Double-layer capacitors electrolyte characteristics

Lust, E., Janes, A., and Arulepp, M. Influence of electrolyte characteristics on the electrochemical parameters of electrical double layer capacitors. J. Solid State Electr., 8, 2004 488-496. 

It is most convenient to use Ragone diagrams for the comparison of the main characteristics of electrochemical devices. Figure 30.1 shows a Ragone diagram for diverse commercial electrochemical devices conventional electrolytic capacitors, electrochemical supercapacitors (ECSCs), batteries, and fuel cells (Pandolfo and Hollenkamp, 2006). One should point out that it is mainly electric double-layer capacitors (EDLCs) of all the available ECSC types that are produced at present. 

Nambu, N., R. Takahashi, M. Takehara, M. Ue, and Y. Sasaki. 2013. Electrolytic characteristics of fluoroethylene carbonate for electric double-layer capacitors at high concentrations of electrolyte. Electrochemistry 81 817—819. 

Murayama, L, N. Yoshimoto, M. Egashira, M. Morita, Y. Kobayashi, and M. Ishikawa. 2005. Characteristics of electric double layer capacitors with an ionic liquid electrolyte containing Li ion. Electrochemistry 73 600-602. 

Pahn et al. [34] employed the CV method to investigate the effect of the concentration of the addition of l-butyl-3-methylimidazolium tetrafluoroborate ([BMIM] [BFJ) in l-ethyl-3-methylimidazolium tetrafluoroborate ([EMIM][BF4]) electrolyte on the electrochemical characteristics for electrical double-layer capacitors (EDLCs). They found the concentration of [BM1M][BF4] has little influence on the... 

The first attempts to achieve such a device were made in the 1970s. The cell had a non-symmetric Ag/RbAg4l5/C structure with a double-layer capacitance at the carbon electrode in the range of 10-40 nF cm" interface area However, due to the redox reaction, the working voltage was too low (<0.7 V) for the electronic devices of the time. Furthermore, the reversibility of the Ag electrode was poor and it was difficult to use fully the surface area of the ultrafine carbon. More recently, double-layer capacitors using acidic solution (H2SO4) as liquid electrolyte were developed by NEC (Nippon Electric Co. Ltd). A liquid electrolyte allows most of the surface area of the carbon electrode to be used. The electrical characteristics of the devices can be classified in relation to the properties of each material as follows. 

Wada H, Yoshikawa K, Eurukawa N, Inoue H, Sugoh N, Iwasaki H, Iwakura C (2006) Electrochemical characteristics of new electric double layer capacitor with acidic polymer hydrogel electrolyte. J Power Sources 159 1464... 

Although simple impedance measurement can tell the existence of an anodic film, electrochemical impedance spectroscopy (EIS) can obtain more information about the electrochemical processes. In general, the anode/electrolyte interface consists of an anodic film (under mass transport limited conditions) and a diffuse mobile layer (anion concentrated), as illustrated in Fig. 10.13a. The anodic film can be a salt film or a cation (e.g., Cu ) concentrated layer. The two layers double layer) behave like a capacitor under AC electric field. The diffuse mobile layer can move toward or away from anode depending on the characteristics of the anode potential. The electrical behavior of the anode/electrolyte interface structure can be characterized by an equivalent circuit as shown in Fig. 10.13. Impedance of the circuit may be expressed as... 

Electrochemical Supercapacitors and Hybrid Systems describes electrochemical energy storage devices having higher energy density than electrolytic capacitors and higher power density than batteries. These devices rely on the characteristics of the electrical double layer that forms on all polarized conductors when immersed in an electrolyte. The double layer forms in less than 10 s and responds to changes in a similar time frame. This is about 1,000 times faster than an electrochemical... 

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