Nickel-cadmium cells electrolyte

Dry cells (batteries) and fuel cells are the main chemical electricity sources. Diy cells consist of two electrodes, made of different metals, placed into a solid electrolyte. The latter facilitates an oxidation process and a flow of electrons between electrodes, directly converting chemical energy into electricity. Various metal combinations in electrodes determine different characteristics of the dry cells. For example, nickel-cadmium cells have low output but can work for several years. On the other hand, silver-zinc cells are more powerful but with a much shorter life span. Therefore, the use of a particular type of dry cell is determined by the spacecraft mission profile. Usually these are the short missions with low electricity consumption. Diy cells are simple and reliable, since they lack moving parts. Their major drawbacks are... 

Secondary cells are voltaic cells that can be recharged repeatedly. The lead storage battery and nickel-cadmium cell are examples of secondary cells. The lead storage battery consists of six voltaic cells. Its electrodes are lead alloy plates, which take the form of a grill, filled with spongy lead metal. The cathode consists of another group of plates filled with lead (IV) oxide, P6O2. Dilute sulfuric acid is the electrolyte of the cell. When the battery delivers a current, the lead is oxidized to lead ions, which combine with sulfate fS0 7 ions of the electrolyte to cover the lead electrode. 

The manufacture of secondary batteries based on aqueous electrolytes forms a major part of the world electrochemical industry. Of this sector, the lead-acid system (and in particular SLI power sources), as described in the last chapter, is by far the most important component, but secondary alkaline cells form a significant and distinct commercial market. They are more expensive, but are particularly suited for consumer products which have relatively low capacity requirements. They are also used where good low temperature characteristics, robustness and low maintenance are important, such as in aircraft applications. Until recently the secondary alkaline industry has been dominated by the cadmium-nickel oxide ( nickel-cadmium ) cell, but two new systems are making major inroads, and may eventually displace the cadmium-nickel oxide cell - at least in the sealed cell market. These are the so-called nickel-metal hydride cell and the rechargeable zinc-manganese dioxide cell. There are also a group of important but more specialized alkaline cell systems which are in use or are under further development for traction, submarine and other applications. 

As in the nickel-cadmium cell, the electrolyte is concentrated potassium hydroxide. Depending on the metal alloy used, the emf has a value usually in the range 1.32-1.35 V, which turns out to be almost the same as that of the nickcl-cadmium cell. Note that the electrolyte composition is completely invariant during cycling. Unlike the situation with the nickel-cadmium cell, water is not involved in the cell reaction. 

Button, cylindrical and prismatic sealed cells are similar in design to the starved-electrolyte configuration of nickel-cadmium cells. A schematic diagram of a six-cell battery is shown in Fig. 6.11. Because of the slightly... 

The electrolyte is aqueous KOH with a density of approximately 1.22-1.30 g/cm3 at with 1-2% LiOH addition, as for nickel-cadmium cells. 

Ni-Cd cells — The nickel-cadmium cell is a secondary - battery that has a nominal cell potential of 1.20-1.25 V. The negative electrode comprises nickel hydroxide-nickel oxyhydroxide, the positive electrode is cadmium, and the electrolyte solution is based on aqueous potassium hydroxide (KOH, 32% in water). At the anode, the discharge reaction is the oxidation of cadmium metal to cadmium hydroxide with the release of two electrons [i] ... 

Nickel-cadmium cell (nicad battery) A dry cell in which the anode is Cd, the cathode is Ni02, and the electrolyte is basic. 

Lawrence HT, Albert HZ (1996) Electrolyte management considerations in modem nickel/hydrogen and nickel/cadmium cell and battery designs. J Power Sources 63 53-61... 

The nickel—cadmium cell (nicad cell) is a conunou storage battery. It is a voltaic cell consisting of an anode of cadmium and a cathode of hydrated nickel oxide (approximately NiOOH) on nickel the electrolyte is potassium hydroxide. Nicad batteries are used in calculators, portable power tools, shavers, and toothbrushes. The half-cell reactions during discharge are... 

One major disadvantage of the nickel-alkaline battery is the alkaline electrolyte, which picks up CO2 from the atmosphere and must therefore be replaced periodically. However, the advantages of the nickel-cadmium cell over the lead-acid battery are numerous some of these are as follows ... 

Vented sintered-plate nickel-cadmium cells, in the discharged state, consist of flat positive nickel hydroxide and negative cadmium hydroxide plates, separated by materials that act as a gas barrier and electrical separator. The electrolyte, normally a 31% potassium hydroxide solution completely covers the plates and separators for this reason vented cells are referred to as flooded cells. ... 

Calcium-lead alloy batteries, because of the gelled electrolyte, are insensitive lo orientation, as are scaled nickel-cadmium cells. They can therefore be stored, charged or discharged in any position, even upside-down. This characteristic has obvious advantages in cyclic or float applications such... 

Figure 19.16 Overcharge pressure against electrolyte quantity Eagle Richer split negative electrode stack design sealed nickel-cadmium cell. Charge250%, rate C/10, temperature 20°C (Courtesyof Eagle Pichei)...

Potassium hydroxide solutions between 30 and 40% by weight are the usual electrolytes for the cell. Cell constructions, prismatic and flat, are similar to those used for nickel-cadmium cells. 

The nickel-metal hydride couple lends itself to a wound eonstruetion similar to that used by present-day wound niekel-eadmium cells. The basie components consist of the positive and negative eleetrodes insulated by plastic separators similar to those used in nickel-cadmium products. The sandwiched electrodes are wound together and inserted into a metallic can which is sealed after injection of a small amount of potassium hydroxide electrolyte solution. Tne result is a cell which bears a striking resemblance to current sealed nickel-cadmium cells. The nickel-metal hydride chemistry is also applicable to prismatic cell designs which evoke greater interest as product profiles become thinner. 

The reference voltage for the discriminator is matched to the temperature coefficient of the cells that is, —4mV/cell per "C. The Varta TSL system provides a safe and reliable method of fast charging sealed nickel-cadmium cells and batteries. Because of cell tolerances and variations in operating conditions, Varta do not recommend the use of more than ten cells per discriminator. For electrolyte temperatures up to 50°C it is recommended that the charge rate should not be less than the 10 x l o rate, and for electrolyte temperatures not exceeding 35°Cthe charge rate should not be less than 5 x /iq. Provided these... 

Potassium hydroxide A chemical compound, symbol KOH, which, when mixed with pure water in the correct proportions, is the electrolyte solution used in nickel-cadmium cells and other alkaline cell systems. 

In nickel-cadmium cells Cd replaces Fe in these equations. All the materials are insoluble, and the only change in the electrolyte is a slight increase in concentration as water is used in the reaction. 

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