Portable Sealed Nickel-Cadmium Batteries

In portable applications were batteries are exposed to temperature extremes or rough handling, nickel-cadmium batteries are used for signal lamps, hand lamps, search lights, and portable instmments. Vented spillproof batteries are used in large devices, whereas sealed nickel-cadmium batteries dominate the smaller ones (see Chap. 27). 

For small-size portable rechargeable batteries, the collection of spent nickel cadmium batteries started in 1985 and has been pursued in combination with the collection of nickel metalhydride batteries, lithium ion batteries and small-size sealed lead-acid batteries. The collection rate of nickel cadmium batteries was over 40% in 2000. 

The development of nickel/cadmium batteries started in the beginning of the twentieth century in parallel to that of the nickel/iron battery. The latter played an important role mainly as a sturdy traction battery that reached many charge/ discharge cycles. But after World War II it gradually lost its market, mainly because of the high hydrogen evolution rate and comparatively low power efficiency. The nickel/cadmium battery, however, still has a strong market position, mainly in its sealed version as a portable power source, but also as a flooded battery in traction and stationary applications. 

Hydrogen evolution can also be prevented, and thus the unwanted secondary reactions hydrogen evolution and grid corrosion that disturb the internal oxygen cycle in lead-acid batteries, as shown in Fig. 1.25, are not present in nickel/cadmium batteries, which therefore can be hermetically sealed so that neither vapor or gas escapes from the battery. This is the reason for the market success of these batteries in the field of portable applications. 

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. 

Nickel-cadmium sealed cells are now a commercially important consumer product. They find use, both as button and cylindrical cells, in portable cordless appliances such as power tools, electric razors and photoflash apparatus, and increasingly in hybrid mains/battery equipment such as portable tape recorders, radios and television receivers. Many of these cells are readily interchangeable with primary batteries. In recent years, advances in design have increased recharge rates cylindrical cells with sintered electrodes can now be fast charged from full discharge at up to the C/l rate of 80% of capacity. 

On the other hand, Sanyo Electric Co., Ltd. started mass production of a consumer sealed type nickel-cadmium secondary battery. Then, other companies produced a consumer sealed-type nickel-cadmium secondary battery commercially one after another. Then, the batteries have been used as the main power supply of portable electronic devices such as cordless power tools and toys, video cameras, and notebook PCs in 1980s, and the production amount has enlarged drastically. 

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