Button cells

The titanium sulfide is able to act as a lithium reservoir. On iatercalation with lithium, the titanium lattice expands from ca 570 to 620 pm as the iatercalation proceeds to completion on formation of TiI iS2. Small button cells have been developed, incorporating lithium perchlorate ia propyleae carboaate electrolyte, for use ia watches and pocket calculators (see Batteries). 

Almost all the methods described for the nickel electrode have been used to fabricate cadmium electrodes. However, because cadmium, cadmium oxide [1306-19-0], CdO, and cadmium hydroxide [21041-95-2], Cd(OH)2, are more electrically conductive than the nickel hydroxides, it is possible to make simple pressed cadmium electrodes using less substrate (see Cadmium and cadmium alloys Cadmium compounds). These are commonly used in button cells. 

Other Cells. Other methods to fabricate nickel—cadmium cell electrodes include those for the button cell, used for calculators and other electronic de dces. Tliis cell, the construction of which is illustrated in Figure is commonly made using a pressed powder nickel electrode mixed with graphite that is similar to a pocket electrode. Tlie cadmium electrode is made in a similar manner. Tlie active material, graphite blends for the nickel electrode, are ahnost the same as that used for pocket electrodes, ie, 18% graphite. 

Coin and Button Cell Commercial Systems. Initial commercialization of rechargeable lithium technology has been through the introduction of coin or button cells. The eadiest of these systems was the Li—C system commercialized by Matsushita Electric Industries (MEI) in 1985 (26,27). The negative electrode consists of a lithium alloy and the positive electrode consists of activated carbon [7440-44-0J, carbon black, and binder. The discharge curve is not flat, but rather slopes from about 3 V to 1.5 V in a manner similar to a capacitor. Use of lithium alloy circumvents problems with cycle life, dendrite formation, and safety. However, the system suffers from generally low energy density. 

As of this writing, there is Httle commercialization of advanced battery systems. Small rechargeable lithium button cells have been commercialized, however, by Sanyo, Matsushita (Panasonic), and Toshiba. These cells are intended for original equipment manufacturer (OEM) use in appHcations such as memory backup and are not available to the general consumer. 

The button cells that provide the energy for watches, electronic calculators, hearing aids, and pacemakers are commonly alkaline systems of the silver oxide-zinc or mercuric oxide-zinc variety. These alkaline systems provide a vei y high energy density, approximately four times greater than that of the alkaline zinc-manganese dioxide battery. 

The capacity of single-use alkaline zinc-air cells is twice that of manganese dioxide-zinc cells. They cost less than silver oxide-Zn batteries or Li batteries. The best example of consumer usage is the hearing-aid button cell. In sealed condition it can be... 

It is so universally applied that it may be found in combination with metal oxide cathodes (e.g., HgO, AgO, NiOOH, Mn02), with catalytically active oxygen electrodes, and with inert cathodes using aqueous halide or ferricyanide solutions as active materials ("zinc-flow" or "redox" batteries). The cell (battery) sizes vary from small button cells for hearing aids or watches up to kilowatt-hour modules for electric vehicles (electrotraction). Primary and storage batteries exist in all categories except that of flow-batteries, where only storage types are found. Acidic, neutral, and alkaline electrolytes are used as well. The (simplified) half-cell reaction for the zinc electrode is the same in all electrolytes ... 

Cells of cylindrical geometry are produced mainly in four sizes D (LR-20), C (LR-14), AA (LR-6), and AAA (LR-03). The two other alkaline cells in this section (using HgO or an oxygen electrode as cathode) are almost exclusively produced as small button cells. 

Mechanical strength becomes an important criterion, because wound cells (spiral-type construction), in which a layer of separator material is spirally wound between each two electrodes, are manufactured automatically at very high speed. Melt-blown polypropylene fleeces, with their excellent tensile properties, offer an interesting option. Frequently two layers of the same or different materials are used, to gain increased protection against shorts for button cells the use of three layers, even, is not unusual. Nevertheless the total thickness of the separation does not exceed 0.2 - 0.3 mm. For higher-temperature applications (up to about 60 °C) polypropylene fleeces are preferred since they offer a better chemical stability, though at lower electrolyte absorption [ 114"]. 

Zinc-silver oxide batteries as primary cells are known both as button cells, e.g., for hearing aids, watches, or cameras, and for military applications, usually as reserve batteries. Since the latter after activation have only a very short life (a few seconds to some minutes), a separation by cellulo-sic paper is generally sufficient. 

This section reviews the state-of-the-art in battery separator technology for lithium-ion cells, with a focus on separators for spirally wound batteries in particular, button cells are not considered. 

Button cells consist of cathode and anode cans (used as the terminals), powdered zinc anode, containing gelled electrolyte and the corrosion inhibitor, separator with electrolyte, thin (0.5 mm) carbon cathode with catalyst and PTFE, waterproof gas-permeable (teflon) layer and air distribution layer for the even air assess over the cathode surface. Parameters of battery depend on the air transfer rate, which is determined by quantity and diameters of air access holes or porosity of the gas-diffusion membrane. Air-zinc batteries at low rate (J=0,002-0,01C at the idle drain and J= 0,02-0,04C at the peak continuous current) have flat discharge curves (typical curve is shown by Figure 1). 

FIGURE 2.28 Voltage drop due to sulfur poisoning versus CO concentration for an SOFC button cell operated on a HrCO fuel mixture containing 5 ppm H2S at 1000°C with current density of 200 mA/cm2. (From Sasaki, K. et al., Proceedings of the Ninth International Symposium on Solid Oxide Fuel Cells, 2005-07 1267-1275. Reproduced by permission of ECS-The Electrochemical Society.)... 

Sprenkle et al. [73] Single anode-supported button cell 750... 

To develop an alternative MIEC cathode not only the ex situ properties, e.g., cr, TEC, /), and k, but also the electrocatalytic activity, structural and chemical stability, and Cr-tolerance must be considered. Beyond testing in small SOFC button cells, the viability of new cathode materials must ultimately be proven in large-scale stack cells under practical current and temperature gradients. The issues involved in the development of cathode materials for large-scale stacks are significantly more complex than those in the small button cells briefly reviewed in this chapter. However, this does provide serious challenges as well as opportunities for materials scientists and engineers in the development of commercially viable ITSOFCs. 

FIGURE 5.12 Photograph of a zirconia button cell sealed to a zirconia tube. 

The main applications of Zn—Ag20 cells are button cells for watches, pocket calculators, and similar devices. The cell operates with an alkaline electrolyte. The Zn electrode operates as discussed, whereas the Ag20 electrode follows a displacement reaction path (cf. Figure ISA). 

The ready reversibility of lithium in titanium disulfide has permitted deep cycling for close to 1000 cycles with minimal capacity loss, less than 0.05% per cycle, with excess lithium anodes. Exxon marketed button cells with LiAl anodes and TiS2 cathodes for watches and other small devices in 1977—1979 the LiAl anode improved the safety of the cells. Some of the largest lithium single cells built to date are those exhibited by Exxon at the Electric Vehicle Show in Chicago in 1977, shown in Eigure 3. 

Figure 1. Typical battery configurations (a) button cell (b) stack lead acid (c) spiral wound cylindrical lithium ion (d) spiral wound prismatic lithium-ion.

Nonwoven materials have also been developed for lithium-ion cells but have not been widely accepted, in part due to the difficulty in fabricating thin materials with good uniformity and high strength. Nonwoven separators have been used in button cells and bobbin cells when thicker separators and low discharge rates are acceptable. 

Nickel(lll) oxide, prepared from a nickel(ii) salt and sodium hypochlorite, is used for the oxidation of alkanols in aqueous alkali [46]. Residual nickel(Ii) oxide can be re-activated by reaction with sodium hypochlorite. Nickel oxides have also long been used in the manufacture of the positive pole in the Edison nickel-iron rechargeable battery, now largely superseded by die lead-acid accumulator, and in the Jungner nickel-cadmium batteries used as button cells for calculators [47]. Here, prepared nickel oxide is pressed into a holding plate of perforated nickel. Such prepared plates of nickel(lli) oxide have been proposed as reagent for the oxidation, in alkaline solution, of secondary alcohols to ketones and primary alcohols to carboxylic acids [48]. Used plates can be regenerated by anodic oxidation. 

V, depending on the reaction at the positive electrode. Applications are practically limited to small button cells [348]. 

The silver oxide and mercuric oxide button cells used in cameras and other devices requiring a miniature source of EMF consist of a zinc disk, which serves as the anode, and, on the other side of a porous separator, a paste of Ag20 or HgO. The reaction products are zinc hydroxide and metallic silver or mercury. Inert metal caps serve as the current collectors. 

Miniature batteries based on aqueous, non-aqueous and solid electrolytes are manufactured as power sources for microelectronics and other miniaturized equipment. In Fig. 1.2, the sizes and shapes of some representative button cells are shown. A typical application for such cells is in the electric watch, where the oscillator circuit draws a continuous current of 0.2-0.6 pA and depending on the type of frequency divider and display, the complete unit may require a total of up to 0.5-2.0 pA for operation. Hence the total amount of electrical energy consumed in driving the watch for a year is in the range 15-60 mWh. At present, batteries are manufactured which last for 5-10 years. Watch batteries must have exceptionally low self-discharge rates and very reliable seals to prevent leakage. Further, they... 

Fig. 1.2 Dimensions (in mm) and capacities of some representative button cells...

In Scotland, the cost of domestic mains electricity is 0.0713/kWh (in 1997). A D-size Leclanchd cell, delivering say 5 Wh, currently retails at 0.50. Thus, energy from the primary battery costs I00/kWh - a factor of over 1000 more expensive. For a 150 mWh zinc-silver oxide button cell, retailing at 1.50, the cost of energy is over 10 000/kWh ... 

The alkaline manganese dioxide cell is most widely available either as standard sized cylindrical cells with capacities ranging from 0.6 to 22 Ah or as button cells. Batteries having a wide variety of capacities and voltages are also readily available. These are all interchangeable with Leclanche and zinc chloride cells. 

Fig. 3.24 Cross-section of a typical zinc-mercuric oxide button cell...

The cross-section of a typical mercury button cell is shown in Fig. 3.24. The cathode and anode current collectors are the steel case and steel top, respectively. Attention is drawn to the sophisticated engineering design of this cell, which has provision for automatic venting of any pressure caused by hydrogen evolution, with any electrolyte displaced being absorbed in the safety sleeve between the inner and outer case. 

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