Performance zinc-carbon cells

Carbon-zinc cells are distinguished by the composition of the electrolyte. The Leclanche cell has an aqueous ammonium chloride-zinc chloride electrolyte. The higher performance zinc chloride cell mainly has zinc chloride electrolyte and may contain a small amount of ammonium chloride. Cells are available in cylindrical and flat plate constructions, as well as combinations of cells for higher voltage applications. Approximately 30 billion carbon-zinc cells are manufactured annually. 

The zinc chloride cell is a high performance version of the carbon-zinc cell. As its name implies, the zinc chloride cell uses a ZnCl2 electrolyte, along with synthetic or electrolytic Mn02 (EMD). The cell reaction is given in Equation 10.2. 

The advantage of zinc-air cells also presents a big challenge for battery designers. Remaining open to the atmosphere renders zinc-air cells exposed to detrimental environmental conditions, especially humidity. Water in humid air can be absorbed by the basic electrolyte solution diluting it and subsequently flooding the cathode. Arid air may evaporate water from the electrolyte and dry the cathode. Both conditions lead to reduced cell performance and battery life. Carbon dioxide in the air can enter the cell, react with the basic electrolyte solution and precipitate carbonates, also decreasing performance. 

The alkaline zinc-manganese dioxide ceU was introduced in 1959 as a high-performance primary cell to replace the Leclanche (carbon-zinc) cell that was developed by Georges Leclanche in 1860 and is still the battery of choice in the developing countries because of its low cost. The zinc chloride cell was introduced... 

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. 

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 ordinary Leclanchd cell uses a mixture of ammonium chloride and zinc chloride, with the former predominating. Zinc-chloride cells typically use only Z11CI2, but can contain a small amount of NH4CI to ensure high rate performance. Eixamples of typical electrolyte formulation for the zinc-carbon battery systems are listed in Table 8.3. 

The effect of temperature on the available capacity of zinc-carbon (Leclanch6 and zinc-chloride systems) batteries is shown graphically in Fig. 8.28 for both general-purpose (ammonium chloride electrolyte) and heavy-duty (zinc-chloride electrolyte) batteries. At — 20°C typical zinc-chloride electrolytes (25% to 30% zinc-chloride by weight) turn to slush. Below -25°C ice formation is likely. Under these conditions, it is not surprising that performance is dramatically reduced. These data represent performance at flashUght-type current drains (300 mA for a D-size cell). A lower current drain would result in a higher capacity than shown. Additional characteristics of this D-size battery at various temperatures are listed in Table 8.7. 

Zinc-carbon batteries are made in a number of different sizes with different formulations to meet a variety of applications. The single-cell and multicell batteries are classified by electrochemical system, either Leclanche or zinc chloride, and by grade general purpose, heavy duty, extra heavy duty, photoflash, and so on. These grades are assigned accortUng to their output performance under specific discharge conditions. 

Table 8.11 lists some of the major multicell zinc-carbon batteries that are available commercially. The performance of these batteries can be estimated by using the lEC designation to determine the cell compliment (e.g. NEDA 6, lEC 4R25 battery consists of four F-size cells connected in series). Table 8.12 gives cross-references to the zinc-carbon batteries and manufacturer s designations. The most recent manufacturer s catalogs should be consulted for specific performance data to determine the suitability of their product for a particular application. 

Figure 38.17 is a side view of a flat-pack cell. Figure 38.18 compares the performance of a 6-V four-cell hybrid lantern battery with similar alkaline and zinc-carbon batteries at an intermittent low-rate discharge. The specific energy of this battery is about 350 Wh/kg. Single and multicell batteries are available in capacities of 40 to 4800 Ah. 

Carbon can be used [7,11,62,70—73] as an electrocatalyst for the O2 reduction in alkaline electrolytes (compare also section 5 in chapter VIII). The performance which is not so good as that of silver (see Fig. 79) appears adequate for certain purposes, for instance, in small zinc-air cells. Activation procedures [72,73] which are not of an electrochemical nature improve the performance of carbon oxygen electrodes. The performance rapidly becomes poor with decreasing pH below pH <14. In acid solution, the impregnation of carbon with platinum metals or other electrocatalysts is required. The data [73] in Table 8... 

The zinc chloride cell performs better at low temperatures than the standard carbon-zinc cell. Figure 30.37(b) indicates the variation of service capacity with temperature for a D-size zinc chloride cell discharged on the 2.25 Q light-industrial flashlight test. The load simulates a 0.5 A lamp,... 

The performance and capacity advantages of alkaline batteries vs carbon—zinc is resulting in the continuous decline of this battery. The low cost of the carbon zinc cell is a major reason for its continued use. Thus, cost is a major consideration in the development and selection of separators for this system. 

Performance. Carbon-zinc cells perform best under conditions of intermittent use, and many standardized tests have been devised that are appropriate to such applications as light and heavy flashlight usage, radios, cassettes, and motors (toys). The most frequently used tests are American National Standards Institute (ANSI) tests. The tests are earned out at constant resistance and the results reported in minutes or hours of service. Figure 1 shows typical results under a light load for different size cells. 

Most battery systems employ carbon materials in one form or another, as noted in Table 10.1. The use of carbon materials in batteries stretches across a wide spectrum of battery technologies. The variety of carbon runs the gamut from bituminous materials, used to seal carbon-zinc and carbon black powders in lead acid batteries, to high performance synthetic graphites, used as active materials in lithium-ion cells. The largest use is as a conductive diluent to enhance the performance of cathode materials. In many instances, it is used as a conductive diluent for poorly conducting cathode materials where carbon blacks, such as acetylene black, are preferred. It is essential that... 

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