Patent GB-1319492-A (GB)
Title: Rechargeable metal halide battery
IPC: H01M12/08
Filed: 1970-10-08
Abstract: 1319492 Metal halide batteries ZITO CO Inc 8 Oct 1970 [20 Oct 1969] 47928/70 Heading H1B A rechargeable metal halide battery comprises an end cathode 14 connected to terminal screw 15, an end anode 18 connected to terminal screw 20 and an intermediate bipolar electrode 22, all immersed in a liquid electrolyte 23. Cathode 14.-This includes a halogen-entrapment of adsorbent layer 24 having an extended surface 25 in contact with the electrolyte, the other surface of the layer 24 being bonded to a barrier layer 28 which is impermeable to halogen (i.e. chlorine, bromine or iodine) and is also impermeable to the electrolyte. The layer 28 is bonded to a protective layer 34 with a metal screen 32 sandwiched therebetween, this screen being connected to terminal 15. Layer 34 is impermeable to halogen and to the electrolyte. Exposed portions of the layer 28 and screen 32 are coated with an impermeable insulating film 35. Barrier layer 28 conducts electricity between the layer 24 and screen 32 and has a volume resistivity p and thickness d such that pd is equal to or less than 0À1 ohms-in.<SP>2</SP>. Preferably, layer 24 also conducts electricity. The preferred electrolyte is zinc bromide in an aqueous solution and the layer 24 for entrapping bromine consists of activated carbon particles bonded together by a bromine-inert bonding agent. The bonding process bonds the carbon particles together without flowing into the adsorbent pores thereof so that the layer 24 may adsorb at least half its own weight of bromine. Suitable bonding agents are: polytetrafluoroethylene, polyvinylidene fluoride, polymonochlorotrifluoroethylene, fluorinated polyethylene, polyvinyl chloride homopolymers, polyvinylidene chloride homopolymers and copolymers, vinyl chloride copolymers, polymethacrylates, and polyalkylenes. The barrier layer 28 consists of highly electroconductive carbon particles bonded by an agent similar to that used for the layer 24. The protective layer 34 may consist of a film of the bonding agent but preferably it comprises a layer similar to the layer 28, the two layers encasing the metal screen 32 which is preferably of copper. Anode 18.-This comprises a metal screen 38 sandwiched between a barrier layer 40 and protective layer 42, these components being identical to the corresponding components 32, 28, 34 of the cathode. However, the surface 44 of the layer 40 is roughened by sandblasting to provide an electroplating surface for the zinc. The screen 38 is connected to terminal 20. Intermediate electrode 22.-This comprises layers 46, 56 identical to layers 28, 24 of the cathode; however, layer 46 has a roughened surface 48 similar to surface 44 of the anode. Electrolyte.-The preferred zinc bromide in an aqueous solution may be replaced by another liquid medium containing a salt of an electroplatable metal and by the halogen chlorine or iodine. When an aqueous liquid medium is employed, suitable metals are zinc, nickel, cadmium, tin, lead, and copper. In a non- aqueous liquid medium such as may be used for chlorine, reactive metals such as sodium, potassium, and lithium, may also be used. Porous separators 60 having ribs 62 are located between the anodic and cathodic surfaces and retard the tendency for halogen molecules to migrate to the anode. Insulating barriers 70, 72 extend across the top of the case 12. To insure adequate battery output the interface resistance between the electrolyte and each cathode or anode surface is caused to be not greater than 0À05 ohms per square inch of the interface area. During charging, the metal, e.g. zinc, in the electrolyte is plated on the surfaces 44, 48 and the halogen, e.g. bromine, is adsorbed by the layers 24, 56.