Nickel-manganese dioxide cells

Lithium-magnesium alloys, 15 135 Lithium manganate(V), 15 592 Lithium-manganese dioxide cells, 3 461 characteristics, 3 462t Lithium metaborate, 15 137 Lithium metaborate octahydrate, 4 277 Lithium metal, 15 132 uses for, 15 134 Lithium metal films, 15 128 Lithium methoxide, 15 148 Lithium nickelate, 15 142 Lithium niobate, 15 141 17 153... 

The manufacture of secondary batteries based on aqueous electrolytes forms a major part of the world electrochemical industry. Of this sector, the lead-acid system (and in particular SLI power sources), as described in the last chapter, is by far the most important component, but secondary alkaline cells form a significant and distinct commercial market. They are more expensive, but are particularly suited for consumer products which have relatively low capacity requirements. They are also used where good low temperature characteristics, robustness and low maintenance are important, such as in aircraft applications. Until recently the secondary alkaline industry has been dominated by the cadmium-nickel oxide ( nickel-cadmium ) cell, but two new systems are making major inroads, and may eventually displace the cadmium-nickel oxide cell - at least in the sealed cell market. These are the so-called nickel-metal hydride cell and the rechargeable zinc-manganese dioxide cell. There are also a group of important but more specialized alkaline cell systems which are in use or are under further development for traction, submarine and other applications. 

The development of new products with less or without dangerous substances must be a future goal of priority to avoid hazards to the environment. Good examples are lithium primary and secondary cells and the mercury-free rechargeable alkaline manganese dioxide cell, which is produced at a pilot plant in Canada [57]. But also the nickel-metalhydride cell will be a favourite to supplement and partly substitute nickel-cadmium cells. 

Comparison of the Daniell element, the nickel/cadmium accumulator, and, the lithium/manganese dioxide primary cell, as examples, shows the influence of the electrode materials on different cell parameters (Table 1). 

Cadmium, along with nickel, forms a nickel-cadmium alloy used to manufacture nicad batteries that are shaped the same as regular small dry-cell batteries. However, a major difference is that the nicads can be recharged numerous times whereas the common dry cells cannot. A minor difference between the two types of cells is that nicads produce 1.4 volts, and regular carbon-zinc-manganese dioxide dry-cell batteries produce 1.5 volts. 

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... 

The actual cell voltage is about 1.5 V, it does not depend on the actual pH-value of the electrolyte solution as obvious from the absence of protons and hydroxide ions in the cell reaction equation. It slightly depends on the source of the used manganese dioxide. Initially naturally occurring manganese dioxide was used. The battery required a quality of less than 0.5% copper, nickel, cobalt, and arsenic to avoid undue corrosion of the zinc electrode. Currently synthetic manganese dioxide is prepared either by chemical (CMD) or electrochemical (EMD) procedures. For improved electrical conductivity graphite or acetylene black are added. Upon deep... 

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. 

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. 

The only power sources feasible for all these portables are electrochemical batteries. Disposable batteries were the classical power source for flashlights, and still hold a very strong position (salt Leclanche later, alkaline dry cells of zinc-manganese dioxide type). Rechargeable batteries became ever more important first, nickel-cadmium, and more recently, nickel-hydride and lithium ion batteries. For convenient handling, a power source is usually placed somewhere inside the device, so it should respect certain limitations as to weight and volume. As a rule of thumb, a power source should not exceed 30-40% by mass and volume of the device powered by it. A similar upper limit 30-40% applies to the cost. 

Miniature Cell. The container, seal, and finish materials for the miniature alkaline-manganese dioxide button cell are essentially the same as those for other miniature cells. The can (container and cathode collector) is made of mild steel plated on both sides with nickel. The seat is a thin plastic gasket. The anode cup makes up the rest of the exterior of the cell. The outer surfaces of the can and anode cup are highly finished, with manufacturer identification and cell number inscribed on the can. No additional finish is needed. 

The lead-acid battery system is by far the least costly of the secondary batteries, particularly the SLI type. The lead-acid traction and stationary batteries, having more expensive constmctional features and not as broad a production base, are several times more costly, but are still less expensive than the other secondary batteries. The nickel-cadmium and the rechargeable zinc/manganese dioxide batteries are next lowest in cost, followed by the nickel/metal hydride battery. The cost is very dependent on the cell size or capacity, the smaller button cells being considerably more expensive than the larger cylindrical and prismatic cells. The nickel-iron battery is more expensive and, for this reason among others, lost out to the less expensive battery system. 

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