Resistance distribution in electrochemical capacitors with a bipolar structure

The distribution of internal resistance in a 5-cell electrochemical capacitor comprising an electrode material with 80 wt.% RuO2·xH2O and 20 wt.% activated carbon and an electrolyte of 38 wt.% H2SO4 acid solution was analyzed. It was found that over 94% of the internal resistance in the capacitor was contributed to various contacts with the current collector of the conducting plastic sheet. Careful analysis of three different contact sources including the current collector to the end metal plate, the current collector to the neighboring current collector, and the current collector to the electrode, it was found that the resistance was dominated by the contact resistance between the current collector and the electrode. A composite current collector, made with conducting plastic sheet coated with metal films on both surfaces, was proposed for reducing all kinds of contact resistances. Using the composite current collector, the internal resistance can be reduced to about only 26% of that using conventional conducting plastic sheet.