MECHANISM 1 • EDLC

The electric double layer

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An electric double-layer capacitor stores energy electrostatically, by physically separating ions. When a voltage is applied, ions in the electrolyte move through the liquid and adhere to the surface of the electrodes, forming a thin, dense layer of stored charge.

No electrons cross the interface — the ions just line up at the surface.

MECHANISM 1 • EDLC

Porous carbon, huge surface

EDLC electrodes are typically highly porous activated carbon, chosen for its enormous surface area — more surface means more room for ions to line up. Ions accumulate at the microscopic boundary between the solid electrode and the liquid electrolyte, forming two thin dense regions of charge known as the Helmholtz double layer.

solid electrode | Helmholtz double layer | electrolyte

Capacitance here scales with how much surface the ions can reach.

MECHANISM 1 • EDLC

What EDLCs are good at

Charge / discharge Typically in seconds

Cycle life Millions of cycles with virtually no degradation

Power Massive bursts of current thanks to low internal resistance

When the ions release from the surface and disperse back into the electrolyte, the stored energy is delivered — and nothing has been used up.

UNIT 6 STUDY COMPLETE

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Ready for the Fab Challenge?

You've covered how ions pile up at an electrode surface to store charge electrostatically.