely solely on the proper coverage of the porous electrodes, but on the proper electrical properties of the PEDOT:PSS within the pores.