Pocket plates, nickel systems

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)... 

The basic electrochemistry is the same for the vented pocket plate, sintered plate, fiber and plastic-bonded plate types as well as for other variations of the nickel-cadmium system. The reactions of charge and discharge can be illustrated by the following simplified equation ... 

The electrochemically active material of the nickel electrode is nickel hydroxide. This material is an amorphous colloid and is only semiconductive at best. It must be supported and contained by a structural component which provides mechanical support, conductivity and current collection for the electrode. Standard types of nickel electrodes can be used in the nickel-zinc system. They can be classified by the type of electrode substrate used and by the method of preparation. These electrodes consist of two basic types, sintered and nonsin-tered. Each type has different advantages and disadvantages and may be selected based on the application. Other types of nickel electrodes, such as pocket plate, are generally not in common use. 

Both the positive and negative tubular and pocket current collectors are made of perforated nickel-plated steel. They are very robust and are virtually indestructible. The low energy density, poor charge retention, and poor low temperature performance, along with high cost of manufacture, have led to a decUne in use of the nickel-iron battery system. The negative electrode, or anode, is iron and the positive... 

In 1932, Shlecht and Ackermann invented the sintered plate. In those days, conventional plates involved a system in which the active materials were packed into a metal container called a pocket or tube. However, with the sintered-plate method, the active materials are placed inside a porous electrode formed of sintered nickel powder. In 1947, Neumann achieved a completely sealed stracture. This idea of protection against overcharge and overdischarge by proper capacity balance is illustrated in Figure 2.5. 

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