These two layers of charge, which are called an electrical double layer, constitute a capacitor. Because the separation of the layers is atomically small, the capacitance of an electrical double layer is huge. Electrical double-layer capacitors (EDLCs) are energy storage devices which utilize the electric charge of the electrical double layer.
Because the separation of the layers is atomically small, the capacitance of an electrical double layer is huge. Electrical double-layer capacitors (EDLCs) are energy storage devices which utilize the electric charge of the electrical double layer. EDLC consists of a pair of electrodes which are called the positive and negative electrodes.
In supercapacitors, the electrical double layer formed next to a large-area electrode and an electrolyte is effectively used, and hence these devices are technically called electric double-layer capacitors (EDLCs). At this stage, it is worth summarizing the difference between electrochemical (EC) cells and electrochemical capacitors.
Because an electrochemical capacitor is composed out of two electrodes, electric charge in the Helmholtz layer at one electrode is mirrored (with opposite polarity) in the second Helmholtz layer at the second electrode. Therefore, the total capacitance value of a double-layer capacitor is the result of two capacitors connected in series.
The double-layer capacitance is the physical principle behind the electrostatic double-layer type of supercapacitors. Simplified view of a double-layer of negative ions in the electrode and solvated positive ions in the liquid electrolyte, separated by a layer of polarized solvent molecules.
For large current discharge applications, internal resistance should therefore be kept as low as possible. When an electric double layer capacitor is charged for an extended period of time, the charge current decreases but it does not become zero. Rather it settles at a certain constant value, which is called the leakage current.