Electrochemical capacitors performance

FIGURE 2.70 Cyclic voltammograms for [EMIMllBFJ at 5 mV s" . (Sillars, F. B. et al. 2012. Variation of electrochemical capacitor performance with room temperature ionic liquid electrolyte viscosity and ion size. Physical Chemistry Chemical Physics 14 6094-6100. Reproduced by permission of The Royal Society of Chemistry.)... 

Jang JH, Han S, Hyeon T, Oh SM (2003) Electrochemical capacitor performance of hydrous ruthenium oxide/mesoporous carbon composite electrodes. J Power Sources 123 79-85... 

Kim, N. D. et al. 2008. Electrochemical capacitor performance of N-doped mesoporous carbons prepared by ammoxidation. Journal of Power Sources, 180, 671-675. 

Electrochemical capacitors are power storage devices, whose performance is based on the charge accumulation from an electrolytic solution through electrostatic attraction by polarized electrodes. The capacitance of this system is directly proportional to the electrode surface, therefore carbons are very efficient for this application because of various possibilities of their modification and creation of a controlled pore size distribution [1-3]. The electrostatic attraction of ions takes place mainly in micropores, however, the presence of mesopores is necessary for efficient... 

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

Carbonaceous materials play a key role in achieving the necessary performance parameters of electrochemical capacitors (EC). In fact, various forms of carbon constitute more than 95% of electrode composition [1], Double layer capacity and energy storage capacity of the capacitor is directly proportional to the accessible electrode surface, which is defined as surface that is wetted with electrolyte and participating in the electrochemical process. 

Miller JR. The Evolution of Electrochemical Capacitor Technology Future Performance Projections. 2003 International Conference on Advanced Capacitors, Kyoto, Japan, May 29-31,2003. 

Yu G, Hu L, Vosgueritchian M, Wang H, XieX, McDonough JR, Cui X, Cui Y, Bao Z. Solution-processed graphene/Mn02 nanostructured textiles for high-performance electrochemical capacitors, NanoLett 2011,11, 2905-2911. 

Novel, inexpensive synthesis routes for producing materials with precisely controlled nanotexture must be developed to improve the performance of batteries and electrochemical capacitors, as well as to enable new electrochemical applications of carbons. Two alternatives, carbide-derived carbon (CDC) and templated carbon, have shown a promise to offer the requisite control necessary to push device performance to the next level and will be explored in this chapter. 

In fact, it has been shown that the capacitance values for the composites with PANI and PPy strongly depend on the cell construction [92], With chemically deposited ECP, extremely high values of specific capacitance can be found—from 250 to 1100F g 1—using a three-electrode cell, whereas smaller values of 190F g 1 for MWNT/PPy and 360F g 1 for MWNT/PANI have been measured in a two-electrode cell. It highlights the fact that only two-electrode cells allow the materials performance to be well estimated in electrochemical capacitors. 

An extensive study has been performed to demonstrate a general approach to assess electrochemical capacitor reliability as a function of operating conditions on commercial capacitor cells [75,76], For the temperature dependency an Arrhenius law is used, whereas for the voltage dependency an inverse power law is used. Some electronic apparatus concepts are already available to estimate in situ the DLC residual life by monitoring the temperature and voltage constraints of the application [77], DLC capacitance lifetime expectancies are displayed in Figure 11.16 as a function of the temperature for different values of the applied DC voltage. 

The double-layer capacitor is one of the electrochemical capacitors showing intermediate performances between conventional capacitors and rechargeable batteries from the viewpoint of energy and power densities. Although the terms supercapacitor and ultracapacitor are often used for double-layer capacitors, in a sense that they have higher capacitance than conventional capacitors (ceramic, film, aluminum electrolytic, or tantalum electrolytic capacitors), these terms are not to be used because they are the trademarks of certain companies products. 

Wide operational temperature range. The electrochemical capacitor must operate in the temperature range AT of at least —25° to 70°C, and its performances are closely related to the temperature characteristics of the electrolyte material. An electrolyte material satisfying the above requirements 1 through 3 at a wide temperature range is desired. 

Electrochemical capacitors, also called supercapacitors, are very attractive electricity sources because of their high power, very long durability, and intermediate energy between the classical dielectric capacitors and batteries. The performance of a typical electrochemical capacitor is based on the accumulation of charges in the electrical double layer without faradaic reactions (no electron transfer The electrons involved in double layer charging are the delocalized conduction-band electrons of the electrode material. As shown in Fig. 23.9, an electrochemical capacitor contains one positive electrode with electron deficiency and the second one with electron excess (negative). The capacitance C of one electrode due to a pure electrostatic attraction of ions is proportional to the surface area S of the electrode-electrolyte interface, according to the formula (23.3) ... 

Raymundo-Pinero, E., Khomenko, V., Frackowiak, E., and Beguin, F. (2005). Performance of manganese oxide/carbon nanotubes composites as electrode materials for electrochemical capacitors. J. Electrochem. Soc., 152, A229-A235. 

Understanding the correlation between pore size, ion size, and specific capacitance is cmcial to improving electrochemical capacitors. For example, surrounding each electrolyte ion is a layer of solvent molecules that is attracted to the charged ions (solvation layer). It has generally been assumed that the pores of the electrode material must accommodate both the ion and the solvation layer in order for the entire surface area to be accessed by the electrolyte ions. However, it has been shown that capacitance increases anomalously if the pore size is decreased below the size of the solvation shell. The capacitance increase is almost 50% compared with tire best performing commercially available activated carbons (24). 

Burke, A. 2007. R D considerations for the performance and application of electrochemical capacitors. Electrochimica Acta 53 1083—1091. 

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