Pocket plate nickel/cadmium batteries

The positive and negative electrodes of pocket-plate nickel-cadmium batteries are made using the same basic design to hold the active materials. The pocket plates are buUt up of flat pockets of perforated steel strips holding the active materials. The thin steel strips are perforated by hardened steel needles or by a technique using profiled roller dies. The specific hole area is between 15 and 30%. The strips are nickel-plated to prevent iron poisoning of the positive active material. 

Pocket-plate nickel-cadmium batteries can be used at temperatures down to -20°C with the standard electrolyte. Cells filled with a more concentrated electrolyte can be used down to -50°C. Figure 26.9 shows the effect of temperature on the relative performance of a nickel-cadmium medium-rate battery with standard electrolyte. 

The memory effect—the tendency of a battery to adjust its electrical properties to a certain duty cycle to which it has been subjected for an extended period of time—has been a problem with nickel-cadmium batteries in some applications. Pocket, fiber, and plastic-bonded plate cells do not show this tendency. See Sec. 27.7.2 for a description of the memory effect with sintered-plate nickel-cadmium batteries. 

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. 

Fig. 6.1 Sequence of operations in fabrication of pocket plates for nickel-cadmium batteries. (a -(c) Formation of channels in nickel-plated perforated steel snip, (d)-(f) Filling and crimping to form a long continuous pocket, (g)-(h) Interlacing of filled strips and compression to form final plate...

FIGURE 26.7 Charge and discharge characteristics of nickel-cadmium batteries at 25°C. (a) Pocket plate battery, high rate, (b) Plastic-bonded plate battery, high rate. 

Fig. 11.11 Procedure for the manufacture of pocket-plate electrodes for a nickel-cadmium battery.

Figure19.10 Design of the pocket plate in large vented nickel-cadmium battery. Pocket plate with perforated upper and lower tap (Courtesyof Chloride Batteries)...

The aetive material of most modem types of nickel-cadmium battery is enelosed in pockets of peiTorated steel strips, whieh are joined to the plate materials. The steel strips, whieh form the walls of the pockets, are perforated from both the inside and the outside. This double perforation ereates a maximum surface area which makes for high output performance. This means that nickel-eadmium batteries can supply up to three times as much current in proportion to their nominal capacity as is normal for lead—acid batteries. 

Although one of the most common storage batteries is called the nickel/cadmium system ( NiCad ), correctly written (-)Cd/KOH/NiO(OH)(+), cadmium is not usually applied as a metal to form a battery anode. The same can be said with regard to the silver/cadmium [(-) Cd / KOH / AgO (+)] and the MerCad battery [(-)Cd/KOH/HgO(+)]. The metallic negative in these cases may be formed starting with cadmium hydroxide, incorporated in the pore system of a sintered nickel plate or pressed upon a nickel-plated steel current collector (pocket plates), which is subsequently converted to cadmium metal by electrochemical reduction inside the cell (type AB2C2). This operation is done by the customers when they start the application of these (storage)... 

Together, the annual output of the 2 factories is over 700 tonnes of cadmium metal of a purity of 99.99 % by weight and more than 650 tonnes of nickel in the form of iron nickel residues (1,900 tonnes) or ferro-nickel. The balance is made of plastic materials (cases of the industrial batteries, plastic shells around the power packs etc.), of scrap iron (metallic cases of the industrial batteries, iron residues coming form the distillation of negative pocket plates). These products are valorised at a market value either for energy production or scrap. 

Figure 10.13 A cutaway diagram of a nickel/cadmium pocket plate battery. The battery shown has a nominal capacity of 100 A h. Photograph supplied by Chloride Alcad Ltd.

Figures 7.9, 7.10, and 7.11 show examples for single cells and bloc batteries with lead and lead-dioxide electrodes in figure 7.12 a nickel/cadmium cell with pocket plates is shown housed in a steel container.

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