Zinc-carbon batteries shelf life

Primary batteries have existed for over 100 years, but up to 1940, the zinc-carbon battery was the only one in wide use. During World War II and the postwar period, significant advances were made, not only with the zinc-carbon system, but with new and superior types of batteries. Capacity was improved from less than 50 Wh/kg with the early zinc-carbon batteries to more than 400 Wh/kg now obtained with lithium batteries. The shelf life of batteries at the time of World War n was limited to about 1 year when stored at moderate temperatures the shelf life of present-day conventional batteries is from 2 to 5 years. The shelf life of the newer lithium batteries is as high as 10 years, with a capability of storage at temperatures as high as 70°C. Low-temperature operation has been extended from 0 to -40C, and the power density has been improved manyfold. Special low-drain batteries using a solid electrolyte have shelf lives in excess of 20 years. 

Zinc-Carbon Battery. The Leclanche or zinc-carbon dry cell battery has existed for over 100 years and had been the most widely used of all the dry cell batteries because of its low cost, relatively good performance, and ready availability. Cells and batteries of many sizes and characteristics have been manufactured to meet the requirements of a wide variety of applications. Significant improvements in capacity and shelf life were made with this battery system in the period between 1945 and 1965 through the use of new materials (such as beneficiated manganese dioxide and zinc chloride electrolyte) and cell designs (such as the paper-lined cell). The low cost of the Leclanchd battery is a major attraction, but it has lost considerable market share, except in the developing countries, because of the newer primary batteries with superior performance characteristics. 

The shelf life of the magnesium/manganese dioxide primary battery at various storage temperatures is compared with the shelf life of the zinc-carbon battery in Fig. 9.11. The magnesium battery is noted for its excellent shelf life. The battery can be stored for periods of 5 years or longer at 20°C with a total capacity loss of 10 to 20% and at temperatures as... 

The shelf life of this battery is rather poor, as shown in Fig. 9.8, because of the slow loss of water and because of side reactions due to impurities in the Mn02 ore commonly used. When specially purified Mn02 is used, the performance of the battery is greatly improved. The zinc-carbon dry cell is considered the workhorse of the battery industry It provides power at a very low cost. 

Conventional Systems. Reserve batteries employing the conventional electrochemical systems, such as the Leclanch6 zinc-carbon system, date back to the 1930-1940 period. This stmcture, in which the electrolyte is kept in a separate vial and introduced into the cell at the time of use, was employed as a means of extending the shelf life of these batteries, which was very poor at that time. Later similar stmctures were developed using the zinc-alkaline systems. Because of the subsequent improvement of the shelf life of these primary batteries and the higher cost and lower capacity of the reserve stmcture, batteries of this type never became popular. 

The chemical efficiency of a carbon-zinc battery improves as current density deereases. This reveals an important application principle consistent with physical limitations, use as large a battery as possible. Over a certain range of current density, serviee life may be tripled by halving the current drain. This is equivalent to using a larger battery for a given application and so reducing current density within the cells. This is true to a certain point beyond which shelf deterioration becomes an important factor. 

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