Mercury-Zinc Batteries

Primary batteries, mercury-zinc, silver-zinc, lithium solid electrolyte types. 

Duracell Deutschland Technical Division, D-5020 Frechen, Hermann-Seger-Strasse 13 Primary batteries, mercury—zinc, silver—zinc, lithium solid electrolyte types. 

Duracell UK Technical Division Duracell House Gatwick Road, Crawley RHIO 2PA Primary batteries, mercury-zinc, silver-zinc, lithium solid electrolyte types, nickel-cadmium, lithium-sulphur dioxide, lithium-manganese dioxide, zinc-air. See also Duracell (US)... 

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). 

Dry-battery mercury anodes are pressed compacts of zinc—mercury amalgam. They were first developed and produced during World War II for walkie-talkie communica tion systems. Practically all hearing aids employ this type of battery in the 1990s. 

Closely related to the alkaline dry cell is the mercury battery, often used in watches, heart pacemakers, and other devices where a battery of small size is required (Figure 18.10). The anode of the mercury battery is zinc, as in the alkaline dry cell, but the cathode is steel in contact with mercury(II) oxide (HgO) in an alkaline medium of KOH and Zn(OH)2. Zinc is oxidized at the anode, and HgO is reduced at the cathode ... 

Mercury and Silver (Button) Batteries Mercury and silver batteries are quite similar. Both use a zinc container as the anode (reducing agent) in a basic medium. The mercury battery employs HgO as the oxidizing agent, the silver uses Ag20, and both use a steel can around the cathode. The solid reactants are compacted with KOH and separated with moist paper. The half-reactions are... 

There is really very little consistency across these environmental impact assessment methods except that the Swedish and Dutch systems rate cadmium the battery metal with the most adverse effects, while the Tellus and Ecoscarcity Methods rate mercury the most adverse battery metal. Zinc, manganese, nickel and even lead have relatively low effects except in the U.S. EPA system, which however is the one system which is most closely tied to actual quantitative assessments of enviromnental and human health toxicological end points. What is very surprising is the relatively low impact values for mercury in the Swedish and Dutch schemes given the general worldwide concern for mercury. 

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... 

The zinc-mercury oxide button cell (Fig. 23.8) uses a pellet of mercury oxide with a little graphite added to it for better conductivity as cathode. The anode of this battery is zinc powder (pressed or amalgamated). The electrolyte, a concentrated ZnO saturated potassium hydroxide solution, is on a cellulose felt. The following shows the simplified processes at the electrodes ... 

There are two construction types of batteries (i) miniature batteries, similar to the mercury-zinc button batteries, which are now produced and used in large quantities for hearing aids and for wrist watches and (ii) comparatively large automatic activated reserve-type batteries, which are activated by a forced injection of the alkaline electrolyte into the electrode compartment and which are mainly employed for aerospace applications. 

Figure 3.2. Typical battery discharge curves. 1— Steep discharge curve typical, for example, for Leclanche cells 2— flat discharge curve typical, for example, for mercury-zinc cells 3—discharge curve with initial dip typical, for example, for thionyl chloride-hthium cells.

Alkaline mercury-zinc batteries were manufactured as sealed cells of low capacity (0.05-15 Ah). They contain mercury oxide HgO and a limited amount of electrolyte (about 1 ml/Ah) absorbed in a porous matrix, so they operate only according to the secondary process of the zinc electrode. Modern mercury-zinc batteries were developed by S. Ruben in the beginning of the 1940s. His button construction was so effective that large-scale production started in the United States as early as World War II and after the war in other countries. A schematics of the button construction is shown in Figure 4.1... 

Figure 4.1. Alkaline mercury-zinc button battery.

Mercury-zinc batteries have a very stable open-circuit voltage (OCV) (1.352 0.002 V). 

Miniaturized button batteries (all three dimensions below 8-10 mm) were used for hearing aids and similar small-sized appliances. For some time hearing aid batteries were based on the mercury-zinc system. Because of the toxicity of mercury compounds, the production and use of mercury-zinc batteries in many countries were held up and they are now replaced with silver-zinc or zinc-air batteries. 

Besides the family of manganese dioxide cells with zinc as negative electrode during the last decades manifold other battery systems have been developed and produced for the market. More capacity and higher load ability were the motivation for research. Here can be named the mercury zinc cell, produced in millions of button cells each year for hearing aids, calculators, watches, cameras, etc. Never was it possible to create one universal cell doing the job for all kinds of applications. Always it has to be noticed that primary cells are specialists, exactly designed for a special application. So in 1980 the smallest button cell of the world was made by Varta with a diameter of 6.8 mm and a thickness of 0.7 mm for wristwatches. 

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. 

Within each Part, chapters are included on all available types of primary batteries, secondary batteries and batteries available in primary and secondary versions. The primary batteries include carbon-zinc, carbon-zinc chloride, mercury-zinc and other mercury types, manganese dioxide-magnesium perchlorate, magnesium organic, lithium types (sulphur dioxide, thionyl chloride, vanadium pentoxide, iodine and numerous other lithium types), thermally activated and seawater batteries. Batteries available in primary and secondary Corms include alkaline manganese, silver-zinc, silver-cadmium, zinc-air and cadmium-air. The secondary batteries discussed include lead-acid, the nickel types (cadmium, iron, zinc, hydrogen), zinc-chlorine, sodium-sulphur and other fast ion types. 

The volumetric ampere hour capacity of mercuric oxide-zinc cells is higher than that of lithium-based systems. However, in many cases using two lithium cells in parallel or one larger lithium cell will give the same ampere hour capacity that can be achieved in an equal or even smaller volume than an equivalent two-cell series mercury-zinc battery of similar voltage. This is illustrated in Table 2.7, which gives a... 

Mercury-zinc primary batteries 8/3 8.2 Mercury-indium-bismuth and mercury-cadmium primpiy batteries 8/3... 

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