Ni-Cd Batteries

Primary cadmium prices rose sharply ia 1987—1988, from 3.60 to 15.50/kg ia 1—5 metric ton lots (13), largely as a result of speculative stockpiling and strong demand driven by rapid growth in the Ni—Cd storage battery market. Prices decreased just as sharply in 1990—1991 however, reaching 3.15/kg in late 1990, as a result of erosion of consumer stockpiles, regulatory pressures, and a slow-down in the Ni—Cd battery market (14,15). 

Figure 5. Electrode capacity balance of a sealed Ni-Cd battery.

Figure 8. Charge characteristics of an Ni-Cd battery at a constant current (cell type 1200SC temperature 20 °C).

Nickel-cadmium batteries are rechargeable because the nickel and cadmium hydroxides products adhere tightly to the electrodes. More than 1.5 billion Ni-Cd batteries are produced every year. These batteries are not without drawbacks, however. Cadmium is a toxic heavy metal that adds weight to the battery. Moreover, even rechargeable batteries degrade eventually and must be recycled or disposed of in a benign way. 

Nowadays, such hydride electrodes are used widely to make alkaline storage batteries which in their design are similar to Ni-Cd batteries but exhibit a considerably higher capacity than these. These two types of storage battery are interchangeable, since the potential of the hydride electrode is similar to that of the cadmium electrode. The metal alloys used to prepare the hydride electrodes are multicomponent alloys, usually with a high content of rare-earth elements. These cadmium-free batteries are regarded as environmentally preferable. 

Fishbein, B., Extended Product Responsibility A New Principle for Product-Oriented Pollution Prevention, Industry Program to Collect and Recycle Nickel-Cadmium (Ni-Cd) Batteries, U.S. Environmental Protection Agency, EPA530-R-97-009, Washington, DC, pp. 6-1-6-32, 1997. 

There are two main uses for cadmium in batteries (particularly Ni-Cd batteries), which account for almost three quarters of the consumption, and in pigments and plastics stabilizers. 

Nogueira, C. A. Delmas, F. New flowsheet for the recovery of cadmium, cobalt and nickel from spent Ni-Cd batteries by solvent extraction. Hydrometallurgy 1999, 52, 267-287. 

Sze, Y. K. P. Lam, J. K. S. A study of a solvent extraction method for the treatment of spent electrolyte solutions generated in nickel-cadmium (Ni-Cd) battery manufacturing. Environ. Technol. 1999, 20, 943-951. 

It can be seen that an energy of ca. 150 kJ/kg, comparable to that accumulated in Pb02-Pb or Ni-Cd batteries, can be obtained at voltages of 4V. Somewhat lower energy (100 kJ/kg) is accumulated at a voltage of 3V. Consequently, the searched system carbon/electrolyte should be characterised by (i) specific capacity. > 160 F per gram of activated carbon and (ii) electrochemical stability window at the level of ca. >3V. 

The most important metalliferous liquid effluents where solvent extraction could be applied are from the various metal finishing operations plating, pickling, etching, and the wash waters arising from the cleaning of work pieces. In the case of solids, in addition to scrap metal and alloy wastes from manufacturing operations, a number of other products use valuable and toxic metals and offer potential applications, e.g., spent automobile catalysts, Ni/Cd batteries, etc. 

In sealed cells, which are the most important kind of Ni-Cd batteries, the gas (H2 and O2) evolution accompanying discharge should be minimized. This can be achieved by incorporation of antipolar mass - cadmium hydroxide in the positive electrode. In this case overdischarge results in reduction of Cd(OH)2 to Cd, instead of hydrogen evolution [348]. On the other hand, oxygen evolved on the positive electrode during overcharging can react with cadmium [348] ... 

Another type of rechargeable battery is the nickel-cadmium, Ni-Cd, battery, cadmium acts as an anode, and nickel (IV) oxide is reduced to nickel (II) hydroxide, Ni(0H)2, at the cathode. As in the lead storage battery, the nickel-cadmium type can be recharged indefinitely. 

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