Nickel cadmium, secondary charging

The nickel-cadmium secondary battery contains NiOOH/nickel hydroxide as a positive active material, cadmium/cadmium hydroxide as a negative active material, and an aqueous solution containing potassium hydroxide as the main component as an electrolyte. Generally the charge-and-discharge reaction is shown in the following formulas 1, 2 and 3. 

The vented-type battery needs to perform water addition in which water consumed by electrolysis is periodically added. However, in recent years, the vented-type nickel-cadmium secondary battery which has reduced the water addition frequency is produced commercially for trains and the like. The battery controls the electrolysis of the water under float charging by using the pasted-type cadmium electrode which has a high hydrogen overpotential characteristic for the negative electrode. 

A nickel-cadmium secondary battery with the type of the gas recombination by catalyst in which oxygen and hydrogen gas generated in the end of charging are made to react and return to water by providing a catalyst to the vent valve is used partly. 

Nickel-cadmium cells have a very low ac resistance of 1 mil. The charge state of the cells is of secondary importance. Nickel-cadmium cells must have sufficient current capacity and have current stability. They can be used directly as a dc decoupling device (Fig. 14-6) [6]. 

Secondary batteries can be electrically charged, and these batteries can offer savings in costs and resources. Recently, lithium-ion and nickel-metal hydride batteries have been developed, and are used with the other secondary batteries, such as nickel-cadmium, lead-acid, and coin-type lithium secondary batteries. 

RAM cells are manufactured and shipped charged and have an initial capacity of about 1.8 Ah for AA-sized cells discharged at 50 mA (in comparison with, say, 2 Ah for an equivalent primary cell). This capacity falls to 1 Ah after storage for 3 years at room temperature. At higher drains, the initial capacity drops to about 0.6 Ah at 400 mA (Fig. 6.14). Cells are designed to operate within a temperature range of 0-65°C. The higher internal resistance of RAM cells limits their maximum continuous output current and also their peak output currents in comparison both with primary cells and with nickel-cadmium and nickel-metal hydride secondary cells. A new cell will have an internal resistance of approximately 0.1 2, but this will rise to 0.25 2 with use. 

It must be emphasized that the most appropriate charging regime is very dependent on the cell system under consideration. Some are tolerant to a considerable amount of overcharging (e.g. nickel-cadmium batteries), while for others, such as zinc-silver oxide and most lithium secondary cells, overcharging can result in permanent damage to the cell. Sealed battery systems require special care float charging should not be used and trickle charge rates should be strictly limited to the manufacturer s recommended values, since otherwise excessive cell temperatures or thermal runaway can result. 

The nickel-based systems have traditionally included the following systems -nickel-iron (Ni/Fe), nickel-cadmium (NiCd), nickel metal hydrides (NiMH), nickel hydrogen (Ni/H2), and nickel-zinc (Ni/Zn). Of these, the metal hydride chemistry has been the most successful in the secondary battery market. AU nickel systems are based on the use of a nickel oxide active material (undergoing one valence change from charge to discharge or vice-versa). The electrodes can be pocket type, sintered type, fibrous type, foam type, pasted type, or plastic roll-bonded type. All systems use an alkaline electrolyte, KOH. 

During charging, the secondary cell receives the same amount of electric energy as that previously released, and this is stored in the form of chemical energy (see Figure 1.11 for nickel-cadmium system). Terminal voltage, charging time, number... 

Nickel-cadmium batteries are secondary systems while lithium systems are usually primary devices. This means that, when nickel-cadmium batteries are used, a more complicated circuit is required. This translates to higher part, labour and board costs. In addition, limited nickel-cadmium battery capacity between charges can affect the duration of continuous data retention time. With a lithium cell, the total capacity may be used in one longer, continuous standby cycle. 

Eveready sealed secondary nickel-cadmium cells and batteries are now widely used as a rechargeable power source in many different types of portable or cordless ele trical appliance. Charging at the safe recommended C/10 ratd has proved satisfactory for recharging the cells or batteries used in many of these appliances, such as toothbrushes, shavers, etc., where relatively long rest periods between uses are possible. However, there is now a demand for the use of sealed nickel-cadmium cells and batteries in other applianees, such as chain saws, electronic flashes, portable drills and professional hair elippers, where the rest periods between uses of the applianees are mueh shorter eonsequently shorter reeharging times, from about 3h to about 1 h, that is, C/3 to C/1 rates, are required. 

Unlike the cells above, which are all primary cells, this is a secondary (i.e. rechargeable) cell, and the two poles are composed in the uncharged condition of nickel and cadmium hydroxides respectively. These are each supported on microporous nickel, made by a sintering process, and separated by an absorbent impregnated with electrolyte. The charging reactions are ... 

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