Cadmium-based cells

Cadmium (Cd) anode cells are at present manufactured based on nickel-cadmium, silver-cadmium, and mercury-cadmium couples. Thus wastewater streams from cadmium-based battery industries carry toxic metals cadmium, nickel, silver, and mercury, of which Cd is regarded the most hazardous. It is estimated that globally, manufacturing activities add about 3-10 times more Cd to the atmosphere than from natural resources such as forest fire and volcanic emissions. As a matter of fact, some studies have shown that NiCd batteries contribute almost 80% of cadmium to the environment,4,23 while the atmosphere is contaminated when cadmium is smelted and released as vapor into the atmosphere4 Consequently, terrestrial, aquatic, and atmospheric environments become contaminated with cadmium and remain reservoirs for human cadmium poisoning. 

All the zinc-based cells, except for the alkahne manganese cell under certain conditions, are primary cells. Secondary (rechargeable) cells are generally based on cadmium rather than zinc, especially in the form of nickel-cadmium cells. 

Si-based cells. The Weston standard cell (cell 22.5) uses a Cd/Hg amalgam cathode, but use of this cell is declining. Cadmium is toxic and environmental legislation in the European Union and US in particular has led to a reduction in its use. Cadmium used in NiCd batteries can be recycled, but its use in other areas is expected to decrease. 

The separator system and the solubility of the active materials play critical roles in determining the wet and cycle lives of the silver-based cells. The separator must have a low electrolytic resistance for discharges at high rates, yet it must have high resistance to chemical oxidation hy the silver species as well as low permeability to colloidal silver, zinc, cadmium, or iron. 

Copper Sulfide—Cadmium Sulfide. This thin-film solar cell was used in early aerospace experiments dating back to 1955. The Cu S band gap is ca 1.2 eV. Various methods of fabricating thin-film solar cells from Cu S/CdS materials exist. The most common method is based on a simple process of serially overcoating a metal substrate, eg, copper (16). The substrate first is coated with zinc which serves as an ohmic contact between the copper and a 30-p.m thick, vapor-deposited layer of polycrystaUine CdS. A layer is then formed on the CdS base by dipping the unit into hot cuprous chloride, followed by heat-treating it in air. A heterojunction then exists between the CdS and Cu S layers. 

Heller A, Chang KC, Miller B (1977) Spectral response and efficiency relations in semiconductor liquid junction solar cells. J Electrochem Soc 124 697-700 Elhs AB, Kaiser SW, Wrighton MS (1976) Optical to electrical energy conversion. Characterization of cadmium sulfide and cadmium selenide based photoelectrochemical cells. J Am Chem Soc 98 6855-6866... 

Elhs AB, Kaiser SW, Bolts JM, Wrighton MS (1977) Study of n-type semiconducting cadmium chalcogenide-based photoelectrochemical cells employing polychalcogenide electrolytes. J Am Chem Soc 99 2839-2848... 

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. 

Hariskos, D. Ruckh, M. Ruehle, U. Walter, T. Schock, H. W. Hedstroem, J. Stolt, L. 1996. A novel cadmium free buffer layer for Cu(In,Ga)Se2 based solar cells. Solar Energy Mater. Solar Cells 41 12 345-353. 

A nicad cell has a cadmium electrode and another electrode that contains nickel(lll) oxyhydroxide, NiO(OH). When the cell is discharging, cadmium is the anode. When the cell is recharging, cadmium is the cathode. The electrolyte is a base, sodium hydroxide or potassium hydroxide. 

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