IMPROVEMENTS IN AND RELATING TO ELECTRIC SECONDARY CELLS

1,262,008. Lead cells. MATSUSHITA ELECTRIC INDUSTRIAL CO. Ltd. 30 May, 1969 [30 May, 1968; 15 July, 1968 (2); 17 July, 1968; 18 July, 1968; 14 Nov., 1968], No. 27471/69. Heading H1B. [Also in Divisions C6-C7] Electrodes for a lead secondary cell are formed by rolling a lead-silver alloy to form a thin plate, e.g. 0À1-0À5 mm. thick, electrolytically etching and anodizing to produce a lead oxide layer thereon and then electrolytically reducing the lead oxide in dilute sulphuric acid to metal (see Divisions C6-C7). As shown in Fig. 13, the cell comprises a cylindrical container 20 of polystyrene with a series of radial webs 21 at its closed lower end and a rolled electrode assembly 22. The positive electrode 23 and negative electrode 24 are wound together (Fig. 15) with a spacer 25 and separator 26 between them. The separator may be formed by coating on to a non-woven fabric of polyvinyl chloride a mixture of finely divided diatomaceous earth in an emulsion of vinyl chloridevinyl acetate copolymer in acetone. The spacer is a lattice of polyethylene wires heat bonded at the cross-over points. The cell is provided with upper sealing member 27 of polystyrene and closure member 31, an outer metallic case 28. Positive lead 33 extends through member 27 to terminal 32 and negative lead 34 extends through member 27 to terminal plate 29 which is insulated by ring 30 from casing 28. A catalyst body 36, for causing combination of hydrogen formed during charging of the cell, with oxygen, is provided beneath the sealing member 27. The catalyst is a pressure moulded body of polyethylene tetrafluoride and graphite coated with palladium. The body 36 is surmounted by a moulded disc 37 of graphite and polyethylene tetrafluoride and a disc 38 of polystyrene film through which oxygen is supplied from the outside. A further disc 39 formed by coating and drying a mixture of litharge, glycerine and water, absorbs any electrolyte which might leak from the cell. The electrolyte may be a silica gel containing sulphuric acid, and sodium lignin sulphonate in amount of 0À5-1 g./l. may be added to prevent coarse crystal growth on the electrodes.