Supercapacitors | Supercapacitors: Performance, cost, and applications

Abstract

Electrochemical capacitors (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 and cycle life than batteries. In general, supercapacitors 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. This article discusses the performance and applications of advanced electrochemical capacitors. Large numbers of small and mid-size cells are presently being manufactured and sold for consumer and industrial electronics applications. The markets for the large devices (1000–5000F) in vehicle and grid applications are presently relatively small primarily due to their high price and relatively low energy density. The vehicle applications of most current interest are engine starting and in hybrid- electric drivelines of various type vehicles. Vehicle applications of supercapacitors to date have used large carbon/carbon double-layer devices. In the last few years, hybrid supercapacitors have been developed and have come commercially available. The hybrid supercapacitors have much higher energy density (60–90Wh/L) than the double-layer cells (6–8Wh/L) cells. Vehicle simulations of hybrid-electric vehicles of various types using the hybrid supercapacitor technology has shown that the supercapacitors are lighter and smaller than lithium batteries and that the fuel economy of all the vehicles is higher using the supercapacitors. This is true for engine-powered hybrids as well as hybrids using hydrogen fuel cells. Increasing the energy density of the supercapacitors reduces their cost per kWh to be competitive with that of lithium batteries in the same vehicle. New markets for large supercapacitors are developing in electric buses and metro-trains as their energy density has increased. For these applications, units storing about 50kWh have been assembled using Aowei-China supercapacitors. These vehicles have been operating several years in Europe and China. The energy to recharge the supercapacitors comes both from regenerative braking and power provided along the route of the vehicle. New applications of supercapacitors are also developing to support smart electric grids. These applications also benefit from the higher energy density of the hybrid supercapacitors.