Electrode Batteries

Adding teUurium to lead and to lead aUoyed with sUver and arsenic improves the creep strength and the charging capacity of storage battery electrodes (see Batteries). These aUoys have also been suggested for use as insoluble anodes in electrowinning. 

Activation Processes. To be useful ia battery appHcations reactions must occur at a reasonable rate. The rate or abiUty of battery electrodes to produce current is determiaed by the kinetic processes of electrode operations, not by thermodynamics, which describes the characteristics of reactions at equihbrium when the forward and reverse reaction rates are equal. Electrochemical reaction kinetics (31—35) foUow the same general considerations as those of bulk chemical reactions. Two differences are a potential drop that exists between the electrode and the solution because of the electrical double layer at the electrode iaterface and the reaction that occurs at iaterfaces that are two-dimensional rather than ia the three-dimensional bulk. 

The detailed mechanism of battery electrode reactions often involves a series of chemical and electrochemical or charge-transfer steps. Electrode reaction sequences can also include diffusion steps on the electrode surface. Because of the high activation energy required to transfer two electrons at one time, the charge-transfer reactions are beheved to occur by a series of one electron-transfer steps illustrated by the reactions of the 2inc electrode in strongly alkaline medium (41). 

Most battery electrodes are porous stmctures in which an interconnected matrix of soHd particles, consisting of both nonconductive and electronically conductive materials, is filled with electrolyte. When the active mass is nonconducting, conductive materials, usually carbon or metallic powders, are added to provide electronic contact to the active mass. The soHds occupy 50% to 70% of the volume of a typical porous battery electrode. Most battery electrode stmctures do not have a well defined planar surface but have a complex surface extending throughout the volume of the porous electrode. MacroscopicaHy, the porous electrode behaves as a homogeneous unit. 

Silver [7440-22-4] Ag, as an active material in electrodes was first used by Volta, but the first intensive study using silver as a storage battery electrode was reported in 1889 (5) using silver oxide—iron and silver oxide—copper combinations. Work on silver oxide—cadmium followed. In the 1940s, the use of a semipermeable membrane combined with limited electrolyte was introduced by Andrir in the silver oxide—2inc storage battery. 

PIa.tes, Plates are the part of the cell that ultimately become the battery electrodes. The plates consist of an electrically conductive grid pasted with a lead oxide—lead sulfate paste which is the precursor to the electrode active materials which participate in the electrochemical charge—discharge reactions. 

This section gives a brief overview of the structure of nickel hydroxide battery electrodes and a more detailed review of the solid-state chemistry and electrochemistry of the electrode materials. Emphasis is on work done since 1989. 

The Raman spectroscopic work of Ja-covitz [31], Cornilsen et al. [32, 33], and Audemer et al. [34] is the most direct spectroscopic evidence that the discharge product in battery electrodes, operating of the pi ji cycle, is different from well-crystallized / -Ni(OH)2. The O-H stretching modes and the lattice modes in the Raman spectra are different from those found for well-crystallized Ni(OH)2, prepared by recrystallization from the ammonia complex, and are more similar to those... 

In battery electrodes, the stoichiometric composition is usually not accomplished, and oxidation ends at a composition of about PbO, 9g [7]. 

The case of cerium is of particular interest. Adzic et al. [43] examined the properties of a homologous series of alloys with a composition corresponding to La1 lCerNi355Co075Mn()4Al03 and measured their comparative performance as battery electrodes. A PCT diagram for this system is shown in Fig. 10. 

Cobalt is invariably present in commercial MHt battery electrodes. It tends to increase hydride thermodynamic stability and inhibit corrosion. However, it is also expensive and substantially increases battery costs thus, the substitution of Co by a lower/cost metal is desirable. Willems and Buschow [40] attributed reduced corrosion in LaNi 5 vCoi (x= 1 -5) to low Vn. Sakai et al. [47 J noted that LaNi25Co25 was the most durable of a number of substituted LaNi5 iCoi alloys but it also had the lowest storage capacity. 

The simulated short-circuit test was developed to characterize the response of the separator to a short circuit without the complications of battery electrodes. The separator was spirally wound between lithium foils and placed in an AA-size can. To avoid lithium dendrite formation, an alternating voltage was applied to the cell. The cell current and can temperature were monitored. Figure 6 shows the behavior of Celgard membranes. 

The enormous efforts put into the basic research and development of conducting polymers are naturally related to hopes of feasible technical apphcations The starting point of this development was the discovery that PA can fimction as an active electrode in a rechargeable polymer battery. Since then, the prospects of technical application have grown considerably Apart from the battery electrode, conducting polymers are discussed as potential electrochromic displays... 

FIGURE 27.3 Spectroelectrochemical cell for in situ XRD on battery electrode materials. 

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