Current collectors for low resistance aqueous flexible printed supercapacitors

In this paper we propose various current collector alternatives to be used in flexible supercapacitors with aqueous electrolyte when low equivalent series resistance (ESR) is required. The current collector material should be corrosion resistant when in contact with the saline electrolyte. Simultaneously it should have high electrical conductivity. In addition, environmental and cost aspects must be taken into account. We report supercapacitors with current collectors made of two different thicknesses of graphite foil (25 mu m and 150 mu m) and aluminium coated with graphite inks. These disposable and non-toxic supercapacitors show remarkable improvements in ESR compared with values obtained for similar components with current collectors made of graphite ink. When graphite foil or aluminium is used as current collector, the ESR can be decreased by more than 80 % compared to using graphite ink alone. Supercapacitors using a dense graphite protective layer on top of aluminium showed no sign of corrosion and their performance was not significantly reduced after ageing for 950 days. With graphite foils, comparable ESR values can be obtained as with aluminium. The graphite foil is an interesting alternative if metal materials should be avoided, e.g. to facilitate incineration of the supercapacitors together with regular household waste. Especially with non-porous graphite foil, we obtained properties suitable for practical applications.