Supercapacitor conductivity

From a physical point of view, heat transfer has its origins in temperature differences. Thus, a transfer of energy in the form of heat occurs any time that a temperature gradient exists within a system, or when two systems at different temperatures come into contact. There are three modes of heat transfer for a supercapacitor heat conduction, heat convection and radiation. Inside the supercapacitor, conduction is the dominant mode of heat transfer therefore, to begin with, we can discount the other two modes of heat transfer. However, it is helpful to take account of convective heat transfer between the ambient air and the outer surface of the supercapacitor. 

Conducting polymers have found applications in a wide variety of areas,44 45 and many more have been proposed. From an electrochemical perspective, the most important applications46 appear to be in batteries and supercapacitors 47,48 electroanalysis and sensors49-51 electrocatalysis,12,1, 52 display and electrochromic devices,46 and electromechanical actuators.53... 

A classic definition of electrochemical ultracapacitors or supercapacitors summarizes them as devices, which store electrical energy via charge in the electrical double layer, mainly by electrostatic forces, without phase transformation in the electrode materials. Most commercially available capacitors consist of two high surface area carbon electrodes with graphitic or soot-like material as electrical conductivity enhancement additives. Chapter 1 of this volume contains seven papers with overview presentations, and development reports, as related to new carbon materials for this emerging segment of the energy market. 

In the third paper by French and Ukrainian scientists (Khomenko et al.), the authors focus on high performance a-MnCVcarbon nanotube composites as pseudo-capacitor materials. Somewhat surprisingly, this paper teaches to use carbon nanotubes for the role of conductive additives, thus suggesting an alternative to the carbon blacks and graphite materials - low cost, widely accepted conductive diluents, which are typically used in todays supercapacitors. The electrochemical devices used in the report are full symmetric and optimized asymmetric systems, and are discussed here... 

In supercapacitors, apart from the electrostatic attraction of ions in the electrode/electrolyte interface, which is strongly affected by the electrochemically available surface area, pseudocapacitance effects connected with faradaic reactions take place. Pseudocapacitance may be realized through carbon modification by conducting polymers [4-7], transition metal oxides [8-10] and special doping via the presence of heteroatoms, e.g. oxygen and/or nitrogen [11, 12]. 

The present work describes the results of investigations of carbon materials used by us for creation of conductive skeletons in the EC electrode body. Investigations were carried out in full-size Ni Oxide and carbon-carbon supercapacitor systems with aqueous solution of KOH. 

Electronically conducting polymers (ECPs) such as polyaniline (PANI), polypyrrole (PPy) and po 1 y(3.4-cthy 1 cncdi oxyth iophcnc) (PEDOT) have been applied in supercapacitors, due to their excellent electrochemical properties and lower cost than other ECPs. We demonstrated that multi-walled carbon nanotubes (CNTs) prepared by catalytic decomposition of acetylene in a solid solution are very effective conductivity additives in composite materials based on ECPs. In this paper, we show that a successful application of ECPs in supercapacitor technologies could be possible only in an asymmetric configuration, i.e. with electrodes of different nature. 

Mastragostino M., Arbizzani C., Soavi F. Conducting polymers as electrode materials in supercapacitors. Solid State Ionics 2002 148 493-8. 

V. Khomenko, E. Frackowiak, V. Barsukov, F. Beguin. Development of supercapacitors based on conducting polymers. This book 2005. 

Yu, G., et ah, Enhancing the supercapacitor performance ofgraphene/Mn02nanostructured electrodes by conductive wrapping. Nano Letters, 2011.11(10) p. 4438-4442. 

Carbon nanotubes can be employed either as electrode materials or conductive fillers for the active materials in various electrochemical energy-storage systems [20]. For energy generation and storage, nanotubes hold promise as supercapacitors. 

An electrochemical capacitor is a device that stores electrical energy in the electrical double layer that forms at the interface between an electrolytic solution and an electronic conductor. The term applies to charged carbon—carbon systems as well as carbon-battery electrode and conducting polymer electrode combinations sometimes called ultracapacitors, supercapacitors, or hybrid capacitors. 

Energy Storage—CNTs have a very high surface area (about 10 m /g), good electrical conductivity and can be made very linear (straight). They have been used to make lithium batteries with the highest reversible capacity of any carbon material and employed to make supercapacitor electrodes. CNTs are used in a variety of fuel cell applications where durability is important. 

A typical configuration of a double-layer supercapacitor involves two metallic collectors which hold in place the carbon powder electrodes, which in turn are separated by an electrolyte, in most of the cases formed by liquid solutions (Fig. 9.28.) A layer of porous, non-conductive material acts as a separator. 

Solid ionic conductors can also be used in the fabrication of solid state double-layer supercapacitors. An example is the device developed in the late 1960s by Gould Ionics which adopted a cell system using a silver-carbon electrode couple separated by the highly ionically conducting solid electrolyte RbAg4I5 (see Section 9.1) ... 

The synthesis of nanostructured carbon using aliphatic alcohols as selfassembling molecules has demonstrated that this strategy can be extended beyond metal oxide-based materials [38]. Recently, we have reported the synthesis of a novel carbon material with tunable porosity by using a liquid-crystalline precursor containing a surfactant and a carbon-yielding chemical, furfuryl alcohol. The carbonization of the cured self-assembled carbon precursor produces a new carbon material with both controlled porosity and electrical conductivity. The unique combination of both features is advantageous for many relevant applications. For example, when tested as a supercapacitor electrode, specific capacitances over 120 F/g were obtained without the need to use binders, additives, or activation to increase surface area [38]. The proposed synthesis method is versatile and economically attractive, and allows for the precise control of the structure. 

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