Electrophoretic Deposition (EPD): An Alternative To Obtain Better Polymer Aluminium Electrolytic Capacitors

The presence of liquid electrolytes in supercapacitors ensures an adequate ion mobility and, at the same time, good contact is achieved between porous electrodes and the electrolyte which is translated in good capacitive properties. However, liquid electrolytes limit the energy density due to their stability potential window and they can undergo undesired reactions causing either degradation or gas evolution that can lead to the disruption of the capacitor1. As a solution to overcome these issues, the liquid electrolyte can be substituted by a solid material. Conductive polymers (CPs) represent good candidates as replacements for the liquid counterparts as these can be deposited onto electrodes, present good conductive properties and can withstand higher temperatures. Among these, poly(3,4-ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS) attracted most of the attention in the field for its outstanding properties2. Besides, adding different dopants allows to finetune PEDOT:PSS properties before and after the layer has been deposited3. When PEDOT:PSS is applied prepolymerized in the form of an aqueous ink onto a porous electrode to form an intimate contact, an in situ polymerization step is prevented resulting in a faster and greener production of devices. However, it has been observed that the impregnation of such electrodes is not optimal as a consequence of the increased viscosity of PEDOT:PSS water dispersions4. With the goal of obtaining optimally coated porous electrodes, an electrophoretic deposition5,6 (EPD) is proposed as a viable technique to improve the penetration of the dispersion into a porous metallic electrode, typically aluminium. Due to the charged nature of PEDOT:PSS colloids in water, thanks to the application of a bias between the porous electrode and a counter electrode, PEDOT:PSS is forced to diffuse towards the surface of the active electrode. In the present work, Aluminium/Al2O3/PEDOT:PSS systems are produced and later on analyzed via electrochemical and surface analysis techniques. The electrochemical techniques will provide information about the capacitance and the electrochemical series resistance of the stack and the surface analysis techniques will provide information about the contact between the two electrodes. The analysis of both combined will give rise to the optimal set of parameters to achieve adequate films thanks to EDP.