Nickel-cadmium battery construction

Rgure4 2 Chloride Alkad Unibloc nickel-cadmium battery construction (Courtesy of Chloride Batteries)... 

For alkaline storage batteries requirements are often demanded exceeding by far those for lead storage batteries. The reason is that the suitable materials for the positive electrode are very expensive (silver oxide, nickel hydroxide) and thus the use of these storage batteries is only justified where requirements as to weight, number of cycles, or temperature range prohibit other solutions. Besides a few standardized versions — mainly for nickel-cadmium batteries — this has led to the existence of a large diversity of constructions for special applications [4-6, 108, 109],... 

In 1899, the nickel-cadmium battery, the first alkaline battery, was invented by a Swedish scientist named Waldmar Jungner. The special feature of this battery was its potential to be recharged. In construction, nickel and cadmium electrodes in a potassium hydroxide solution, it was the first battery to use an alkaline electrolyte. This battery was commercialized in Sweden in 1910 and reached the Unites States in 1946. The first models were robust and had significantly better energy density than lead-acid batteries, but nevertheless, their wide use was limited because of the high costs. 

Starved electrolyte battery — A -> battery with minimum amount of -> electrolyte. The electrolyte in starved electrolyte cells or batteries exists in the porous structure of the - electrodes and absorbed in the separator, so it contains little or no free fluid electrolytic solution. This type of batteries is used in certain constructions of sealed - lead-acid and -> nickel-cadmium batteries that rely on gas diffusion and recombination on the electrodes during charging or overcharging in order to maintain maintenance-free conditions, and to suppress pressure buildup. Starved electrolyte batteries benefit from larger - energy density due to the reduced amount of electrolyte. This design may suffer from poor heat dissipation compared with -> flooded batteries, thus for high power applications this point has to be taken into account. 

Gas-proof constructions are often designed like commercial batteries (including button cells), so they can replace the primary cells in portable electric and microelectric devices. Meanwhile, usage of nickel-cadmium batteries is strongly limited by law because of the dangers related to toxic cadmium. 

Figure 10.14 The construction of a cylindrical nickel/ cadmium battery. Key A, seal By positive terminal C, cell lid D, connection to positive plate E, cell case Fy positive plate G, separator H, sintered metal foil Iy negative paste Jy connection to negative plate. Diagram supplied by Berec Ltd.

Lead-acid and nickel/cadmium batteries differ in plate design, as shown in Figure 7.4. In lead-acid batteries the type of the positive plate designates the cell type. The negative plate always is a grid plate. In traditional nickel/cadmium cells and batteries the positive and the negative plates are of the same construction. 

The voltage profile of a sealed nickel-cadmium batteries is different from the one for a vented one, as illustrated in Fig. 28.26 The end-of-charge voltage for the sealed battery is lower. The negative plate does not reach as high a state of charge as it does in the vented construction because of the oxygen recombination reaction. 

An aqueous solution of potassium hydroxide is the major component of the electrolyte. A minimum amount of electrolyte is used in this sealed cell design, with most of the Uquid absorbed by the separator and the electrodes. This starved-electrolyte design, similar to the one in sealed nickel-cadmium batteries, facilitates the diffusion of oxygen to the negative electrode at the end of the charge for the oxygen-recombination reaction. This is essentially a dry-cell construction, and the cell is capable of operating in any position. 

Sealed nickel-metal hydride cells and batteries are constructed in cylindrical, button, and prismatic configurations, similar to those used for the sealed nickel-cadmium battery. 

Fig. 11.13 The construction of a cylindrical nickel-cadmium battery. (Courtesy Berec Ltd.)...

Where a rechargeable power source is required for portable-in-use apparatus, the nickel-cadmium system is generally specified. Nickel-cadmium batteries and cells are available in a wide range of cylindrical and button sizes, and they are ideally suited to high-rate applieations. Both sintered electrode cylindrical batteries and mass plate electrode button cells constructions are available. The following discussion refers largely to the former type, since these oceupy the major part of the market. 

Figure 19.7 Eveready Sub C sealed high-rate nickel-cadmium battery with jelly roll construction (Courtesy of Union Carbide)...

Analyses of bullion lead from primary and secondary sources are given in Table 15.2. The data show that the main impurities found in secondary lead are the major constituents of the lead alloys used in the construction of the battery, namely, antimony, tin, arsenic, and copper, whilst minor contaminants include nickel, cadmium, sulfur, bismuth, and silver. 

Also secondary battery systems exhibit a broad range of different rates of selfdischarge. Their values, however, are based on a 1-month period in contrast to primary systems (1-year period). Depending on system and construction typical values vary between 2% and 30% per month at ambient temperature. For the lead-acid system the values vary between 2% and 20% per month depending on antimony content and age. The lithium-ion system offers about 5% to 10% per month. Values in the range of 20% to 30% per month are observed for the nickel cadmium and the nickel metal hydride system. 

Figure 7.5 is a general survey of the different plate types and their combination in cells of both systems. In Figure 7.6 and Figure 7.7 the most usual plate construction for lead-acid batteries are shown, in Figure 7.8 today s construction of plates for nickel/cadmium cells. 

A listing of several typical vented sintered-plate nickel-cadmium cells is given in Table 27.3. The 14-, 22-, and 36-Ah sizes are those typically employed in aircraft batteries. Other cells are available in sizes up to about 350 Ah. The larger cells are generally constructed in steel containers rather than the plastic containers now used for the aircraft-size cells. 

Sealed nickel-cadmium cells and batteries are available in several constructions. The most common types are the cylindrical shaped batteries (see Table 28.3). Smaller button batteries and rectangular batteries are also manufactured. 

Pocket Plate Electrode. This is the same type of electrode used in pocket plate nickel-cadmium and nickel-iron batteries. Electrodes are prepared by loading nickel hydroxide hydrate active material and a conductive additive (graphite and/or nickel flake) into tubular flat pockets which are then assembled into electrodes. Little interest currently exists in using this type of electrode in nickel-zinc cells since modern cells attempt to utilize lightweight electrode construction. 

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