PROCESS FOR MANUFACTURING AN ELECTROCHEMICAL CATHODE WITH BUS BAR AND PRODUCTS PRODUCED THEREBY

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a process for manufacturing electrodes and electrodes produced thereby/ and more particularly to a process for manufacturing electrochemical cathodes for use in electrochemical cells and electrochemical cathodes produced thereby.

2. Description of the Prior Art

Metal/air batteries produce electricity by electrochemically coupling in a cell a reactive metallic anode to an air cathode through a suitable electrolyte. As is well known in the art, an air cathode is a typically sheet-like member having opposite surfaces respectively exposed to the atmosphere and to an aqueous electrolyte of the cell/ in which (during cell operation) atmospheric oxygen dissociates while metal of the anode oxidizes providing a usable electric current flow through external circuitry connected between the anode and cathode. The air cathode must be permeable to ait , but substantially hydrophobic (so that aqueous electrolyte will not seep or leak through it)/ and must incorporate an electrically-conductive element for external circuitry.

In present-day commercial practice/ the air cathode is commonly constituted of active carbon (with or without cin added dissociation-promoting catalyst) containing a finely divided hydrophobic polymeric material and incorporating a metal screen as the

conductive element. A variety of anode metals are used including iron/ zinc/ magnesium/ aluminum/ alloys of aluminum etc. Alloys of aluminum and magnesium are considered especially advantageous for particular applications owing to low cost/ lightweight and ability to function as anodes in metal/air batteries using neutral electrolytes/ such as sea water or other aqueous saline solutions. Metal/air batteries have an essentially infinite shelf-storage life rendering them very suitable for standby or emergency uses in that the metal-air battery may be activated by immersing the electrode in an electrolyte.

In U.S. Patent No. 4,906/535, assigned to the same assignee as the present invention/ there is disclosed a process for producing an electrochemical cathode for an electrochemical cell comprised of a current collecting layer or substrate laminated between layers of a nonwoven conductive fibrous web/ preferably of conductive carbon fibers/ impregnated with a mixture of carbon particles and a nonfibrous polymeric substance/ and optionally with a hydrophobic microporous film or layer disposed on one of the layers of the nonwoven conductive fibrous web as well as the product produced thereby.

In the manufacture of metal-air and fuel cells/ as well as "book-cover cathodes" for telecommunications reserve cells (TCR)/ bus bar cables are attached to the air cathode formed in accordance with the process of the aforementioned U.S. Letters Patent. Attachment of such bus bar cable involves the mechanical removal of areas of the carbon and teflon layers to expose the current collecting substrate, e.g., nickel grid for bus bar attachment thereto. The bus bar cable to be soldered to the current collecting substrate requires the application or coating of a thin film of tin-lead alloy on the bus bar, generally

copper braid as well as the use of tin-lead solder in the soldering process.

Such bus bar attachment protocol is inefficient/ time-consuming/ labor intensive/ involves the use of hazardous substance/ i . e . , lead and concomitant hazardous waste disposal problems and is not readily adaptable for automation and cost reductions attendant therewith. OBJECTS OF THE PRESENT INVENTION

An object of the present invention is to provide an improved process for attaching bus bars to an air cathode.

Another object of the present invention is to provide an improved process for attaching bus bars to an air cathode permitting of efficient and effective attachment.

Still another object of the present invention is to provide an improved process for attaching bus bars to an air cathode eliminating the use of hazardous material.

Yet another object of the present invention is to provide an improved process for attaching bus bars to an air cathode readily adaptable to automatic processing.

A further object of the present invention is an improved bus bar/air cathode assembly of improved electrical characteristics.

A still further object of the present invention is an improved bus bar/air cathode assembly of more reproducible electric characteristics. SUMMARY OF THE INVENTION

These and other objects of the present invention are achieved in a process for forming a cathode assembly including positioning bus bar components on one or either side of an air cathode laminate and mechanically fastening together such components.

BRIEF DESCRIPTION OF THE DRAWINGS

Other features and advantages of the present invention will become more readily apparent from the following detailed description when taken with the accompanying drawings wherein:

Figure 1 is a schematic elevational view of an electrochemical cathode of the present invention; and

Figure 2 is a schematic cross-sectional view of the embodiment of the electrochemical cathode of Figure 1;

Figure 3 is an exaggerated partial cross-sectional view of another embodiment of present invention;

Figure 4 is a cross-sectional view of the resulting assembly of the process of Figures 3; and

Figure 5 is a cross-sectional view of a resulting assembly of the process of Figure 3 utilizing a clenching member. DETAILED DESCRIPTION OF THE INVENTION

Referring now to the drawing/ there is illustrated an air cathode/ generally indicated as 10/ a laminate structure comprised of a metal mesh substrate 12/ reactive layers 14 laminated to the mesh substrate 12 and a hydrophobic microporous layer 16 mounted to an outer reactive layer 14. The metal mesh 12 is the current collector of the air cathode 10/ and is formed of a suitable metallic material/ such as nickel/ stainless steel and the like/ formed for example by expanded metal techniques such as disclosed in the aforementioned U.S. Letters Patent No.

Proximate the center line and on either side of the air cathode 10/ there is positioned a suitable bus bar foil or strip 18/ extending the length of the outer reactive layer 14 and hydrophobic microporous layer 16/ and forming an upper end tab member 20

Suitable bus bar material includes foils or strips formed from copper, silver/ nickel/ steel/ aluminum/ brass and like conductive metals.

A riveting gun _; generally indicated as 22/ is positioned on the bus bar foil or strips and is comprised of a riveting head member 24 and a base member 26 for inserting a rivet 28 including cap portion 30 through a strip 18, thence through the air cathode 10 and finally/ through the other strip to form a flattened end portion 32 which cooperates with the cap 30 and thereby capture the air cathode 10 therebetween with the rivet 28 forming a mechanically strong/ low resistance contact with the current collecting substrate 12 of the air cathode 10. The riveting protocol is continued to provide a rivet density of from about 1 to 10 per square inch of the copper foil strips. It will be understood by one of ordinary skill in the art that a riveted air cathod assembly may be formed with one copper foil riveted to one side of an air cathode.

Another embodiment of the present invention is illustrated by Figure 3 with a like composite of an air cathode 10 and copper foils or strips 18 as discussed with reference to Figures 1 and 2 and utilizes a clenching assembly comprised of a clenching hammer 40 and a plate member 42 including a clenching cavity. The clenching hammer 40 is caused to be driven or forced through the composite and into the clenching chamber 44 to effect mechanical fastening or a cinch at 46 similar to riveting whereby carbon and hydrophobic layers tear locally and establish mechanical and electrical contact with the current collecting grid and copper foils. Clenching may be effected at like density/ i .e . , of from about 1 to about 10 per square inch. Likewise/ only one (1) copper foil or strip 18 may be used in the composite

prior to clenching of the composite. Additionally, a clenching member 48/ referring to Figure 5/ may be positioned on the clenching hammer 40 prior to penetration of the composite

TCR cells utilizing riveted copper bus bars of the present invention achieve like reproducibility of TCR cells produced by the tedious labor intensive procedure hereinabove disclosed.

While the present invention has been described with reference to the coupling of a strip of bus bar material for an air cathode of a specific layered configuration/ it will be understood by one of ordinary skill in the art that other cathode structures including reactive layers of other materials including MnO_/ AgO, CaCl./ and the like laminated to a current-collecting layer or grid/ may be processed in accordance with the present invention.