Supercapacitors
An electric double-layer capacitor (EDLC), also known as supercapacitor, supercondenser, pseudocapacitor, electrochemical double layer capacitor, or ultracapacitor, is an electrochemical capacitor with relatively high energy density. Compared to conventional electrolytic capacitors the energy density is typically on the order of hundreds of times greater. In comparison with conventional batteries or fuel cells, EDLCs also have a much higher power density.
A typical D-cell sized electrolytic capacitor displays capacitance in the range of tens of millifarads. The same size EDLC might reach several farads, an improvement of two orders of magnitude. EDLCs usually yield a lower working voltage; as of 2010 larger double-layer capacitors have capacities up to 5,000 farads. Also in 2010, the highest available EDLC energy density is 30 Wh/kg (0.1 MJ/kg) (although 85 Wh/kg has been achieved at room temperature in the lab), lower than rapid-charging lithium-titanate batteries.
EDLCs have a variety of commercial applications, notably in "energy smoothing" and momentary-load devices. They have applications as energy-storage devices used in vehicles, and for smaller applications like home solar energy systems where extremely fast charging is a valuable feature.
(Wikipedia, Supercapacitors, 7/28/2011)
Conventional electrode materials for supercapacitors are based on nanoscaled structures with large surface areas or porosities. [Xie et al, (1234–1240) Journal of Polymer Science B: Polymer Physics 49, #17 (2011)]
Recent Journal Articles
Composite films prepared by immersion deposition of manganese oxide in carbon nanotubes grown on graphite for supercapacitors
(7328-7334) Journal of Materials Science 46 #22 (2011)
Li and Lafdi of the University of Dayton, Ohio, prepared manganese oxide/carbon nanotube (CNT) composite films on graphite by growing CNTs on the substrate using chemical vapor deposition (CVD), followed by immersion in an aqueous solution of potassium permanganate. The CVD growth created favorable conditions for deposition of the oxide on the electrode, and an aligned porous structure of the composite films, which originated from the CNT growth, could be managed. Electrochemical behaviors of the CNT and the composite films for supercapacitors were studied in 1 M Na2SO4 solution. While the oxide deposition in the CNT films was identified as contributing to capacitance enhancement, it was also found that a mild heat treatment could improve performance of the composite films. (RDC 8/23/2011)
Supercapacitive energy storage based on ion-conducting channels in hydrophilized organic network
(1234–1240) Journal of Polymer Science B: Polymer Physics 49, #17 (2011)
Xie et al of the National University of Singapore, China, developed a new electrode material, the so-called hydrophilized polymer network. The network allows for high capacitance (up to 400 F/g) energy storage in a simple film configuration without the need of high-surface-area nanostructures. It is unstable in water, but becomes extremely stable in electrolyte with high ionic strength. The above features are related to the hydrophilizing groups in the network which not only generate hydrated ionic conduction channels, but also enable the cross-linking of the network in electrolyte. Because of its practical advantages such as easy preparation and intrinsic stability in electrolyte, the hydrophilized network may provide a new route to high-performance supercapacitive energy storage. (RDC 7/27/2011)
Review Articles
Electric Double-Layer Capacitance of Inverse Opal Carbon Prepared Through Carbonization of Poly(Furfuryl Alcohol) in Contact with Polymer Gel Electrolyte Containing Ionic Liquid
( 1254–1260)Polymers for Advanced Technologies 22 #8 (2011)
Isshiki et al of Yokohama National University, Japan, prepared three-dimensionally periodic porous carbon membranes through the carbonization of poly(furfuryl alcohol) in the void spaces of opal materials consisting of monodispersed silica particles. Inverse opal carbon (IOC) membranes are obtained by the removal of silica templates. The obtained IOCs have three-dimensionally ordered macroporous structures and large specific surface areas due to the mesopores that are formed during the carbonization of the polymer precursor. IOC with three-dimensionally ordered 50-nm pores exhibits a large gravimetric capacitance of 120 F g−1, as determined by using an ionic liquid electrolyte, 1-ethyl-3-methylimidazolium bis(trifluoromethane sulfonyl)amide ([C2mim][NTf2]); this capacitance is higher than that of conventional activated carbon. Furthermore, the combination of IOC and an ion gel electrolyte, consisting of network poly(methyl methacrylate) and [C2mim][NTf2], is demonstrated to be effective for achieving a solid-state, nonvolatile, and high-capacity electric double-layer capacitor. Moreover, because of the high ionic conductivity of the ion gel and the continuous ion-conduction path through the IOC membrane, the IOCs exhibit a large specific capacitance of 100 F g−1 and a good rate capability, even at room temperature. (RDC 7/29/2011)