Electrochemical capacitors (ECCs; sometimes referred to as supercapacitors or ultracapacitors) are energy storage devices that have much higher capacitance and energy density than the traditional dielectric capacitors that are presently sold in various markets by the billions each year. Electrochemical capacitors have much lower energy density and much higher power capacity than batteries. | Application A Burke University of California-Davis Davis CA USA 2009 Elsevier . All rights reserved. Introduction Electrochemical capacitors ECCs sometimes referred to as supercapacitors or ultracapacitors are energy storage devices that have much higher capacitance and energy density than the traditional dielectric capacitors that are presently sold in various markets by the billions each year. Electrochemical capacitors have much lower energy density and much higher power capacity than batteries. Hence ECCs have characteristics between traditional capacitors and batteries and can compete with both depending on the application. In general ECCs can be a serious alternative to batteries when the amount of energy to be stored is relatively small for a battery and the peak power requirement of the system is large compared to the average power. The ECC can be a serious alternative to traditional capacitors when the energy storage requirement is large for a traditional capacitor and the high power pulse times are not too short milliseconds or longer . The initially developed ECC devices had relatively low power capability as they were intended for use as energy storage for memory backup. Since the late 1980s ECCs with high power capability have been under development. Steady progress has been made over the past 15 years in increasing the energy density and reducing the cost of the high-power ECCs. Since 2000 there has been the expectation that large markets for ECCs would begin to develop and that in a few years large volumes of the devices would be sold for a number of applications. The markets for small devices especially those with capacitance less 1 F have developed at an increasing pace but the markets for the larger devices especially those with a capacitance of 1000 F and greater that compete with batteries have developed much slower than anticipated primarily because of the high cost of the large ECC devices. In the meantime improvements in battery technology
