Double-layered capacitors are electrostatic capacitors. The charge deposition is done in these capacitors according to the principle of Double-layer.

·        All solid substances have negative charge on the surface layer when disposed into a liquid.

·        This is due to the high dielectric coefficient of liquid.

·        All the positive ions come near the surface of the solid material to make a skin.

·        The deposition of positive ions near the solid material get looser with the distance.

·        The charge created at this surface due to the deposition of anions and cations leads to some capacitance value.

This double-layer phenomenon is also termed as Helmholtz double layer. The figure below explains the procedure of double-layer phenomenon, when the capacitor is charged and when it is discharged.

These capacitors are simply called as Electric Double Layered Capacitors (EDLC). They use carbon electrodes to achieve separation of charge between the surface of conductive electrode and the electrolyte. The carbon acts as dielectric and the other two as anode and cathode. The separation of charge is much smaller than in a conventional capacitor.