Zinc-carbon batteries separators

Accurate sorting relies on the identification of a number of different properties of a battery. These include the physical size and shape, the weight, the electromagnet properties and any surface identifiers such as colour or unique markings. These properties can be analysed in a number of different combinations in order to sort batteries into nickel cadmium, nickel metal hydride, lithium, lead acid, mercuric oxide, alkaline and zinc carbon batteries. Due to an voluntary marking initiative introduced by the european battery industry, it is now also possible to separate the alkaline and zinc carbon cells further into mercury free and mercury containing streams. 

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). 

During this transitional phase, the zinc-carbon batteries can be classified into two types, Leclanche and zinc chloride. These can, in turn, be subdivided into separate general purpose and premium battery grades, in both pasted and paper-lined constructions ... 

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. 

Zinc-carbon batteries are commonly used, and the separators for these batteries are gelled paste and paper coated with gelling agents. 

Dry cells have been well-known for over 100 years and form the technical basis of today s modern dry cell industry. Zinc carbon cells are the most widely used of all the primary batteries worldwide because of their low cost, availability, and acceptability in various situations. The two major separator types ever used or in use are gelled paste and paper coated with cereal or other gelling agents such as methyl-cellulose. The paste type is dispensed into the zinc can, and the preformed bobbin is inserted, pushing the paste up the can walls between the zinc and the bobbin. A typical paste electrolyte uses zinc chloride, ammonium chloride, water, and starch or flour as the gelling agents. The coated-paper type uses a special paper coated with flour, starch, regenerated cellulose. 

Anaiyze and Conciude Zinc-carbon, alkaline, mercury, lithium, and NiCad batteries all contain a separator between the anode and cathode that allows exchange of ions but keeps the anode and cathode reactants from mixing. No such separator is present (or needed) in a lead-acid battery. 

The remaining batteries are fed into a charging hopper which feeds a pocketed belt conveyor. This in turn deposits the batteries onto a cascade of sieves which have been carefully selected to remove dust and button cells. The remaining batteries are then fed onto a wide band conveyor which passes beneath a magnetic over-band conveyor which separates the magnetic fraction from the paper jacketed zinc carbon cells and batteries. 

In the zinc-carbon dry cell, a spacer made of a porous material and damp from the liquid in the paste separates the paste from the zinc anode. The spacer acts as a salt bridge to allow the transfer of ions, much like the model voltaic cell you studied in Section 20.1. The zinc-carbon dry cell produces a voltage of 1.5 V until the reduction product, ammonia, comes out of its aqueous solution as a gas. At that point, the voltage drops to a level that makes the battery useless. 

Figure 1.39 shows the principle of the zinc/bromine battery. In Fig. 1.39, the cell stack consists of only three cells. Actual batteries contain stacks of 50 or more cells. Except the two end plates, all electrodes are bipolar. They consist of an electron-conducting plate of carbon plastic enframed by insulating plastic. On the positive side, a porous layer of carbon increases the surface to increase the reaction rate of bromine. In the center of each cell, a microporous separator is positioned as used in lead-acid batteries (e.g. Daramic ) to suppress the direct contact between bromine and zinc as far as possible. 

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. 

Conventional Systems. Reserve batteries employing the conventional electrochemical systems, such as the Leclanch6 zinc-carbon system, date back to the 1930-1940 period. This stmcture, in which the electrolyte is kept in a separate vial and introduced into the cell at the time of use, was employed as a means of extending the shelf life of these batteries, which was very poor at that time. Later similar stmctures were developed using the zinc-alkaline systems. Because of the subsequent improvement of the shelf life of these primary batteries and the higher cost and lower capacity of the reserve stmcture, batteries of this type never became popular. 

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. 

Button cells consist of cathode and anode cans (used as the terminals), powdered zinc anode, containing gelled electrolyte and the corrosion inhibitor, separator with electrolyte, thin (0.5 mm) carbon cathode with catalyst and PTFE, waterproof gas-permeable (teflon) layer and air distribution layer for the even air assess over the cathode surface. Parameters of battery depend on the air transfer rate, which is determined by quantity and diameters of air access holes or porosity of the gas-diffusion membrane. Air-zinc batteries at low rate (J=0,002-0,01C at the idle drain and J= 0,02-0,04C at the peak continuous current) have flat discharge curves (typical curve is shown by Figure 1). 

The performance and capacity advantages of alkaline batteries vs carbon—zinc is resulting in the continuous decline of this battery. The low cost of the carbon zinc cell is a major reason for its continued use. Thus, cost is a major consideration in the development and selection of separators for this system. 

Bunsen cell - Bunsen replaced the platinum electrode in the -> Grove cell by a - carbon electrode [i]. The Bunsen battery contained a zinc electrode in sulfuric acid and a carbon electrode in nitric acid. The two electrode compartments were separated by a ceramic pot. Bunsen discovered a way to carbonize a mixture of powdered coke and hard coal by strong heating thus foreshadowing the later used graphitizing process [ii, iii]. 

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. 

The second battery (Fig. 10.17) is a series of six cells with bipolar (or duplex) electrodes. Each cell has the same components as the first cell, i.e. zinc can, separator, positive paste and carbon current collector. The latter is not a carbon rod but the bottom face of the duplex electrode. The whole set of cells is sealed in wax. In both cells the zinc electrode rapidly develops porosity as the corrosion process occurs while the performance is largely determined by the quality of... 

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