Alkaline primaries, zinc electrodes

It is so universally applied that it may be found in combination with metal oxide cathodes (e.g., HgO, AgO, NiOOH, Mn02), with catalytically active oxygen electrodes, and with inert cathodes using aqueous halide or ferricyanide solutions as active materials ("zinc-flow" or "redox" batteries). The cell (battery) sizes vary from small button cells for hearing aids or watches up to kilowatt-hour modules for electric vehicles (electrotraction). Primary and storage batteries exist in all categories except that of flow-batteries, where only storage types are found. Acidic, neutral, and alkaline electrolytes are used as well. The (simplified) half-cell reaction for the zinc electrode is the same in all electrolytes ... 

The major design changes made to primary alkaline cells were the use of improved cathode and anode formulations, the limitation of the anode capacity to approximately 1/3 of the cathode capacity to prevent overdischarge of the cathode, the application of improved separators and the integration of means to enable moderate cell abuse. Cell components (cans and closures) and raw materials (EMD, graphite, zinc) used are identical to the ones used in primary alkaline cells. The electrode capacity balance accounts for the reduced capacity of RAM cells when compared to primary alkaline cells of similar size. 

The zinc electrode in the Zn-air cell has the same basic composition as the zinc powder gel anode, used in the assembly of the alkaline primary cell, and contains less than 0.25 mg/cell mercury as permitted by law. Organic corrosion... 

The separator must serve this purpose in a dynamic environment. Electrodes can change shape and/or volume as a function of age and cycle number electrolytes can age triggering precipitation. The separator must be considered and matched to its system so that it can provide the aforementioned functionality for the design life of the system. Figure 2 indicates the workhorse design of perhaps the most ubiquitous battery and separator material, the zinc-alkaline primary system. 

The design of a AA-size alkaline manganese dioxide cell is shown in Fig. 1 (Sec. 3.1). Primary and secondary alkaline batteries are constructed in the same way and can be manufactured on essentially the same machinery. The separator material, electrode formulation, and the Mn02 Zn balance are different. Rechargeable cells are zinc-limited to prevent a discharge beyond the first electron-equivalent of the MnOz reduction. The electrolyte is 7-9 mol L KOH. The electrode reactions are ... 

Thus, there are two possible modes of utilizing zinc anodes in alkaline solutions. In the first and older mode, only tfie primary process is used, with monolithic zinc anodes and a large volume of electrolyte. In the second mode, the secondary process is employed, with powdered zinc anodes at which the true current densities are much lower than at smooth electrodes. 

Continuous research in primary alkaline manganese batteries ended up in the development of rechargeable alkaline manganese (RAM) cells. The design of these cells dated to 1975 [1], These batteries are basically an extension of the primary alkaline batteries. They also use zinc for the negative electrode, manganese dioxide for the positive electrode, and an aqueous solution of potassium hydroxide for the electrolyte. 

There are many methods of fabricating the electrodes for these cell systems. The earliest commercially successful developments used nickel hydroxide [12054-48-7], Ni(OH)2, positive electrodes. These electrodes are commonly called nickel electrodes, disregarding the actual chemical composition. Alkaline cells using the copper oxide—zinc couple preceeded nickel batteries but the CuO system never functioned well as a secondary battery. It was, however, commercially available for many years as a primary battery (see Batteries-PRIMARY cells). 

The Zn negative electrode material, or anode, and electrolyte solution are similar to other primary alkaline battery types, like zinc-air and zinc-silver oxide (Zn/ Ag20). Zinc powder is mixed with a gelling agent like polyacrylic acid and a KOH-Zn0-H20 electrolyte. 

Alkaline-manganese cells have a lower internal resistance and give a better performance than the ordinary dry cell but are more expensive. The electrolyte is a potassium hydroxide solution. The primary electrode reactions are as before, but the zinc ions react with the hydroxide ions, resulting in precipitation of zinc hydroxide and oxide, so that the over-all cell reaction is... 

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