Battery separators zinc-manganese

For battery separators, regenerated cellulose is placed on the surface of nonwoven so that the nonwoven is available to promote the wicking of the electrolyte. The nonwovens should not allow the penetration of viscose into itself. Suitable nonwovens are made from polypropylene, poly(vinyl alcohol), and hardwood hemps. Regenerated cellulose films are commonly used in alkaline manganese cells, both primary and secondary, in NiCd industrial batteries, as well as in silver—zinc batteries. 

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... 

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. 

As discussed in previous chapters, the separators are an integral part of liquid electrolyte batteries including nonaqueous batteries such as lithium-ion, lithium-polymer, hthium-ion gel polymer, and aqueous batteries such as zinc-carbon, zinc-manganese oxide, lead-acid, nickel-based batteries, and zinc-based batteries. 

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 ... 

In Figure 44 an overall mass balance based on production-scale illustrates the flow of the materials recovered in the process [61]. Important steps of the overall Recytec Process for battery recycling are as follows pyrolysis and gas treatment (condensation), shredding and washing, magnetic-inductive separation and electrolysis of the non-ferrous scrap and magnetic separation followed by the electrolysis of manganese dioxide and zinc. 

An alkaline battery is also based on the reduction of manganese dioxide and the oxidation of zinc. However, the reactions take place in a basic medium, hence the name alkaline battery. The anode consists of powdered zinc suspended in a gel. which is in contact with a concentrated solution of KOH. The cathode is a mixture of manganese dioxide and graphite. The anode and cathode are separated by a porous barrier (Figure 19.7). 

Figures 11J5 and 11.16 illustrate two designs of Leclanche battery. The first shows the traditional cylindrical design. The negative zinc electrode is a zinc lining to the metal can which is amalgamated with mercury to minimize hydrogen gas formation by reaction of the metal with water the separator is a paper stiffened with cellulose or starch placed adjacent to the zinc can. The positive current collector is a carbon rod at the centre of the can, while most of the volume is taken up by the positive paste. This is a mixture of powdered manganese dioxide ainmotmtm chloride and acetylene black (carbon) to increase the conductivity the pores are filled with an aqueous electrolyte (NH Cl + ZnCl ) gelled by addition of starch. The can is totally scaled.

Alkali-manganese and zinc-carbon batteries (up to a maximum of 100 ppm Hg) are melted together with other preliminary materials. The zinc is reclaimed during the gaseous phase and thus permanently separated from most of the accompanying elements (Figure 19.15). 

Industrial Heavy Duty. Application Intermittent medium- to heavy-rate discharges, low to moderate cost. The industrial heavy-duty zinc-carbon battery generally has been converted to the zinc chloride system. However, some types continue to include ammonium chloride and zinc chloride (ZnCl2) as the electrolyte and synthetic electrolytic or chemical manganese dioxide (HMD or CMD) alone or in combination with natural ore as the cathode. Its separator may be of starch paste but it is typically a paste-coated paper liner type. This grade is suitable for heavy intermittent service, industrial applications, or medium-rate continuous discharge. 

Industrial Heavy Duty. Application Low to intermediate-continuous and intermittent heavy-rate discharges low to moderate cost. This battery has generally replaced the industrial Leclanch6 heavy-duty battery. It is a true zinc-chloride cell and possesses the heavy-duty characteristics of the premium zinc chloride type. The cell electrolyte is zinc chloride however, some manufacturers may add small amounts of ammonium chloride. Natural manganese dioxide ore is used along with electrolytic manganese dioxide as the cathode. These cells use paper separators coated with cross-linked or modified starches, which enhance their stability in the electrolyte. Batteries of this formulation and design are competitive in cost to the Leclanche heavy-duty industrial batteries. They are recommended for heavy-duty applications where cost is an important consideration. This battery also exhibits a low le age characteristic. 

The manganese dioxide is mixed in a slurry which contains the electrolyte salts. The electrolyte is mainly zinc chloride with some ammonium chloride. The anode and the cathode are separated by a thin film of cellophane. The complete 6-volt battery has four cells. The four identical cells are connected by vinyl frames to each other and the aluminum collector plates. A special conductive coating allows the aluminum to bond to the plastic materials. 

Figure 13.3 shows a magnified cross-sectional view of the cathode region of the zinc/air battery. The cathode structure includes the separators, catalyst layer, metallic mesh, hydro-phobic membrane, diffusion membrane, and air-distribution layer. The catalyst layer contains carbon blended with oxides of manganese to form a conducting medium. It is made hydro-phobic by the addition of finely dispersed Teflon particles. The metallic mesh provides structural support and acts as the current collector. The hydrophobic membrane maintains the gas-permeable waterproof boundary between the air and the cell s electrolyte. The diffusion membrane regulates gas diffusion rates (not used when an air hole controls gas diffusion). Finally the air distribution layer distributes oxygen evenly over the cathode surface. 

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