Sintered plate electrodes

Cell construction is mainly confined to two types, using either pocket plate electrodes (vented cells) or sintered , bonded or fibre plate electrodes (vented and sealed cells). In the former, the active materials are retained within pockets of finely perforated nickel-plated sheet steel which are interlocked to form a plate. Positive and negative plates are then interleaved with insulating spacers placed between them. In sintered plate electrodes, a porous sintered nickel mass is formed and the active materials are distributed within the pores. In sintered plate vented cells, cellulose or other membrane materials are used in combination with a woven nylon separator. In sealed or recombining cells, special nylon separators are used which permit rapid oxygen diffusion through the electrolyte layer. 

Iron-nickel oxide cells are always vented. Tubular/pocket plate electrodes are constructed as described above and are generally housed in nickel-plated steel cases. Cells with sintered plate electrodes have smaller inter-electrode spacings. They use synthetic fibre fabrics as separators, and plastic containers. 

Unlike the pocket-plate electrodes, the sintered-plate electrodes do not need the addition of any conductive material (such as graphite) to create enough electronic conductivity of the electrode, because plaque itself provides this function. On the other hand, the sintered-plate electrodes do not need the addition of the binder material to the active material to create the structural integrity of the electrode, because the plaque itself provides this integrity in the first place. Having these structural advantages, the sintered-plate... 

FIGURE 28.13 Resistance vs. state of charge at 20°C, discharged at 0.2C rate, for sealed nickel-cadmium batteries, a—AA-size battery, b—sub-C-size battery. (Typical for sintered-plate electrode type batteries.)... 

Energy densities currently being achieved are 20-30 Wh/kg (tubular plate electrodes) and 40-60Wh/kg (sintered plate electrodes). The positive plate comprises thick sintered nickel plates on a nickel plated substrate. The negative plate comprises a mixture of powdered iron and Fe30a. The electrolyte contains 1.2 to 1.3g/cm potassium hydrioxide containing 1-2% lithium hydroxide. The cells are vented. Synthetic fibres are used for separators. 

Sintered plate electrodes suitable for high-rate discharge and trickle charge ... 

Pocket and tubular electrodes have been described in detail by Falk and Salkind [1]. McBreen has reviewed work on both sintered plate and plastic-bonded electrode technology [9], More recent work is on the use of nickel foams and nickel mats. 

It is probable that a range of soluble species such as Fe(OH)2 and Fe02 are involved, and it is known that Fe(OH)3 or Fe304 may be formed on deep discharge. The practical energy density of conventional tubular plate cells is 20-30 Wh/kg with the more recent cells which use press-sintered iron electrodes, values of 40-60 Wh/kg have been reported. 

After the sintering stage, electrodes are applied, usually either by electroless nickel plating or by painting or screening on specially adapted silver paint. Leads are then soldered to the electrodes when, for many applications, the device is complete in other cases it may be encapsulated in epoxy or silicone resins. Examples are illustrated in Fig. 4.15. 

The thermodynamics of disproportionation can be readily studied with the device shown in Figure 6 (8). The device is composed of two bulbs linked by a narrow tube closed on both ends by sintered plates to prevent diffusion of solutions from one bulb to the other. One bulb contains a 50/50 solution of the hydrocarbon investigated and its radical anion in an ethereal solvent, whereas the other bulb contains a 50/50 solution of the radical anion and its dianion in the same solvent. Two platinum wires inserted in the bulbs act as electrodes, and the connecting tube, forming a liquid junction, is filled with a concentrated solution of a salt that contains the same cation as the solutions of the radical anions and dianions. The whole unit is evacuated and immersed in a Dewar flask containing a liquid kept at constant tern-... 

A h, cylindrical cells 0.1—10 A h and button cells 0.04-1.75 A h. The energy density of sintered plate cells is considerably better than their pocket plate counterparts because the electrodes are closer together, and with the high porosity of the plates there is also more active material per unit volume with a 100 A h cell... 

The small sealed sintered plate Ni-Cd cylindrical and prismatic cell constructions have the favorable characteristics of the pocket/tubular plate constructions with increased energy density. The electrodes are thin and the cells have low internal resistance with excellent high rate and low temperature performance. The stem is rugged and can withstand physical and electrical abuse. It requires minimal maintenance. 

The sintered nickel substrate for the cathode is similar to that used for Ni-Cd and Ni-MH cell constructions. The nickel active materials are loaded into the sinter plate using either an aqueous (Bellcore) or alcoholic-based (Air Force or Pickett) electrochemical impregnation process. A 5-10% cobalt additive is deposited with nickel hydroxide to improve charge acceptance. These electrodes have a significantly longer cycle life over the standard vacuum impregnated or pasted nickel electrodes used in commercial Ni-Cd cells. 

A variety of plate formulations are used in vented, sintered nickel-cadmium cells produced by different manufacturers. The plates differ according to the nature of the substrate, method of sintering, impregnation process, formation and termination techniques. The predominate plate fabrication process used for vented sintered plate over the years has been described by Heischer." There are several reviews on electrode fabrication processes that have been used in flooded vented cells. ... 

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