The effect of salt concentration in electrolytes on the maximum energy storage for double layer capacitors

Double layer capacitors made with activated carbon electrodes and filled with nonaqueous electrolytes at different salt concentrations have been studied. It was found that the performance of the capacitor is strongly dependent on the salt concentration in the electrolyte. For electrolytes with high salt concentrations, the maximum energy stored in the capacitor is limited by the capacitance of the electrode material. For electrolytes with low salt concentrations, the maximum operating voltage as well as the maximum energy decreases with decreasing salt concentration. It has been demonstrated from ac impedance measurements that the decay of the maximum energy is due to the depletion of free ions in the electrolyte. The maximum energy storage in double layer capacitors with electrolytes at different salt concentrations was measured and was found to agree with the theory developed previously. From the study of de charge and discharge cycles at different constant current rates, it was found that the power performance of the capacitor is also strongly dependent on the salt concentration in the electrolyte.