Cell voltage zinc chloride

Electrode polarization of the anode is less severe than that for the cathode and is mainly concentration polarization resulting from accumulation of zinc chloride near the electrode surface. During rest periods after discharge, diffusion of ZnCl2 into the bulk of the electrolyte reduces the anode polarization and this also contributes to the recovery of the cell voltage. Polarization behaviour of the cathode and anode of a D-size Leclanche cell is shown in Fig. 3.7. 

The alkaline manganese dioxide cell is most widely available either as standard sized cylindrical cells with capacities ranging from 0.6 to 22 Ah or as button cells. Batteries having a wide variety of capacities and voltages are also readily available. These are all interchangeable with Leclanche and zinc chloride cells. 

Carbon-zinc is the generic term for the Leclanche and zinc chloride system. Carbon-zinc cells provide an economical source of electrical energy for low drain applications. The service life depends strongly on the discharge rate, the operating schedule and the cutoff voltage, as well as temperature and storage conditions. 

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. 

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 chloride cells are able to operate at higher electrode efficiencies than carbon-zinc cells and hence have a higher useful current output and will operate at higher current drains than carbon-zinc cells of the same size. In addition, the voltage lever under load... 

Figure 30.37 Effect ot temperature onthe capacity of D-sized ceils (a) carbon-zinc dry cells discharged conlinuouslythrough a resistance of 2.25 c to an end-voltage of 0.9 V (b)zinc chloride cells when discharged 4min, 1 h, 8h, 1 day with a 16h rest through a resistance of 2.25 n to a cut-off voltage of 0.9 V (Courtesy of Union Carbide)...

Types of activated carbon which have electrical conductivity can be used instead of manganese dioxide as a depolarizer in dry-cell batteries.77 Powdered activated carbon is treated with ammonium chloride and pressed into a porous cylindrical shape that is placed in a zinc container forming the outer electrode. If provision is made for a sufficient. supply of air, the effect of the activated carbon cylinder is similar to that of"manganese dibxide. The potential of the activated carbon batter is 0.1 volt lower than that of the manganese dioxide type, but the voltage is steadier and is practically constant throughout the life of the battery. 

SAFT lithium-thionyl chloride cells exhibit a highly stable service voltage and a far greater capacity than conventional zinc-manganese dioxide and carbon-zinc cells of the same size and configuration. 

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