ELEKTRISCHER AKKUMULATOR

1350725 Electric battery CONSIGLIO NAZIONALE DELLE RICERCHE 4 May 1972 [31 Aug 1971] 20779/72 Heading HlB An electric battery includes a plurality of cells arranged in series, each cell comprising a bipolar electrode serving to separate neighbouring cells and an aqueous electrolyte of zinc bromide which is continuously circulated through the cells during the charging and discharging processes and stored in an autonomous tank when the battery is not in use; the bipolar electrode having deposited on one side a zinc anode and on the other a bromine cathode including an active cathodic mass, the mass containing an active cathodic substance which is insoluble in water and is capable of combining with cathodic bromine to form solid addition products, the substance being selected from alkylammonium perchlorates, diamine bromides or perchlorates, triamine bromides or perchlorates, additive substances being dissolved in the electrolyte to reduce the solubility of the active cathodic substance, to increase the conductivity and the acidity of the electrolyte and to encourage the zinc to deposit in a thin uniform layer. The bipolar electrode in one embodiment, Fig. 3, comprises a metal sheet 6 having a zinc layer 4 on one side and on the other side a plurality of graphite sticks 7 glued by graphite cement 2, with the channels 8 filled with a mixture of graphite, active cathodic substance and powdered porous carbon, surrounded by a retaining ring 5, and closed off by a porous insulating sheet 9. In another embodiment, (Fig. 2, not shown) the zinc layer 4 is located directly on an impermeable sheet of graphite fibres (1) and the sticks and the filling mixture are replaced by a graphite felt (3) impregnated with the active cathodic substance by an exchange process. Alternatively an impermeable moulded graphite sheet (4, Fig. 1, not shown) may be used in place of sheet 6 and have the filling mixture located between ribs moulded into the sheet. The electrolyte preferably comprises an aqueous solution of zinc bromide, hydrobromic acid, sodium sulphate and sodium perchlorate. The sulphate serves to maintain the conductivity of the electrolyte and to prevent free bromine dissolving in water. The perchlorate also serves to maintain conductivity and to reduce solubility of the solid addition products. The active cathodic substance may be tetra methyl, ethyl or butyl ammonium perchlorate, phenyl or cetyl trimethylammonium perchlorate and/or bromide or penta, hexa or deca-methoni