Electrical double-layer capacitors (EDLC) are, together with pseudocapacitors, part of a new type of electrochemical capacitors called supercapacitors, also known as ultracapacitors. Supercapacitors do not have a conventional solid dielectric.
Two storage principles determine the capacitance value of an electrochemical capacitor: Double-layer capacitance – electrostatic storage of the electrical energy achieved by separation of charge in a Helmholtz double layer at the interface between the surface of a conductor electrode and an electrolytic solution electrolyte. The separation of charge distance in a double-layer is on a few Ångströms (0.3–0.8 nm) and is static in origin. Pseudocapacitance – Electrochemical storage of the electrical energy, achieved by redox reactions electrosorption or intercalation on the electrode surface by specifically adsorbed ions that results in a reversible faradaic charge transfer on the electrode. Double-layer capacitance and pseudocapacitance contribute to a supercapacitor’s total capacitance value. However, the ratio of the two can vary greatly, depending on the electrodes’ design and the electrolyte’s composition.
Pseudocapacitance can increase the capacitance value by order of magnitude over the double layer. Supercapacitors are divided into three families based on the design of the electrodes: Double-layer capacitors – with carbon electrodes or derivatives with much higher static double-layer capacitance than the faradaic pseudocapacitance Pseudocapacitors – with electrodes made of metal oxides or conducting polymers with much higher faradaic pseudocapacitance than the static double-layer capacitance Hybrid capacitors – capacitors with special electrodes that exhibit both significant double-layer capacitance and pseudocapacitance, such as lithium-ion capacitors Supercapacitors have the highest available capacitance values per unit volume and the most considerable energy density of all capacitors.
They can have capacitance values of times that of electrolytic capacitors, up to F at working voltages of V. Supercapacitors bridge the gap between capacitors and rechargeable batteries. In terms of specific energy, as well as in terms of special power, this gap covers several orders of magnitude. However, batteries still have about ten times the capacity of supercapacitors. While existing supercapacitors have energy densities of approximately 10% of a conventional battery, their power density is generally 10 to 100 times as great. This makes the charge and discharge cycles of supercapacitors much faster than batteries.Additionally, they will tolerate many more charge and discharge cycles than batteries. ITheelectrolyte is the conductive connection between the two active electrodes in these electrochemical capacitors. This distinguishes them from electrolytic capacitors, where
Supercapacitors are polarized and must operate with the correct polarity. Polarity is controlled by design with asymmetric electrodes or, for symmetric electrodes, by a potential applied during manufacture. Supercapacitors support a broad spectrum of power and energy requirements applications, including Long duration low current for memory back up in (SRAMs) Power electronics that require very short, high wind, as in the KERS system in Formula 1 cars Recovery of braking energy in vehicles.