Zinc Electrodes for Alkaline Primaries

The alkaline version of the Mn02/zinc cell follows a different concept because it turns the construction of the Ledanche cell completely around now the cathode (Mn02 + carbon) forms a hollow cylinder contacting the inner wall of the cell container (steel) along its outer surface. The itmer cavity has to accommodate anode, electrolyte, separator, and current collector. Usually, the separator forms 

Anodic active species and electrolyte are provided as a gel consisting of zinc powder, aqueous KOH solution (7-9 mol L ), gelling agents, and additives. Finally the current collector (a brass nail spot-welded to the metallic part of the cell top) is introduced when the cell top is placed and the can is crimped to give a gas-tight closure. 

The two other alkaline cells of this section (using HgO or an oxygen electrode as cathode) were almost exclusively produced as small button cells. Larger zinc/air batteries gained some attention as candidates for electric vehicle propulsion [124]. 

The discharge reactions now include formation of hydroxo complexes, preferably  

Depending on electrolyte saturation and KOH concentration, subsequent precipitation reactions may follow  

The change from zinc sheet to zinc powder improved the high-current performance of the cell significantly but it increased the corrosion problems (a larger specific surface means a higher corrosion rate). 

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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 ... 

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 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. 

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. 

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. 

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