We contacted the manufacturer of lead storage batteries, the AFA enterprise in Česká Lípa. The enterprise is part of the Varta Bosch group and employs a new technology termed Pb-Ca. The business representative of the company, who visited our school, gave us a variety of promotion documentation and prospectuses, but we did not learn much about the chemical side of the manufacture. Thanks to the co-operation with the German partner, the production output incrased considerably and should further increase. In 1992 the factory produced 100 thousand, in 1994 1.5 million storage batteries. The plan for 2000 is 3 million batteries. 70 – 80 % of the production is exported. Lead storage batteries are manufactured also by the AKUMA enterprise in Mladá Boleslav.
The storage battery comprises a set of galvanic cells joined together in series. A spontaneous reaction takes place in the cell during power take-off. Chemical energy is converted into electrical work. Conversely, when energy is supplied from an external source, inverse, non-spontaneous reactions occur at the electrodes.
The most common are still lead storage batteries in which sulphuric acid serves as the electrolyte. The cell, whose internal arrangement is schematically shown in the drawing, can be described as follows:
The overall cell reaction is:
Pb (s) + PbO2 (s) + 4 H+ (aq) + 2 SO42- (aq) ® PbSO4 (s) + 2 H2O (l)
During battery charging, the reactions proceed from right to left (it is a reversible cell).
In a fully charged condition the cell voltage is 1.2 V, and a battery composed of six cells thus provides a voltage of 12.6 V. The density of sulphuric acid at 20 oC is 1.28 g.cm-3, which corresponds to 37.7 % by weight. The solidification point of this solution is –47 oC so that there is practically no danger of the battery freezing up. However, at low temperatures the viscosity rises and the movement of ions consequently slows down, the resistance of the electrolyte increases, the battery cannot deliver sufficient current and behaves as if it were discharged. It is sufficient to take the battery for some time into a warm room in order to restore its function.
The equations show that during the battery discharging the concentration of the acid decreases while during recharging it rises. It is thus not necessary to fill up the acid in the battery, only the water which is lost by evaporation. With modern maintenance-free batteries it is not necessary to fill up any liquid.
Although these reactions are theoretically reversible, storage batteries have a limited service life. The plates are gradually covered with a thin layer of poorly soluble PbSO4 modification - the so-called electrode sulphation. The service life has been prolonged thanks to technological innovations, but worn-out storage batteries still represent a dangerous waste which arises on a mass scale.
Battery recycling in the Czech Republic is carried out by Kovohutě Příbram.. We found that, from September 1997, the enterprise has a new furnace producing metal lead from lead waste, particularly from old storage batteries. The new technology includes special filters which trap dust that contains lead in different forms (Pb, PbO, Pb3O4, PbSO4, PbS) with high efficiency. During 1996, the emissions amounted to 20 tonnes Pb; at present, after a trial operation, the emissions are assumed to reach a maximum of 2.1 tonnes per year.
The history of electromobiles is unexpectedly long. The first electromobiles were constructed as early as 1888. In the initial years of the 20th century, the number of electromobiles in operation in the USA was about 20 thousand, in London more than 10 thousand, and most taxicabs in Berlin and New York were electrically driven. Today, electromobiles are also used in city traffic. They have mostly the lead storage batteries. Their drawback is large weight, and new storage battery systems are therefore sought. An example of these drives is the system
which has been developed by Ford in USA (1966). As compared with lead storage batteries, it has a 5-fold higher capacity per unit weight, a cheap and environmentally clean operation. Among the drawbacks are the necessity of more frequent charging, long charging time, and the need to keep the temperature at 300 - 350 oC in order to keep the resulting sodium polysulphides in a liquid state.
After 2003, 10% of cars sold in California should comply with a zero-emission requirement. In practice, this requirement can be met only by electrically driven cars. General Motors has developed an electromobile which weighs 1350 kg (out of this 535 kg storage batteries) and is very dynamic. The main problem is the small cruising distance - about 145 km outside cities - covered by the car per one charging. For this reason, GM is developing a device, which should shorten the charging time from several hours to 10 - 15 min.
