Nickel-cadmium battery additives

The electrochemical equivalent of about 480 Ah kg is one of the lowest for all metallic anodes, and the OCV of 1.35 V for the Nicad is not favorable for many applications. Studies of failure mechanisms [26] revealed that the cadmium electrode is responsible for capacity loss and memory effect of the nickel/cadmium battery. Additionally, it is desirable to restrict the use of cadmium for environmental reasons. The consequence is a continuous retreat of this system from many applications, and battery packs for electric tools may eventually be the only remaining use. 

The composition of EAF dust can vary greatly, depending on scrap composition and furnace additives. EAF dust usually has a zinc content of more than 15%, with a range of 5 to 35%. Other metals present in EAF dust include lead (2-7%), cadmium (generally 0.1-0.2% but can be up to 2.5% where stainless steel cases of nickel-cadmium batteries are melted), chromium (up to 15%), and nickel (up to 4%). 

Subcategory A encompasses the manufacture of all batteries in which cadmium is the reactive anode material. Cadmium anode batteries currently manufactured are based on nickel-cadmium, silver-cadmium, and mercury-cadmium couples (Table 32.1). The manufacture of cadmium anode batteries uses various raw materials, which comprises cadmium or cadmium salts (mainly nitrates and oxides) to produce cell cathodes nickel powder and either nickel or nickel-plated steel screen to make the electrode support structures nylon and polypropylene, for use in manufacturing the cell separators and either sodium or potassium hydroxide, for use as process chemicals and as the cell electrolyte. Cobalt salts may be added to some electrodes. Batteries of this subcategory are predominantly rechargeable and find application in calculators, cell phones, laptops, and other portable electronic devices, in addition to a variety of industrial applications.1-4 A typical example is the nickel-cadmium battery described below. 

Cadmium, as cadmium oxide, is obtained mainly as a by-product during the processing of zinc-bearing ores and also from the refining of lead and copper from sulfide ores (USPHS 1993). In 1989, the United States produced 1.4 million kg of cadmium (usually 0.6 to 1.8 million kg) and imported an additional 2.7 million kg (usually 1.8 to 3.2 million kg). Cadmium is used mainly for the production of nickel-cadmium batteries (35%), in metal plating (30%), and for the manufacture of pigments (15%), plastics and synthetics (10%), and alloys and miscellaneous uses (10%) (USPHS 1993). 

To protect humans and other mammals, proposed air-quality criteria range from 0.01 to less than 1.0 mg/m3 for metallic nickel and slightly soluble nickel compounds, 0.015-0.5 mg/m3 for water soluble nickel compounds, and 0.005 to 0.7 mg/m3 for nickel carbonyl (Table 6.10). Inhalation of nickel subsulfide concentrations (0.11 to 1.8 mg Ni/m3) near the current threshold limit value of 1 mg Ni/m3 can produce detrimental changes in the respiratory tract of rats after only a few days of exposure (Benson et al. 1995). Additional animal studies are recommended to identify minimally effective inhalation exposure levels for the various nickel compounds (USPHS 1993). Continued monitoring of nickel refining, nickel-cadmium battery manufacture, and nickel powder metallurgy installations is recommended because ambient air levels of bioavailable nickel at these... 

Flooded battery — A battery (or a cell) containing an excess of electrolytic solution (in contrast to starved electrolyte batteries). Usually relevant to rechargeable -> lead-acid and -> nickel-cadmium batteries. Flooded battery design is typically applicable for heavy duty batteries, equipped with a vent valve that releases pressure buildup due to gas evolution. The excess electrolyte affects more sturdy batteries to become less susceptible to damage due to overcharge. In addition, the thermal conductivity of the electrolyte affords more efficient heat dissipation and thus higher -> power densities. 

Nickel. Although not an alloying element, nickel enters the lead stream through the addition of nickel-cadmium battery scrap (unintentional and/or intentional) or stainless-steel parts to the furnace. It is removed from lead by the addition of caustic soda at the solidus point of the alloy. 

Even when considered on a long term basis, there is considerable doubt that the presence of land filled battery metals such as lead, zinc, and cadmium would have the catastrophic environmental effects which some have predicted. Studies on 2000-year old Roman artifacts in the United Kingdom (Thornton 1995) have shown that zinc, lead and cadmium diffuse only very short distances in soils, depending on soil type, soil pH and other site-specific factors, even after burial for periods up to 1900 years. Another study in Japan (Oda 1990) examined nickel-cadmium batteries buried in Japanese soils to detect any diffusion of nickel or cadmium from the battery. None has been detected after almost 20 years exposure. Further, it is unclear given the chemical complexation behavior of the metallie ions of many battery metals exactly how they would behave even if metallic ions were released. Some studies have suggested, for example, that both lead and cadmium exhibit a marked tendency to complex in sediments and be unavailable for plant or animal uptake. In addition, plant and animal uptake of metals such as zinc, lead and cadmium has been found to depend very much on the presence of other elements such as iron and on dissolved organic matter (Cook and Morrow 1995). Until these behavior are better understood, it is unjustified to equate the mere presence of a hazardous material in a battery with the true risk associated with that battery. Unfortunately, this is exactly the method which has been too often adopted in comparison of battery systems, so that the true risks remain largely obscured. 

With hydrometallurgical processes, the presence of NiCd or NiMH batteries requires an additional stage in order to isolate the cadmimn, in nickel-cadmium batteries, and the nickel found in certain batteries at a content of less than 0.1% and in the form of nickel steel or an electrolytic nickel coating. 

In contrast to the sector of conventional trucks, practically all systems of batteries, which have proved successful in practice, are used in driverless industrial trucks. In addition to the lead-acid batteries (LAB) common in the sector of conventional industrial trucks nickel/cadmium batteries (NCB) have taken over quite a considerable slot in the market in the DIT sector, on account of their particular properties. 

The lEC has been considering a new nomenclature system, possibly covering both primary and rechargeable batteries but none have yet been published. Table 4.4a lists the letter codes that are being considered by lEC and those adopted by ANSI for secondary or rechargeable batteries. The lEC nomenclature system for nickel-cadmium batteries is shown in Table. 4.4b. In this system, the first letter designates the electrochemical system, a second letter the shape, the first number of the diameter, and a second number the height. In addition. 

Most of the operating characteristics of the sealed nickel-metal hydride battery on discharge are similar to those of the nickel-cadmium battery. The sealed nickel-metal hydride battery, however, does not have the very high rate capability of the nickel-cadmium battery. In addition, the behavior of the two systems on charge, particularly on fast charge, is different. The nickel-metal hydride battery is less tolerant of overcharge and requires control of the cutoff of the charge, which may not always be required for nickel-cadmium batteries. 

Examples of EV NiMH battery packs for the General Motors EVl and S-10 pickup truck are shown in Fig. 30.1. In addition, nickel metal-hybride batteries are being used in industrial applications, replacing nickel-cadmium batteries and are being considered as a replacement for lead-acid batteries in SLI applications. 

Additionally, in 1901, the Swedish engineer Waldemar Jungner and Thomas Edison invented the rechargeable nickel-cadmium battery, whose redox reaction during the charge and discharge processes is shown in Equation 1.2, and its open-circuit voltage is about 1.35 V. 

The nickel-cadmium battery is mechanically ragged and long lived, hi addition it has excellent low-temperature characteristics and can be hermetically sealed. Cost, however, is higher than for either the lead-acid or the nickel—zinc battery and, by comparison, its capacity on light drain in terms of watt hours per kilogram is also poorer than for nickel-zinc. 

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