Zinc/mercuric oxide batteries voltage

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. 

The alkaline zinc/mercuric oxide battery is noted for its high capacity per unit volume, constant voltage output, and good storage eharacteristics. The system has been known for over a century, but it was not until World War II that a practical battery was developed by Samuel Ruben in response to a requirement for a battery with a high capacity-to-volume ratio which would withstand storage under tropical conditions. - ... 

FIGURE 11.7 No-load voltage vs. temperature, zinc/mercuric oxide battery. 

Discharge profiles for the DAB and DA675-size zinc/air button batteries are presented in Fig. 13.6. As the air cathode in the cell is not chemically altered during discharge, the voltage remains quite stable. Data for the zinc/mercuric oxide and zinc/silver oxide batteries are provided for comparison. On continuous discharge at the loads shown, the zinc/air battery will deliver twice the service of the other batteries of the same size. The DAB battery, which has less than half the volume of the other batteries, outperforms the larger metal oxide batteries. 

The small mercury and lithium disposable batteries used for calculators and cameras are variations of the alkaline battery. In the mercury battery, mercuric oxide, HgO, is reduced rather than manganese dioxide. Manufacturers are phasing out these batteries because of the environmental hazard posed by mercury, which is poisonous. In the lithium battery, lithium metal is used as the source of electrons rather than zinc. Not only is lithium able to maintain a higher voltage than zinc, it is about 13 times less dense, which allows for a lighter battery. 

The power density of the two batteries described is not enough to cope with miniature circuits, such as in watches and hearing aids. Batteries with very stable voltage and very long life are based on the zinc anode and a mercuric oxide cathode, with an alkaline electrolyte. They are known as mercury cells. The cell reaction is... 

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... 

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