Zinc-containing manganese dioxide batterie

A lead-acid storage battery is only one type of battery, however. Different batteries use different metals and electrolytes to make them work. For example, alkaline batteries (the ones found in flashlights, toys, and portable electronic devices) contain powdered zinc and manganese dioxide as their electrodes. They use an electrolyte made of an alkaline solution of potassium hydroxide. Most alkaline batteries have a finite amount of chemicals in them. Once the chemicals react with one another, they are used up, and the battery goes dead (is discharged) and cannot be recharged. 

Most of the commercial battery systems, e.g. zinc-carbon, manganese dioxide-zinc, nickel-cadmium, lead-acid and mercury button cells contain toxic substances. Strong efforts have been made to recycle these batteries, to lower the concentration of their toxic substances or to replace them with alternative systems. Nevertheless, battery production processes as well as disposal or recycling activities of spent batteries are responsible for the infiltration of a few toxic substances in our environment. The following chapters describe the toxicology of mercury, cadmium and lead, which are the most toxic components found in different battery systems. 

Zn(OH)2 is soluble in the alkaline solution as [Zn(OH)3]- until the solution is saturated with K[Zn(OH)3]. In addition Zn(OH)2 can be dehydrated to ZnO. An enhanced power density (when compared with the - Leclanche cell) is accomplished by using particulate zinc (flakes) soaked with the alkaline electrolyte solution. This anode cannot be used as a cell vessel like in the Leclanche cell. Instead it is mounted in the core of the cell surrounded by the separator the manganese dioxide cathode is pressed on the inside of the nickel-plated steel can used as battery container. In order to limit self-discharge by corrosion of zinc in early cells mercury was added, which coated the zinc effectively and suppressed hydrogen evolution because of the extremely low exchange current density... 

Batteries. Processes in batteries and car lead accumulators can now be examined and clearly interpreted. In a Feclanche battery, there is a zinc container, which represents the negative pole. The positive pole is formed by a graphite rod, which is surrounded from a mixture of carbon and manganese dioxide (see Fig. 8.5). 

Types of activated carbon which have electrical conductivity can be used instead of manganese dioxide as a depolarizer in dry-cell batteries.77 Powdered activated carbon is treated with ammonium chloride and pressed into a porous cylindrical shape that is placed in a zinc container forming the outer electrode. If provision is made for a sufficient. supply of air, the effect of the activated carbon cylinder is similar to that of"manganese dibxide. The potential of the activated carbon batter is 0.1 volt lower than that of the manganese dioxide type, but the voltage is steadier and is practically constant throughout the life of the battery. 

The zinc-air treatment is somewhat simpler because the absence of manganese dioxide means that the acid treatment is not necessary. After the batteries have been opened, they are immersed in sodium hydroxide within a trummel. The fines, containing zinc powder, zinc oxide, carbon and lime are suspended in solution and undergo the same zinc treatment as described above. After washing, the large fraction consisting of polypropylene pieces, steel and carbon are sorted and recycled within specialist industries. 

Alkaline cells use the same zinc-manganese dioxide couple as Leclanche cells. However, the ammonium chloride electrolyte is replaced with a solution of about 30 wt% potassium hydroxide (KOH) to improve ionic conductivity. The ceU reactions are identical to those above, but the battery construction is rather different (Figure 9.7). The negative material is zinc powder, and the anode (negative terminal) is a brass pin. The positive component is a mixture of Mn02 and carbon powder that surrounds the anode. A porous cylindrical barrier separates these components. The positive terminal (cathode) is the container, which is a nickel-plated steel can. 

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