Active electrode materials electrodes

The substance named first represents the positive electrode the substance named second is the negative electrode. In all cases except for air(oxygen) systems, the active electrode material is the oxide or the hydroxide of the named species. 

Perhaps the first practical application of carbonaceous materials in batteries was demonstrated in 1868 by Georges Le-clanche in cells that bear his name [20]. Coarsely ground MnO, was mixed with an equal volume of retort carbon to form the positive electrode. Carbonaceous powdered materials such as acetylene black and graphite are commonly used to enhance the conductivity of electrodes in alkaline batteries. The particle morphology plays a significant role, particularly when carbon blacks are used in batteries as an electrode additive to enhance the electronic conductivity. One of the most common carbon blacks which is used as an additive to enhance the electronic conductivity of electrodes that contain metal oxides is acetylene black. A detailed discussion on the desirable properties of acetylene black in Leclanche cells is provided by Bregazzi [21], A suitable carbon for this application should have characteristics that include (i) low resistivity in the presence of the electrolyte and active electrode material, (ii) absorption and retention of a significant... 

One can only admire the insight of the first researchers who used Ni as the active electrode material in the Ni/YSZ cermet anodes In addition to being a good electrocatalyst for the charge transfer reaction (3.8), Ni is also an excellent catalyst for the steam or C02-reforming of methane ... 

The application of PANI as active electrode material in a commercially available polymer lithium battery is described by Nakajima and Kawagoe In aprotic solvents... 

The second approach is an adaptation of the voltammetry technique to the working environment of electrolytes in an operational electrochemical device. Therefore, neat electrolyte solutions are used and the working electrodes are made of active electrode materials that would be used in an actual electrochemical device. The stability limits thus determined should more reliably describe the actual electrochemical behavior of the investigated electrolytes in real life operations, because the possible extension or contraction of the stability window, due to either various passivation processes of the electrode surface by electrolyte components or electrochemical decomposition of these components catalyzed by the electrode surfaces, would have been... 

As a compromise between the above two approaches, the third approach adopts nonactive (inert) materials as working electrodes with neat electrolyte solutions and is the most widely used voltammetry technique for the characterization of electrolytes for batteries, capacitors, and fuel cells. Its advantage is the absence of the reversible redox processes and passivations that occur with active electrode materials, and therefore, a well-defined onset or threshold current can usually be determined. However, there is still a certain arbitrariness involved in this approach in the definition of onset of decomposition, and disparities often occur for a given electrolyte system when reported by different authors Therefore, caution should be taken when electrochemical stability data from different sources are compared. 

Figure 6.8. Gibbs energy profiles of a proton discharge process resulting in a metal-hydrogen bond formation. The difference in the Gibbs energy of adsorption of hydrogen between metal 1 to metal 2 lowers the activation barrier for the discharge and makes metal 2 the electrocatalytically more favorable (active) electrode material.

Another example of a practical battery, but one less commonly used, is the Edison cell. The active electrode materials consist of iron and nickel dioxide in contact with an electrolyte consisting of aqueous potassium hydroxide solution. Owing to its marked instability, the Ni02 changes spontaneously to Ni203 with liberation of oxygen. The reactions responsible for the flow of current are as follows ... 

In modem commercial lithium-ion batteries, a variety of graphite powder and fibers, as well as carbon black, can be found as conductive additive in the positive electrode. Due to the variety of different battery formulations and chemistries which are applied, so far no standardization of materials has occurred. Every individual active electrode material and electrode formulation imposes special requirements on the conductive additive for an optimum battery performance. In addition, varying battery manufacturing processes implement differences in the electrode formulations. In this context, it is noteworthy that electrodes of lithium-ion batteries with a gelled or polymer electrolyte require the use of carbon black to attach the electrolyte to the active electrode materials.49-54 In the following, the characteristic material and battery-related properties of graphite, carbon black, and other specific carbon conductive additives are described. 

When applied as conductive additive in the positive electrode, graphite and carbon black show complementary properties which are summarized in Table 7.3. The decision which carbon type should be selected depends on the cell requirements and the type of active electrode materials used in the electrodes. The TEM pictures in Figure 7.7 compare the morphology of a typical conductive carbon black and a graphite powder and illustrate the dimensional differences of the primary particles of a factor of about 10. 

In order to satisfy the industrial demand, the performance of supercapacitors must be improved and new solutions should be proposed. The development of new materials and new concepts has enabled important breakthroughs during the last years. In this forecast, carbon plays a central role. Due to its low cost, versatility of nanotextural and structural properties, high electrical conductivity, it is the main electrode component. Nanoporous carbons are the active electrode material, whereas carbon blacks or nanotubes can be used for improving the conductivity of electrodes or as support of other active materials, e.g., oxides or electrically conducting polymers. 

Within a given line of battery technology, energy and power density typically are inversely related. Increasing the energy density requires maximization of active electrode material mass per battery mass and thus requires minimization of the amount of additional components (such as current collector, conductive additives, or void space for optimizing electronic and ionic connectivity within an electrode material, see Section 3.5.5), most of which are beneficial for increased power densities. 

Semihydrophobic electrodes are made from an active electrode material (- electrocatalyst), a binder (dissolved polymer), and a hydrophobizing agent (e.g., dispersion of polytetrafluoroethylene PTFE). Upon thorough mixing a slurry is obtained, which is spread onto a material serving as mechanical carrier and in most cases also as current collector. After removal of the solvent a porous layer/sheet is obtained. Upon contact with an aqueous electrolyte solution various interactions are possible [ii] ... 

Activated carbon nanotubes as active electrode materials... 

Cell operation requires the presence of separators which are well wetted by the electrolyte and provide good electronic insulation, high rates of lithium ion transport, and retention of active electrode material. Among materials used, the rather expensive boron nitride felt seems to be superior in terms of performance and cycle life than the much cheaper ceramic powders. 

Electrogenerated radicals can also react with other active electrode materials. Reduction of allyl bromide at a tin cathode, or ethyl bromide at lead affords the corresponding organometallic tin or lead compounds in 75% or 90% yield, respectively [177]. The anodic oxidation of ethyl magnesium bromide also generates ethyl radicals that can be trapped at a lead anode. This reaction is the basis of the NALCO process, which until recently has been used to produce tetraethyllead in a technical scale [178]. 

Lithium and sulfur are promising active electrode materials for batteries because of their low equivalent weight, low cost, and suitable electrochemical properties. The major question in the use of these active electrode materials is whether the electrodes will be able to provide sustained high performance. Until recently, capacity retention over an extended period has been difficult to achieve. 

These reactions as written, however, appear to be thermodynamically unfavorable. Therefore, stabilization of the products, S or S2", is one possible way to enhance decomposition of the intermediates. This can be accomplished by using additives with the sulfur or by using sulfur compounds as the active electrode material. In addition, using compounds... 

Reaction 15 appeared to take place in a cell using B2S3 as the active electrode material. Gas was evolved for a long time without electrochemical operation of the cell. Free energy estimates indicate that Reaction 15 was a likely cause of this gas formation. 

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