Composite current collector
Composite current collectors containing coatings of metals, alloys or compounds, selected from the group of Zn, Cd, Hg, Ga, In, Tl, Sn, Pb, As, Sb, Bi and Se on non-metallic, non-conductive or poorly-conductive substrates are disclosed. The composite current collectors can be used in electrochemical cells particularly sealed cells requiring a long storage life. Selected metals, metal alloys or metal compounds are applied to polymer or ceramic substrates by vacuum deposition techniques, extrusion, conductive paints (dispersed as particles in a suitable paint), electroless deposition, cementation; or after suitable metallization by galvanic means (electrodeposition or electrophoresis). Metal compound coatings are reduced to their respective metals by chemical or galvanic means. The current collectors described are particular suitable for use in sealed primary or rechargeable galvanic cells containing mercury-fee and lead-free alkaline zinc electrodes.
1. An electrochemical cell which is a sealed lead-acid cell or battery comprising a composite current collector having a density in the range of 0.1 to 10 g/cm 3 wherein the voltage drop along the entire height of said composite current collector at an applied current of 100 Amperes ranges from 1 mV to 1 V, said composite current collector comprising a metallic layer on a polymer substrate characterized by:
(i) said metallic layer being (1) an alloy of two or more metals or (2) at least one metal selected from the group of Zn, Cd, Hg, Ga, In, Tl, Sn, Pb, As, Sb, Bi and Se; and
(ii) said metallic layer having a thickness in the range of 1 and 5,000 microns.
2. An electrochemical cell which is a sealed galvanic cell comprising a zinc negative electrode which is substantially free of Hg, Cd and Pb, said zinc negative electrode comprising a composite current collector, said composite current collector being substantially free of Cu and Fe, having a density between 01 and 3 g/cm 3 , wherein the voltage drop across the entire height of said composite current collector at an applied current of 1 Ampere is between 1 mV and 250 mV, said composite current collector comprising a metallic layer on a polymer substrate characterized by:
(i) said metallic layer being selected from the group of In, Sn or In—Sn alloys, and
(ii) said metallic layer having a thickness in the range of 1 and 500 microns.
3. An electrochemical cell according to claim 1 or claim 2 , wherein the polymer substrate surface is rendered conductive by applying a conductive paint containing (1) at least one metal, (2) a metal alloy or (3) at least one compound, selected from the group of Zn, Cd, Hg, Ga, In, Tl, Sn, Pb, As, Sb, Bi and Se.
4. An electrochemical cell according to claim 1 or claim 2 , wherein said metallic coating is built up to its desired thickness by electrodeposition, electroless deposition, electrophoretic deposition, PCD, CVD, sputtering, cold or hot spraying of powders or melts or said metallic coating is attached to the substrate using an adhesive.
5. An electrochemical cell according to claim 1 or claim 2 wherein said metallic layer has a tapered thickness profile.
6. An electrochemical cell according to claim 1 or claim 2 , wherein said composite current collector has the shape of a nail, tube, foil, plate, woven mesh, expanded mesh or more complex shape selected from the group consisting of spiral, blade, formed or bent foil or tube, book mold type grid, radial grid, expanded grid, punched foil, perforated foils and open cell foam.
7. An electrochemical cell comprising a composite current collector according to claim 1 or claim 2 wherein said polymer substrate is selected from the group of filled or unfilled epoxy resin composites; epoxy resins; cellulose based materials; thermoplastic polyolefins (TPOs); thermoplastic polyester resins; thermoplastic polyester elastomers; crystalline, semi-crystalline and amorphous polymers; cellulose based materials; polyethylene; polypropylene; polyvinyl chloride (PVC); polytetrafluoroethylene (PTFE); polystyrene; acrylonitrile-butadiene-styrene (ABS); polyphthalamide (PPA), polycarbonate (PC), polyamide (PA), polyester (PET, PBT), polyacetals (POM); liquid crystal polymers (LCP), polyphenylene sulfide (PPS), polysulfone (PS) and polyetherimide (PEI); and wherein said polymer substrate contains between 0% and 75% per volume and/or weight of one or more filler materials selected from the group of (1) at least one metal, (2) a metal alloy or (3) at least one compound, selected from the group of Zn, Cd, Hg, Ga, In, Tl, Sn, Pb, As, Sb, Bi and Se.
8. An electrochemical cell according to claim 2 wherein said composite current collector is suitably perforated or hollowed to provide space for gas expansion, additional electrolyte, active electrode material or gas recombination device or devices.
9. An electrochemical cell according to claim 2 , which contains a positive electrode comprising at least one active material selected from the group of manganese dioxide, nickel oxides and oxygen.
10. An electrochemical cell according to claim 2 , which is a cylindrical cell.
11. An electrochemical cell according to claim 2 , which after 6 years of storage at room temperature and/or 4 weeks at 65° C. has a pass rate with respect to leakage/frosting of over 85% and has a discharge capacity retention of more than 10%.
12. An electrochemical cell according to claim 2 , wherein the composite current collector limits the short circuit current of the cell when expressed in Amperes to a value between 50% and 100% of the value of the zinc amount expressed in grams.
13. An electrochemical cell according to claim 2 , wherein the composite current collector acts as a fuse and at least a portion of said metallic layer melts at a predetermined current disrupting the current flow in and out of the galvanic cell.
14. An electrochemical cell according to claim 2 , which contains an active electrode material, said active electrode material containing composite conductive particles selected from the group of flakes, needles or platelets, and wherein said composite conductive particles are in electrical contact with said composite current collector.
15. An electrochemical cell comprising a composite current collector having a density in the range of 0.1 to 10 g/cm 3 , said composite current collector comprising a metallic layer on a polymer substrate characterized by:
(i) said metallic layer being (1) an alloy of two or more metals or (2) at least one metal selected from the group of Zn, Cd, Hg, Ga, In, Tl, Sn, Pb, As, Sb, Bi and Se; and
(ii) said metallic layer having a thickness in the range of 1 and 5,000 micron; and
(iii) said polymer substrate being selected from the group of filled or unfilled epoxy resin composites; epoxy resins; cellulose based materials; thermoplastic polyolefins (TPOs); thermoplastic polyester resins; thermoplastic polyester elastomers; crystalline, semi-crystalline and amorphous polymers; cellulose based materials; polyethylene; polypropylene: polyvinyl chloride (PVC); polytetrafluoroethylene (PTFE): polystyrene; acrylonitrile-butadiene-styrene (ABS); polyphthalamide (PPA), polycarbonate (PC), polyamide (PA), polyester (PET, PBT), polyacetals (POM); liquid crystal polymers (LCP), polyphenylene sulfide (PPS), polysulfone (PS) and polyetherimide (PEI); and wherein said polymer substrate contains between 0% and 75% per volume and/or weight of one or more filler materials selected from the group of (1) at least one metal, (2) a metal alloy or (3) at least one compound, selected from the group of Zn, Cd, Hg, Ga, In, Tl, Sn, Pb, As, Sb, Bi and Se; and
(iv) said filler material in said polymer substrate being at least one compound selected from the group of Zn, Cd, Hg, Ga, In, Tl, Sn, Pb, As, Sb, Bi and Se which is subsequently reduced to its metallic form on and near the outer surface of said polymer substrate.