Modeling and Sizing of Supercapacitors

Abstract

Abstract —Faced with numerous challenges raised by the requirements of the modern industries for higher power and higher energy, supercapacitors study started playing an important role in offering viable solutions for some of these requirements. This paper presents the surface redox reactions based modeling in order to study the origin of high capacity of EDLC (electrical double-layer capacitor) for better understanding the working principles of supercapacitors. Some application-dependent sizing methods are also presented since proper sizing can increase the efficiency and the life cycle of the supercapacitor based systems. Index Terms—electrochemical capacitor, modeling, sizing, pseudo-capacitance I. INTRODUCTION Electrochemical capacitors have achieved substantial acceptance in the electronics industry, replacing backup batteries in many CMOS memory applications. Many of the first commercially available el ectrochemical capacitors were directed toward such applications and, consequently, were of limited size and power performance. As will be shown in the next sections, these limitations are not inherent in the technology, so larger, higher-voltage capacitors with greatly enhanced power performance have been available for several years from some suppliers and currently are being developed by others [18]. Different names like “double layer capacitors”, “supercapacitors” , “ultracapacitors” , “power capacitors” , “gold capacitors”, “power cache” were used to indicate different types of capacitors displaying high values of capacity, but the first mention of a double-layer electrochemical capacitor realizati on is made just in 1957, in a patent application of General Electric (Becker). [ 4] In 1966, SOHIO (Standard Oil Company, Cleveland, Ohio) patented a similar device having porous carbon electrode but with a higher energy density than that of General Electric. Further patents described improved SOHIO developed solutions in the following years, but their licenses are transferred to NEC which produced for the first time commercial devices under the name “supercapacitor”. The first high power electrochemical capacitors were produced in the years 1980 by Pinnacle Research Institute (PRI) for military applications like laser weapon and guided missiles with ruthenium/tantalum oxide electrodes under the name “PRI ultracapacitor”. [4] Nowadays, electrical double-la yer capacitors (EDLC) are gaining more attention due to their practical potential in applications areas with increasing power demands. Due to reversible electrochemical energy storage these capacitors can be recharged very quickly with best long cycle life. Energy storage is by means of st atic charge rather than of an electro-chemical process (inherent to common battery). New applications are emerging in fields like automotive engineering