D-size cells

The connection of AA-size cells in parallel can replace larger cells (e.g., D-size cells). Four AA cells fit into a D-size can, and six AA-cells are in equivalent weight to a D-cell [27]. The utilization of the Mn02 cathode is considerably improved because the cathode thickness is only 2 mm in a AA cell, but 5 mm in a D-cell. The internal resistance is also lower by a factor of 4 to 6. Figure 11 depicts a 5 PxlO S bundle battery five AA cells in parallel = 1 bundle, 10 bundles in series make a (nominal) 12 V battery. It is used as the power source for a transmitter/receiver service. A typical load profile is 2 A for 1 min, 0.33 A for 9 min average load, 0.5 A per bundle or 0.1 A per cell service, about 15 h. Smaller bundle batteries (with 2x9 cells) are very suitable for notebook-computers 18 AA cells weight 0.36 kg, and the total initial capacity is 32 Wh. 

The effect of discharge rate is shown in Figs 3.13 and 3.14 where closed circuit voltage characteristics and service life of D-size cells are shown as a function of current drain. The fact that service life increases as current density decreases suggests that for this type of system it is always best to use as large a cell as possible. It has been estimated that over a wide range of current densities, the service life is tripled by halving the current density. 

The service schedule is of critical importance in relation to the recuperation reaction. Unless the current drain is ver low, Leclanchd cells give a much better performance when used on an intermittent basis. The effect of rest periods was shown earlier in Fig. 3.5. In Fig. 3.15 the effect on the service life of D-size cells of two different operating schedules is illustrated. A schematic three-dimensional representation of capacity as a function of current drain and operating programme based on Union Carbide technical data is given in Fig. 3.16. 

D-size cells on 2.25 O continuous test are reported. Cell (a) is a standard Leclanchd cell using a natural ore cell (b) is a HD Leclanche with electrolyte Mn02 cell (c) is a zinc chloride cell and cell (d) is an alkaline manganese primary unit. The differences at this current drain are striking the discharge capacities with a 0.9 V cut-off are in the ratio 0.12 0.24 0.55 1.00 for the four types. However, when less severe tests are considered, the disparities are less pronounced. Thus for the light industrial flashlight (LIF) test, the ratios are 0.40 0.61 0.96 1.00. 

The most obvious advantages of the oxygen cathode are that it has low weight and infinite capacity. Consequently, prototype D-size cells based on the zinc-air system have been shown to have twice the overall practical capacity of zinc-mercuric oxide cells (and 10 times that of a standard Leclanchd cell) when subjected to a continuous current drain of 250 mA. In the larger industrial cells, energy densities of up to 200 Wh/kg and specific capacities of 150 Ah/dm3 may be obtained. On the other hand, a catalytic surface must be provided for efficient charge transfer at the oxygen cathode, and by its nature the electrode is susceptible to concentration polarization. 

At room temperature, discharge curves are exceptionally flat (Fig. 4.35), even at rates of up to 3 A for D-sized cells. As noted above, SOCl2 utilization is much higher at low current drains. Low rate cells manufactured by Mallory with a spiral configuration (4.45 cm X 25-38 cm electrodes) produced practical energy densities of 661 Wh/kg (1240 Wh/dm3)... 

The energy density of liquid cathode lithium cells can be further enhanced to over 500 Wh/kg (1000 Wh/dm3) by the use of halogen additives. BrCl, added to lithium-thionyl chloride cells, boosts the OCV to 3.9 V and prevents the formation of sulphur in the early stages of discharge. D-sized cells are manufactured, Addition of chlorine to lithium-sulphur yl chloride cells increases the energy density and improves the temperature-dependent electrical characteristics. 

Performance. Carbon—zinc cells perform best under 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 (6). The tests are carried out at constant resistance and the results reported in minutes or hours of service. Figure 3 shows typical results under a light load for different size cells, whereas Figure 4 shows results for different types of R20 "D"-size cells under a heavy intermittent load. 

C, on relative discharge performance of fresh and aged "D"-size cells on Le—manganese, and (b) carbon—zinc batteries (22). 

Figure 1. Comparison of discharge characteristics of alkaline Mn02-Zn and Leclanche D-size cells for SOOmA starting, discharged continuously at 21°C.

Figure 12. Capacity of typical Mn02 Zn cells (C and D size cells) at various temperatures under high and low discharge load. Without Hg the high-load curves (300 and 500 mA) will drop about 50 % at -10°C.

Table 4 shows the internal resistance of fresh, undischarged alkaline Mn02-Zn cells. Datas are given for AA, C and D size cells at various temperatures [35,36], Without mercury the internal resistance at -10°C is expected to double. 

Internal resistance of AA, C and D size cells versus temperature... 

By 1986 C and D size cells were developed to the point that 50 deep discharge cycles (100 % DOD) to 50 % of the original capacity and 250 shallow discharge cycles (10 % DOD) were reached. Figure 15 shows the construction of the C size and D size cell respectively [10,37]. The cumulative capacity of the C cells at that time ranged, depending on the depth of dscharge (DOD), from 75 to 150 Ah. 

Figure 25. Discharge capacity of 1 D size cell and arrays of 4 AA and 7 AAA size cells (4 Q load).

Figure 26. Comparison of the discharge of 1 D size cell and a parallel array of 6 AA cells.

The better efficiency and the more evenly utilization of the Mn02 cathode in bundle cells lowers the loading per cell and leads to an improved cycle life. But if required, the cell can also supply very high currents for special applications, e g. hand tools, video cameras, portable TV s and wheelchairs. Figure 29 shows how the change from I D size cell to a multi-cell... 

The alkaline Zn-Mn02 cell has higher capacity compared to the cells with Leclanche and zinc chloride electrolyte. In the D-size cell configuration, it can deliver about 15 Ah compared to about 7 Ah for the zinc chloride cell and 5 Ah for the Leclanche or carbon-zinc version. In addition, the zinc chloride and Leclanche versions exhibit a significant fall off in capacity on higher-rate discharges. 

Alkaline cells are available worldwide in a variety of sizes and shapes. The term alkaline ceU is used to describe the specific cell containing zinc aUoy powder anode, nanostmc-tured electrolytic manganese dioxide cathode, and concentrated potassium hydroxide (KOH) electrolyte. The construction of the D-size cell is given in Fig. 1 and is typical of the constmc-tions of all alkaline cylindrical cells from the... 

FIGURE 8.18 Comparison of Leclanche and zinc-chloride D-size cells of various grades discharged on the ANSI LIF test (4 min/h, 8 h/day) through 2.2 ohm at 20 C. GP-general purpose HD-heavy duty EHD-extra heavy duty. 

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. 

FIGURE 14 27 Capacity retention of spirally wound Li/SOClj D-size cell, storage at 20 C. Courtesy of SAFT America, Inc.)... 

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