Types of electrochemical capacitors

EFFECT OF CARBONACEOUS MATERIALS ON PERFORMANCE OF CARBON-CARBON AND CARBON-Ni OXIDE TYPES OF ELECTROCHEMICAL CAPACITORS WITH ALKALINE ELECTROLYTE... 

Testing in the Carbon-Carbon type of Electrochemical Capacitors... 

Three types of electrochemical capacitors (I, II, and HI) are known with ECPs as active electrode materials. Type I corresponds to a capacitor based on a symmetrical configuration with identical active materials based on p-doped ECPs (e.g., based on PPy) on both electrodes. Eigure 28.5 shows charging-discharge chrono-voltammograms characterizing the behavior of ECSCs with two PPy-based electrodes (Volfkovich and Sedyuk, 2002). As we see, they have the shape of straight lines for conventional capacitors. 

Conway, B. E., and W. G. Pell. 2003. Double-layer and pseudocapacitance types of electrochemical capacitors and their applications to the development of hybrid devices. Journal of Solid State Electrochemistry 7 637-644. 

Figure 15.6 Schematic representation of the three types of electrochemical capacitor that can be assembled with p- and n-dopable conducting polymers. The cell voltage that could be expected from these capacitors is given on the left-hand side of each capacitor type...

It was seen above that different types of electrochemical supercapacitors exhibit specific capacities many orders of magnitude higher than the film and electrolytic capacitors known before. It must be added at once, however, that the behavior of supercapacitors differs appreciably from that of ideal film capacitors. In contrast to... 

As it logically follows from the considered mechanism and the existing experimental data, PANI-type conductive polymers can certainly be used to improve the characteristics of electrochemical capacitors. According to our estimations, a specific capacity of electrodes with conductive polymers could be increased by as much as to 3-5 times over that of the classical carbon electrodes. 

A Model to Characterize the Impedance of Electrochemical Capacitors arising from Reactions of the type Oad + n e-. dblharw.r Rad. (Erratum to document cited in CA117(2) 15999r)... 

In general, the properties of electrochemical capacitors are quite different from those of other types of capacitors. Like batteries, electrochemical capacitors are essentially low-voltage devices their breakdown occurs by electrolysis of the electrolyte. For aqueous electrolytes, the thermodynamic potential at which this occurs is about 1.2 volts. For organic solvent-based systems, it may be as high as 3 or 4 volts, whereas, for silver and copper solid electrolytes, it is less than 1 volt. This property severely limits the amount of stored energy (U) for a given capacitance because U = 1/2CV. ... 

For electrochemical capacitors of the system carbon-carbon, in spite of the fact that the electrode body consists of conductive activated carbon, it is always necessary to use highly conducive additives, preferably those selected from the group of carbon materials. Exact type of additives plays a secondary role for this type of an EC, as it operates in the so-called safe voltage interval (l,12-l,24v), where limited to no oxidation of carbon takes place in this range of voltage. 

In the second type of supercapacitor, sometimes termed pseudocapacitors, redox capacitors or electrochemical capacitors, the non-Faradaic doublelayer charging process is accompanied by charge transfer. This Faradaic process must be characterized by extremely fast kinetics in order to allow device operation with high current density discharge pulses. 

Fig. 9.30 Constant current (200 mA) discharge curves for the three types of polymer electrochemical capacitor...

Types of capacitors and mode of energy storage after Ref.206 Reprinted from B.E. Conway, Electrochemical supercapacitors. Scientific Fundamentals and Technological Applications, Kluwer Academic/Plenum Publishers, New York (1999). Copyright 1999 with permission from Kluwer Academic Pubhshers. 

Recent application of conducting polymers for electrochemical capacitors has been reviewed. The ionically conducting polymers have the potential to replace wet-type capacitors by dry-type ones. Especially important are the gel electrolyte systems whose ionic conductivity is high, and thus high capacitance can be obtained with them in EDLC. We believe that the combination of high surface area... 

---