Cadmium/mercuric oxide batteries

Cadmium/Mercuric Oxide Battery. The substitution of cadmium for the zinc anode (the cadmium/mercuric oxide cell) results in a lower-voltage but very stable system, with a shelf life of up to 10 years as well as performance at high and low temperatures. Because of the lower voltage, the watthour capacity of this battery is about 60% of the zinc/mercuric oxide battery capacity. Again, because of the hazardous characteristics of mercury and cadmium, the use of this battery is limited. 

TABLE 11.1 Characteristics of the Zinc/Mercuric Oxide and Cadmium/Mercuric Oxide Batteries... 

An outstanding feature of the cadmium/mercuric oxide battery is its ability to operate over a wide temperature range. The usual operating range is from -55 to +80°C, but with the low gassing rate and thermal stability of the cell, operating temperatures to 180°C have been achieved with special designs. 

The performance of the cadmium/mercuric oxide battery is summarized in Figs. 11.16 and 11.17 on a weight and volume basis, respectively. The data were derived from the performance of typical button batteries. 

FIGURE 11.17 Service life of typical cadmium/mercuric oxide, batteries on a volume basis. 

During the last several years, the market for mercuric oxide batteries has almost completely evaporated, due mainly to environmental problems associated with mercury and cadmium and few are manufactured. They have been removed from the International Electrotechnical Commission (lEC) and the American National Standards Institute (ANSI) standards. In applications, they have been replaced by alkaline-manganese dioxide, zinc/air, silver oxide and lithium batteries. 

The cadmium/mercuric oxide button battery uses a similar configuration. 

FIGURE 11.14 Discharge curves—cadmium/mercuric oxide button battery (500-mAh size). 

Batteries. Many batteries intended for household use contain mercury or mercury compounds. In the form of red mercuric oxide [21908-53-2] mercury is the cathode material in the mercury—cadmium, mercury—indium—bismuth, and mercury—zinc batteries. In all other mercury batteries, the mercury is amalgamated with the zinc [7440-66-6] anode to deter corrosion and inhibit hydrogen build-up that can cause cell mpture and fire. Discarded batteries represent a primary source of mercury for release into the environment. This industry has been under intense pressure to reduce the amounts of mercury in batteries. Although battery sales have increased greatly, the battery industry has aimounced that reduction in mercury content of batteries has been made and further reductions are expected (3). In fact, by 1992, the battery industry had lowered the mercury content of batteries to 0.025 wt % (3). Use of mercury in film pack batteries for instant cameras was reportedly discontinued in 1988 (3). 

There are two major types of household batteries (a) Primary batteries are those that cannot be reused. They include alkaline/manganese, carbon-zinc, mercuric oxide, zinc-air, silver oxide, and other types of button batteries, (b) Secondary batteries are those that can be reused secondary batteries (rechargeable) include lead-acid, nickel-cadmium, and potentially nickel-hydrogen. 

Although several studies carried out in Europe, Japan and the USA concluded that mercury from batteries in waste does not pose a threat to the environment irrespective of the means of disposal, legislation was introduced to control the dispersal of mercury, cadmium and lead from waste batteries into the environment by separately collecting waste mercuric oxide, nickel cadmium and lead-acid batteries. 

Accurate sorting relies on the identification of a number of different properties of a battery. These include the physical size and shape, the weight, the electromagnet properties and any surface identifiers such as colour or unique markings. These properties can be analysed in a number of different combinations in order to sort batteries into nickel cadmium, nickel metal hydride, lithium, lead acid, mercuric oxide, alkaline and zinc carbon batteries. Due to an voluntary marking initiative introduced by the european battery industry, it is now also possible to separate the alkaline and zinc carbon cells further into mercury free and mercury containing streams. 

Over the years, several different battery technologies have been tried. Including mercury-zinc, rechargeable silver-modified-mercuric-oxide-zinc, rechargeable nickel-cadmium, radioactive plutonium or promethium, and lithium with a variety of different cathodes. Lithium-cupric-sulfide and... 

Other cells, based on zinc anodes or on mercuric oxide cathodes are known. Among them are the silver-zinc battery, zinc-copper oxide battery, mercury-cadmium battery etc. 

Mercuric oxide-itidium-bismuth and mercury-cadmium (primary) batteries supplied by Crompton-Parkinson... 

Figure55.6 Mallory No. 304116 12.6V mercuric oxide-cadmium battery two-stage discharge curve. Current drain at 11.5V (Courtesy oi Maliory)...

Crompton-Parkinson supply mereurie oxide-indium-bismuth and mercuric oxidc-cadmium batteries. These arc alkaline systems recommended for applications in which high reliability in particularly onerous longterm storage and use eonditions is a prime requirement. 

---