GB948745A - Improvements in or relating to an electrode for an electric cell or battery - Google Patents

Abstract

<PICT:0948745/C3/1> An electrode for a cell or battery is made by depositing a metal in micro-porous form on a carrier and then densifying the adherent layer by mechanical pressure. The microporous layer, e.g. of Zn, Ag or Cd on a metal sheet support of Cu, Ag or Ni, or galvanized iron, is formed using an electrolyte of low concentration in metal ions, e.g. below 10% by weight of metal, but of high conductivity, at temperatures below 50 DEG C., and at a potential to avoid gassing, e.g. 5V with 10 to 15 cms. between the electrodes. The high conductivity is achieved by adding non-plating salts which may "complex" the metal ion or impart "common ion" properties, e.g. using an alkaline zincate electrolyte, cadmium halide and sodium and ammonium chloride, or alkaline silver cyanide. The over-voltage and viscosity of the electrolyte may be usefully increased by adding polysaccharides, proteins, e.g. gelatin, or soluble polymers, e.g. polyvinyl pyrollidone. In a suitable apparatus, perforated or plain strip of Cu, Ag, or Zn is cleaned and may also be etched, and after masking at the edges where electrodes are to be attached, is then fed from a coil 30 into a plating tank containing electrolyte 32, through which it is led over non-conducting guide rolls R, and between anodes 34 of the metal to be deposited. The electrolyte is circulated through filters 35 with minimum agitation of the liquid. The coated strip then passes through adjustable pressure rollers 37 to compact the coating to the desired density, and is cut to shape at stage 38. Preferably the strips, especially in the case of zinc, are stacked in racks, washed, and fed into an amalgamating tank containing a mercury salt where 0.25-5% by weight of the coating in terms of mercury is absorbed in the coating. The strips are then rinsed, dried, the masking removed, and lead strip terminals are welded on. The degree of compaction at stage 37 increases the density of the porous coating of particle size about 1-8 m , to about 35-65% of the solid metal. The mercury amalgamation step increases the over-potential property of the electrode, and reduces gassing in use. In a modified apparatus, using sheet cut to size, a bi-metallic electrode is made by mounting a sheet of silver centrally in a two-compartment cell, one side containing a cadmium or zinc electrolyte and anode, and the other silver. After compaction the silver coating may be oxidized anodically.