Supercapacitors

Supercapacitors, also known as electrochemical capacitors, are energy storage devices that bridge the gap between traditional capacitors and batteries. They store energy mainly by electrostatic charge separation at electrode-electrolyte interfaces or, in some devices, by fast surface redox reactions. This configuration yields very high power density and long cycle life.

Most commercial supercapacitors are electric double-layer capacitors (EDLCs). They use high-surface-area carbon electrodes in an electrolyte to form an electric double layer at the interface. Energy storage is primarily physical, with minimal chemical change in the electrode material, enabling rapid charge and discharge.

Pseudocapacitors store energy through fast, reversible redox reactions on or near the electrode surface. Materials such as transition metal oxides, conductive polymers, or metal sulfides contribute additional capacitance, yielding higher energy density than EDLCs but often at the expense of cycle stability and cost.

In performance terms, supercapacitors offer very high power density and long cycle life, often exceeding 100,000 cycles. Compared with batteries, they have lower energy density, meaning shorter run times between charges. Typical operating voltages per cell depend on the electrolyte, with organic electrolytes supporting roughly 2.5–2.7 V per cell.

They are used for rapid power delivery and short-duration energy buffering in transportation (for example, regenerative braking and start-stop systems), telecommunications, uninterruptible power supplies, and electronics requiring fast bursts of energy or extended cycle life.

Limitations include relatively low energy density, cost and material availability for certain chemistries, temperature sensitivity, self-discharge, and aging effects with some pseudocapacitive materials. Hybrid devices combine features of batteries and supercapacitors to balance energy and power needs.