Patent GB-1394753-A (GB)
Title: Electrochemical cell
IPC: H01M12/08
Filed: 1972-07-19
Abstract: 1394753 Rechargeable metal-air battery SOC GENERALE DE CONSTRUCTIONS ELECTRIQUES ET MECANIQUES (ALSTHOM) 19 July 1972 [20 July 1971] 33859/72 Heading H1B A rechargeable liquid electrolyte electrochemical cell having zinc negative electrodes and non-porous positive electrodes which are fed on the same face by a gas containing oxygen and by the electrolyte, comprises (a) a stack of a plurality of groups of components each constituted by a rectangular active region mounted in a frame having apertures therein permitting supply and evacuation of electrolyte and gas, each group having a total thickness less than 1 mm. and comprising (i) a fluid-tight bipolar electrode 1 having on one side 3 a conductive surface with a catalytic coating 5 and on the other side a zinc layer 6 and (ii) a microporous membrane or diaphragm 20, and wherein microducts 9-12 are formed in the electrode frame 2 to facilitate fluid supply and evacuation between the apertures 7, 8 and the active surfaces thereof and the apertures 7, 8 are on opposite edges thereof with an even number on each edge such that alternate apertures are used respectively for opposite electrode face fluid supply or evacuation to give parallel fluid flows in the same direction, and a constant spacing is maintained between the components whose total peripheral portion thickness is equal to that of the central portions thereof, (b) a securing arrangement for maintaining the components assembled, (c) at least one device for selective precipitation and filtration of the zinc oxide entrained by the electrolyte, and (d) an arrangement for circulating the electrolyte. To space the components and permit free fluid circulation with uniform charge loss density the electrode is formed by a 50 micron thick embossed or corugated sheet 4 of stainless steel or conductive plastics material with a 100 micron thick zinc deposit 6 formed on one face and a carbon catalyst coating 5 bonded by PTFE to the other face. The face 3 of the electrode 1 contacts the microporous diaphragm 20; however the opposite face is spaced from diaphragm 20 by an insulating, e.g. polyamide, gauze or cloth 24. Like the other components the gauze 24 is mounted in a plastics insulating frame appropriately apertured to permit fluid transfer. The micro-ducts 9-12 formed by imprinting into the electrode frame may be a few tenths of a millimetre wide and deep and uniformly spaced every 5 mm. and they may diverge from the apertures towards the electrode edge to give uniform distribution of electrolyte flow. The passivation of the zinc layer and the formation of zinc dendrites are reduced by the small spacing between the zinc layer and the microporous diaphragm since the electrolyte flow therethrough is extremely active. Ties or resin over-moulding may facilitate the assembling of the components. The positive electrode may be supplied with a gas emulsion containing air in an alkaline liquid electrolyte, preferably of the same nature as that circulating in contact with the zinc, e.g. KOH. Alternative fluid circulating systems are illustrated in Figs. 3, 4 (not shown), incorporating a pump (34) and a selective precipitation and filtration device (35).