Electrodes flat-plate construction

Another popular electrode design in the flat-plate construction, typically used in the lead-acid SLI and most larger storage batteries (Fig. 3.21c). This constraction also provides a large surface area for the electroehemical reaction. As with the other designs, the manufacturer can control the relationship between surface area and active material (for example, by controlling the plate thickness) to obtain the desired performance characteristics. 

Flat plates or concentric cylinders may be utilized in the construction of an ionization chamber. The flat plate design is preferred because it has a well-defined active volume and ensures that ions will not collect on the insulators and cause a distortion of the electric field. The concentric cylinder design does not have a well-defined active volume because of the variation in the electric field as the insulator is approached. Ionization chamber construction differs from the proportional counter (flat plates or concentric cylinders vice a cylinder and central electrode) to allow for the integration of pulses produced by the incident radiation. The proportional counter would require such exact control of the electric field between the electrodes that it would not be practical. 

As with previous methods, artificially layered deposits may be obtained from a single chemical solution using a specially designed cell, for instance, with adjustable anode-cathode gap (see Fig. 17.3). This two-compartment cell may be constructed from Lucite with deposition conducted in one compartment, and KC1 solution placed in the other. A calomel reference electrode immersed in this KC1 solution should be coupled to the flat-plate cathode by a salt bridge, ending in a capillary on the deposition side. The specimen electrode is fixed, and the counter-electrode is movable using, say, a micrometer. Electrodeposition is best conducted under quiescent conditions. 

Fig. 8.3 General overview of the various processes that constitute the processes for manufacturing Li-Ion cells, starting with the coating operations for piepEiring the electrode stock. More specific manufacturing operations follow for the assembly of the cylindrical, prismatic tind flat plate/laminate cell constructions...

The construction of flat-plate prismatic cells is illustrated in Fig. 35.35. As in a wound cell, a microporous polyethylene or polypropylene separator separates the positive and negative electrodes. Typically each plate in the cell has a tab, the tabs are bundled and welded to their respective terminals or to the cell case. Cell cases of either nickel-plated steel or 304L stainless steel have been used. As shown, the cover typically incorporates one or two terminals, a All port and a rupture disk. The terminal may be a glass-to-metal seal, for low cost applications compression type seals have been used, or the terminal may incorporate devices similar to those found in the header of cylindrical products to provide pressure, temperature and over current interrupt in one component. The case to covo" seal is typically formed either by TIG or laser welding. 

This type of battery has a spiral-wound electrode pack, made from rectangular foil electrodes. Lithium foil is rolled on to an expanded metal mesh current collector as the negative electrode, and is separated from the similarly supported cathode by a polypropylene separator. Two types of cell construction are used jelly-roll electrodes in crimp-sealed or hermetically sealed cylindrical cells, and large 20-100Ah 12V flat-plate electrodes in large reserve batteries. It is a relatively high-pressure system and cells must have salety vents to avoid explosion in the event of accidental incineration (see Part 2 for further details of construction). 

Two typical cell constructions are used jelly-roll electrodes in crimp sealed on hermetically sealed cylindrical cells, and large 20-100Ah, 12 V flat-plate electrodes in large reserve batteries. 

This company have constructed a number of cells with energies from 20 to 1300Wh. Tubular and flat plate bipolar electrodes were studied. 

Planar SOFCs are composed of flat, ultra-thin ceramic plates, which allow them to operate at 800°C or even less, and enable less exotic construction materials. P-SOFCs can be either electrode- or electrolyte- supported. Electrolyte-supported cells use YSZ membranes of about 100 pm thickness, the ohmic contribution of which is still high for operation below 900°C. In electrode-supported cells, the supporting component can either be the anode or the cathode. In these designs, the electrolyte is typically between 5-30 pm, while the electrode thickness can be between 250 pm - 2 mm. In the cathode-supported design, the YSZ electrolyte and the LSM coefficients of thermal expansion are well matched, placing no restrictions on electrolyte thickness. In anode-supported cells, the thermal expansion coefficient of Ni-YSZ cermets is greater than that of the YSZ... 

The enclosed strip apparatus requires more skillful construction, because the cooling plate on which the filter paper sheet is positioned must be manufactured with a uniform flatness to achieve a precision within 0.002 mm [11,12]. The plate itself is usually made of aluminium and the filter paper sheet is uniformly pressed to it during separation by a pressure of about 1 atm/cm. Cooling is effected by tap water running through the labyrinth of channels of the cooling plate. Buffer vessels are placed at each end of the plate and are equipped with screened platinum electrodes. Contacts between the filter paper sheet on the plate and electrode vessels is materialized by means of thick filter paper wicks (Whatman 3 MM) moistened with the buffer solution. The filter paper sheet is not positioned directly on the cooling plate, but is isolated from both sides by a polyethylene insulation foil. 

The flat cell is illustrated in Fig. 8.5. In this construction, a duplex electrode is formed by coating a zinc plate with either a carbon-filled conductive paint or laminating it to a carbon-filled conductive plastic film. Either coating provides electrical contact to the zinc anode, isolates the zinc from the cathode of the next cell, and performs the function of cathode collector. The collector function is the same as that performed by the carbon rod in cylindrical cells. When the conductive paint method is used, an adhesive must be placed onto the painted side of the zinc prior to assembly to effectively seal the painted surface directly to the vinyl band to encapsulate the cell. No expansion chamber or carbon rod is used as in the cylindrical cell. The use of conductive polyisobutylene film laminated to the zinc instead of the conductive paint and adhesive usually results in improved sealing to the vinyl however, the film typically occupies more volume than the paint and adhesive design. These methods of construction readily lend themselves to the assembly of multi-cell batteries. 

Pocket Plate Electrode. This is the same type of electrode used in pocket plate nickel-cadmium and nickel-iron batteries. Electrodes are prepared by loading nickel hydroxide hydrate active material and a conductive additive (graphite and/or nickel flake) into tubular flat pockets which are then assembled into electrodes. Little interest currently exists in using this type of electrode in nickel-zinc cells since modern cells attempt to utilize lightweight electrode construction. 

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