Electrochemical systems batteries

Figure 25.1 gives an overview of aU the computational tools available to model and simulate batteries, electrochemical systems, and materials at various length and time scales. The models used at various scales can be summarized as ... 

The lead—acid battery is one of the most successful electrochemical systems and the most successful storage battery developed. In 1988 total battery sales, excluding Eastern European central economy countries, were more than 17 biUion (1). Lead—acid battery sales accounted for about 57% of that figure. About 80% of the lead [7439-92-1] (qv), Pb, consumption in the United States was for batteries in that year. 

An excellent review covers the charge and discharge processes in detail (30) and ongoing research on lead—acid batteries may be found in two symposia proceedings (32,33). Detailed studies of the kinetics and mechanisms of lead —acid battery reactions are pubUshed continually (34). Although many questions concerning the exact nature of the reactions remain unanswered, the experimental data on the lead—acid cell are more complete than for most other electrochemical systems. 

Electrochemical systems convert chemical and electrical energy through charge-transfer reactions. These reactions occur at the interface between two phases. Consequendy, an electrochemical ceU contains multiple phases, and surface phenomena are important. Electrochemical processes are sometimes divided into two categories electrolytic, where energy is supplied to the system, eg, the electrolysis of water and the production of aluminum and galvanic, where electrical energy is obtained from the system, eg, batteries (qv) and fuel cells (qv). 

The industrial economy depends heavily on electrochemical processes. Electrochemical systems have inherent advantages such as ambient temperature operation, easily controlled reaction rates, and minimal environmental impact (qv). Electrosynthesis is used in a number of commercial processes. Batteries and fuel cells, used for the interconversion and storage of energy, are not limited by the Carnot efficiency of thermal devices. Corrosion, another electrochemical process, is estimated to cost hundreds of millions of dollars aimuaUy in the United States alone (see Corrosion and CORROSION control). Electrochemical systems can be described using the fundamental principles of thermodynamics, kinetics, and transport phenomena. 

Electrochemical systems are found in a number of industrial processes. In addition to the subsequent discussions of electrosynthesis, electrochemical techniques are used to measure transport and kinetic properties of systems (see Electroanalyticaltechniques) to provide energy (see Batteries Euel cells) and to produce materials (see Electroplating). Electrochemistry can also play a destmctive role (see Corrosion and corrosion control). The fundamentals necessary to analyze most electrochemical systems have been presented. More details of the fundamentals of electrochemistry are contained in the general references. 

V. Barsukov, F. Beck, New Promising Electrochemical Systems for Rechargeable Batteries, Kluwer Academic Publishers, Dordrecht, 1996. 

The presence of polymer, solvent, and ionic components in conducting polymers reminds one of the composition of the materials chosen by nature to produce muscles, neurons, and skin in living creatures. We will describe here some devices ready for commercial applications, such as artificial muscles, smart windows, or smart membranes other industrial products such as polymeric batteries or smart mirrors and processes and devices under development, such as biocompatible nervous system interfaces, smart membranes, and electron-ion transducers, all of them based on the electrochemical behavior of electrodes that are three dimensional at the molecular level. During the discussion we will emphasize the analogies between these electrochemical systems and analogous biological systems. Our aim is to introduce an electrochemistry for conducting polymers, and by extension, for any electrodic process where the structure of the electrode is taken into account. 

As noted earlier, the kinetics of electrochemical processes are inflnenced by the microstractnre of the electrolyte in the electrode boundary layer. This zone is populated by a large number of species, including the solvent, reactants, intermediates, ions, inhibitors, promoters, and imparities. The way in which these species interact with each other is poorly understood. Major improvements in the performance of batteries, electrodeposition systems, and electroorganic synthesis cells, as well as other electrochemical processes, conld be achieved through a detailed understanding of boundaiy layer stracture. 

Electrochemical systems with reacting metal electrodes are widely used in batteries, electrometallurgy, electroplating, and other areas. Corrosion of metals is a typical example of processes occurring at reacting metal electrodes. 

Comparative Characteristics Often, the electric and other characteristics of batteries differing in size, design, or electrochemical system need to be compared. The easiest way is by using normalized (reduced) parameters. Thus, current density serves as a measure of the relative reaction rate. Therefore, plots of voltage vs. current density provide a useful characterization of a battery, reflecting its specific properties independent of its size. 

In subsequent sections we provide brief information on batteries of various electrochemical systems. The major electrochemical features of each type will be pointed out. The relative discharge characteristics of batteries of the various systems are shown in Fig. 19.4 as a Ragone plot of w vs. p. For specific details of design and manufacturing technology, as well as for more details on performance and characterization, battery books and monographs should be consulted. 

In topochemical reactions all steps, including that of nucleation of the new phase, occur exclusively at the interface between two solid phases, one being the reactant and the other the product. As the reaction proceeds, this interface gradually advances in the direction of the reactant. In electrochemical systems, topochemical reactions are possible only when the reactant or product is porous enough to enable access of reacting species from the solution to each reaction site. The number of examples electrochemical reactions known to follow a truly topochemical mechanism is very limited. One of these examples are the reactions occurring at the silver (positive) electrode of silver-zinc storage batteries (with alkaline electrolyte) ... 

The last paper in this chapter is by Professor N. Korovin of Moscow Power Engineering Institute, Russian Federation. The author could not attend the NATO-CARWC in Chicago due to a last minute cancellation. His work, contributed to this volume is a comprehensive overview of various metal-air battery technologies, with a heavy focus on the role of carbon materials in these electrochemical systems. 

The main characteristics of cylindrical AAA size metal-air batteries with PANI/TEG catalysts, as well as standard Zn-Mn02 battery have been gathered in the Table 5. Realization of all types of batteries in the same AAA size gives the possibilities for comparison of above electrochemical systems for some applications. 

The specific characteristics (such as Ah/kg and Ah/1) of the metal-air batteries is significantly higher than that of the classical electrochemical systems with the same metal anode. 

Korovin N.V. Advanced half-gas systems for rechargeable batteries . In New Promising Electrochemical Systems for Rechargeable Batteries (NPESRB), V.Z. Barsukov, F. Beck, ed. Dordrecht Kluver Academic Publisher. 1996 171-180. 

A number of oxides with the fluorite structure are used in solid-state electrochemical systems. They have formulas A02 xCaO or A02 xM203, where A is typically Zr, Hf, and Th, and M is usually La, Sm, Y, Yb, or Sc. Calcia-stabilized zirconia, ZrC)2.xCaO, typifies the group. The technological importance of these materials lies in the fact that they are fast ion conductors for oxygen ions at moderate temperatures and are stable to high temperatures. This property is enhanced by the fact that there is negligible cation diffusion or electronic conductivity in these materials, which makes them ideal for use in a diverse variety of batteries and sensors. 

Many advances have been made in battery technology in recent years, both through continued improvement of specific electrochemical systems and through the development and introduction of new... 

Very little work (relative to research of electrode materials and electrolytes) is directed toward characterizing and developing new separators. Similarly, not much attention has been given to separators in publications reviewing batteries.A number of reviews on the on cell fabrication, their performance, and application in real life have appeared in recent years, but none have discussed separators in detail. Recently a few reviews have been published in both English and Japanese which discuss different types of separators for various batteries. A detailed review of lead-acid and lithium-ion (li-ion) battery separators was published by Boehnstedt and Spot-nitz, respectively, in the Handbook of Battery Materials. Earlier Kinoshita et al. had done a survey of different types of membranes/separators used in different electrochemical systems, including batteries."... 

Although in principle batteries can power any device that runs on electricity, in many cases the amount of electricity would require an excessive number of batteries. Another problem is that batteries have a limited life or, in the case of rechargeable batteries, require frequent recharging. But imagine an electrochemical system in which the reactants continually flowed in the cell. The consumed reactants are replaced as the reaction proceeds, so the cell can function continuously with no need for recharging. In this situation, the flowing reactants can be considered as the fuel, and the cell is known as a fuel cell. 

By far the largest sector of the battery industry worldwide is based on the lead-acid aqueous cell whose dominance is due to a combination of low cost, versatility and the excellent reversibility of the electrochemical system, Lead-acid cells have extensive use both as portable power sources for vehicle service and traction, and in stationary applications ranging from small emergency supplies to load levelling systems. In terms of sales, the lead-acid battery occupies over 50% of the entire primary and secondary market, with an estimated value of 100 billion per annum before retail mark-up. 

J. S. Newman, Electrochemical Systems, Prentice-Hall, Englewood Cliffs, NJ, 1991 A. J. Bard and L. R. Faulkner, Electrochemical Methods. Fundamentals and Applications, John Wiley and Sons, New York, 1980 J. O M. Bockris and S. Srinivasan, Fuel Cells Their Electrochemistry, McGraw-Hill Book Company, New York, 1969 J. O M. Bockris and A. K. V. Reddy, Modern Electrochemistry, Plenum Press, New York, 1970 C. Julien, G. A. Nazri, Solid State Batteries, Kluwer Academic Publishers, Norwell, 1994 M. Winter, J. 0. Besenhard, M. E. Spahr, and P. Novak, Adv. Mater. 10 (1998) 725 F. von Sturm, Elektrochemische Stromerzeugung, VCH, Weinheim, 1969 K. J. Vetter, Electrochemical Kinetics, Academic Press, New York, 1967. 

The performance of electrochemical systems is compared in a Ragone plot (Figure 8.4). Supercapacitors have a higher power density than any battery by contrast, their energy density is much lower. The main research effort is now oriented to improving the energy. 

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