Fibre 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. 

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. 

Recently, cells employing thick sintered nickel plates on nickel-plated porous steel substrates have been developed which have greatly improved energy densities. The active material is introduced by electroprecipitation. Electrodes based on nickel fibre supports are also being studied. 

With the preceding as background, a two-layered AGM separator was evaluated in a further ALABC project [19,20]. This separator consisted of a layer of 100% fine fibres (high surface area) and a second layer made of a mixture of 40% fine fibres with the addition of coarse fibres and chopped structural fibres (low surface area) [21]. Both the positive and negative plates were wrapped by this separator, with the 100% fine-fibre layer facing the electrodes the cell configuration is shown... 

Amperometric electrodes that are extremely thin (<1 pm diameter) are called ultramicroelectrodes and have a number of advantages over conventional electrodes. Being narrower than the diffusion rate thickness, mass transport is enhanced, the signal-to-noise ratio is improved and the measurements can be made in resistive matrices such as nonaqueous solvents. These have huge applications in medicine as they can lit inside a living cell. Carbon fibre electrodes are coated in insulating polymer and plated with a thin layer of metal at the exposed tip to prevent fouling of the carbon itself. These can then be used to measure analytes of interest in various cells and membranes of the human body. 

Yusaza, Japan, have been developing prototype batteries for electric vehicle applications, claiming 200 maintenance-free cycles at 100% depth of diseharge. The more successful, but still unsatisfactory, batteries such as these are based on the use of PTFE bonded pressed plate zinc electrodes and sintered, plastic bonded pressed plate or fibre or expanded foam nickel electrodes to improve conductance. 

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