Discharging alkaline-manganese dioxide cells

The design of a AA-size alkaline manganese dioxide cell is shown in Fig. 1 (Sec. 3.1). Primary and secondary alkaline batteries are constructed in the same way and can be manufactured on essentially the same machinery. The separator material, electrode formulation, and the Mn02 Zn balance are different. Rechargeable cells are zinc-limited to prevent a discharge beyond the first electron-equivalent of the MnOz reduction. The electrolyte is 7-9 mol L KOH. The electrode reactions are ... 

FIGURE 36.10 First cycle discharge characteristics of rechargeable zinc/alkaline/manganese dioxide AAA-size cells discharged continuously at different constant resistance loads at 20°C. Curve 1 - 10 11. 110 mA (approx.) curve 2 - 5.1 H. 190 mA (approx.) curve 3 - 3.9 H. 260 mA (approx.). (Courtesy of Battery Technologies Inc.)... 

Figure30.56 1, SAFT LC01 1.5 V (3.6Ah) lithium-copper oxide cell 2, alkaline K6 zinc-manganese dioxide cell. Capacity versus discharge current at various operating temperatures. The superiority of the lithium-copper oxide couple at low drain is evident (Courtesy...

Zinc-Manganese Dioxide Batteries. The combination of a zinc anode and manganese dioxide cathode, which is the dominant chemistry in large cylindrical alkaline cells, is used in some miniature alkaline cells as well. Overall, this type of cell does not account for a huge share of the miniature cell market. It is used in cases where an economical power source is wanted and where the devices can tolerate the sloping discharge curve shown in Figure 2. 

Zn(OH)2 is soluble in the alkaline solution as [Zn(OH)3]- until the solution is saturated with K[Zn(OH)3]. In addition Zn(OH)2 can be dehydrated to ZnO. An enhanced power density (when compared with the - Leclanche cell) is accomplished by using particulate zinc (flakes) soaked with the alkaline electrolyte solution. This anode cannot be used as a cell vessel like in the Leclanche cell. Instead it is mounted in the core of the cell surrounded by the separator the manganese dioxide cathode is pressed on the inside of the nickel-plated steel can used as battery container. In order to limit self-discharge by corrosion of zinc in early cells mercury was added, which coated the zinc effectively and suppressed hydrogen evolution because of the extremely low exchange current density... 

Unlike some other cathode materials, such as manganese dioxide, which are quite insoluble, silver oxide has a fair degree of solubility in alkaline electrolyte. If the soluble silver species were allowed to be transported to the zinc anode it would react directly with the zinc, and as a result the cell would self-discharge. In order to prevent this from happening, zinc—silver oxide cells use special separator materials such as cellophane [9005-81-6], that are designed to inhibit migration of soluble silver to the anode. 

The zinc and manganese dioxide electrode reaction kinetics in alkaline electrolyte are faster than the same reactions in the Leclanche and zinc chloride electrolyte. These differences in reaction rate determine the differences in cell performance. The alkaline cell delivers superior capacity, higher-rate discharge capability, lower internal resistance, lower leakage, and longer shelf life. Alkaline cells have excellent high-rate... 

The alkaline cell has an open-circuit voltage of 1.5 V that can deliver 150 Wh/kg and 460 Wh/1. The reactions have fast kinetics and can deliver full capacity, even at high-rate discharges. Since its introduction in 1959, there has been a steady increase in performance of the alkaline cell as new materials and cell components were incorporated into the structure. The present alkaline cell designs are based on the use of nanostructured electrolytic manganese dioxide, a thinner polymer gasket seal with sealant to increase internal volume and improve shelf Ufe. Mercury has been eliminated by using new zinc alloy compositions. These improvements have resulted in about a 40 % improvement in performance over the same-size cells produced in 1959. 

The alkaline cell competes against the lower-cost carbon-zinc cells. Figure 6 compares the performance of the D-size and AA-size Leclanche (carbon-zinc) cell with the same-size alkaline cell on various discharge rates at 21 °C (70 °F). The superior performance of the alkahne ceU at all discharge rates is clear. Since both systems use zinc and manganese dioxide chemistry, the shape of the discharges are similar. 

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