Zinc-Carbon Batteries Leclanche Cells

Zinc-carbon is one of the oldest cell technologies still on the market today, dating back over 100 years. These batteries are suitable for moderately low-drain application and, as such, have a steady market in small consumer electronics such as flashlights and portable radios. They are among the least expensive and are sold as Heavy Duty cells. 

The Leclanche cell contains a zinc anode, aqueous ammonium chloride electrolyte, and manganese dioxide cathode. Carbon (acetylene black) is mixed 

In cases of forced overdischarge or accidental charging, both of these abuse conditions can lead to electrolysis of water within the cell to create a hydrogen/oxygen gas mixture. Proper venting of the cell can relieve internal pressure, but the explosive gas mixture can pose a risk to the immediate area until the gas dissipates. Accidental charging can also lead to evolution of highly toxic chlorine gas (in the case of zinc-chloride types). 

Finally, since the battery container is typically made from the zinc which also serves as the anode, as the cell discharges and the zinc metal is oxidized, the metal container becomes thiimer, thereby increasing the risk of leakage. 

---

ZINC-CARBON BATTERIES (Leclanche and Zinc Chloride Cell Systems) ... 

A common dry cell battery is the zinc-carbon battery, using dry Leclanche cell, with a nominal voltage of 1.5 volts. 

Describe the zinc—carbon, or Leclanche, dry cell and the lead storage battery. 

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. 

Closed-Circuit Voltage. The closed-circuit voltage (CCV), or working voltage, of the zinc-carbon battery is a function of the load or current drain the cell is required to deliver. The heavier the load or the smaller the circuit resistance, the lower the closed-circuit voltage. Table 8.4 illustrates the effect of load resistance on the closed-circuit voltage for D-size batteries in both the Leclanche and zinc-chloride systems. 

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. 

The electrolyte was a solution of ammonium chloride that bathed the electrodes. Like Plante s electrochemistry of the lead-acid battery, Leclanche s electrochemistry survives until now in the form of zinc-carbon dry cells and the use of gelled electrolyte.12 In their original wet form, the Leclanche electrochemistry was neither portable nor practicable to the extent that several modifications were needed to make it practicable. This was achieved by an innovation made by J. A. Thiebaut in 1881, who through encapsulating both zinc cathode and electrolyte in a sealed cup avoided the leakage of the liquid electrolyte. Modern plastics, however, have made Leclanche s chemistry not only usable but also invaluable in some applications. For example, Polaroid s Polar Pulse disposable batteries used in instant film packs use Leclanche chemistry, albeit in a plastic sandwich instead of soup bowls.1... 

Leclanche cells are the least expensive primary batteries. The first zinc-manganese dioxide cell was developed by Georges Leclanche in 1866. He developed the primary battery with an ammonium chloride and zinc chloride electrolyte, and with a natural Mn02 and carbon (usually acetylene black) cathode inserted into a zinc can. His name is still associated with this chemistry today. The battery reactions are given in Equation 10.1. 

FIGURE 10.3 Construction of the carbon-zinc cells. The zinc chloride and Leclanche have the same construction except for the seal. The zinc chloride has a plastic-compression seal while the Leclanche has a poured hot bituminous seal instead of the plastic-compression seal shown. (Courtesy of Eveready Battery Co., St Louis, MO. With permission.)... 

Camacho cell — This was a - chromic acid battery with zinc anodes, and a construction that the chromic acid solutions flowed through the cathode compartment housing the inert carbon electrodes. See also - Daniell cell, - zinc, - Zn2+/Zn electrodes, - Zn2+/Zn(Hg) electrodes, - zinc-air batteries (cell), and - Leclanche cell. Ref [i] Hauck WP (1883) Die Galvanischen Batterien, Accumulatoren und Thermosaulen, 2nd edn. Hartleben s Verlag Wien... 

See also - Leclanche cell, -> Zn2+/Zn electrodes, -> Zn2+/Zn(Hg) electrodes, -> zinc-air batteries (cell), -> zinc-carbon cell, -> zinc electrowinning. 

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. 

---