Electrochemical Processes in Batteries

Electrochemical Processes in Batteries Primary (Nonrechargeable) Batteries Secondary (Rechargeable) Batteries... 

The dry cell battery is a typical example of galvanic corrosion, or two metal corrosion as it is otherwise called. When two dissimilar metals are immersed in a conductive or corrosive medium, there is always the potential for a change in them. Once these metals are connected this difference induces electron flow between them. The less corrosion resistant metal is attacked more than the more resistant metal. This is an electrochemical process. In the case of a dry cell battery, the carbon electrode acts as the cathode (the more resistant materials) and zinc as the corroding anode. The natural phenomenon of corrosion is used in this case for producing electricity. 

In the remainder of this chapter, we will discuss both types of electrochemical processes. In the next section we will concern ourselves with the practical galvanic cells we know as batteries. 

In the past, electrochemical measurements of corrosion as well as processes in batteries or other electrochemical processes were averaged over many atoms and molecules. Atomic details of electron- and ion-transfer reactions associated with dissolution and passivation are now ripe for further progress given nanoscale experimental and computational advances. Recent advances such as scanning electro-... 

Abyaneh, M. and Fleischmann, M. (1991) The modelling of electrocrystaUisation processes in battery systems. Proceedings of the Electrochemical Society Conference, 91-10, 96. 

Following the possibilities for sol-gel processing in batteries and electrochromic devices, we have extended its use to other electrochemical devices and systems. Like batteries, fuel cells have many interfaces between components. There are interfaces between electrodes and current collectors, between electrodes and electrolyte and between electrodes and interconnects. More often than not, the interfaces are the location of failure in an... 

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. 

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. 

Galvanic cells in which stored chemicals can be reacted on demand to produce an electric current are termed primaiy cells. The discharging reac tion is irreversible and the contents, once exhausted, must be replaced or the cell discarded. Examples are the dry cells that activate small appliances. In some galvanic cells (called secondaiy cells), however, the reaction is reversible that is, application of an elec trical potential across the electrodes in the opposite direc tion will restore the reactants to their high-enthalpy state. Examples are rechargeable batteries for household appliances, automobiles, and many industrial applications. Electrolytic cells are the reactors upon which the electrochemical process, elec troplating, and electrowinning industries are based. 

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