Electrolysis: processes – compositions used therein – and methods – Electrolytic coating – Coating moving substrate
Patent
1995-11-16
1997-04-22
Gorgos, Kathryn L.
Electrolysis: processes, compositions used therein, and methods
Electrolytic coating
Coating moving substrate
296235, 295272, 29DIG11, 29DIG12, 72 47, 205222, 205261, H01M 600, C25D 548, B21C 2326
Patent
active
056226128
DESCRIPTION:
BRIEF SUMMARY
The invention relates to alkaline electrochemical cells and a method of preparing indium plated current collectors for such cells.
Alkaline electrochemical cells are used to power a variety of devices such as flashlights, radios, and other electronic devices. These cells contain a zinc anode, an alkaline electrolyte, a manganese dioxide (MnO.sub.2) cathode, and an electrolyte permeable separator film, typically of cellulose. The anode contacts the negative terminal and the MnO.sub.2 cathode contacts the positive terminal. In the past the zinc anode has been amalgamated with mercury. It is desired to produce alkaline cells with reduced mercury for example "substantially mercury-free" or "zero-added" mercury cells, for environmental concerns. ("Substantially mercury-free" cells are herein defined as containing less than about 50 parts mercury per million parts total cell weight and "zero-added" mercury cells are defined as cells containing no added amounts of mercury, commonly resulting in less than about 10 parts mercury per million parts total cell weight.) In practice it has been difficult to find environmentally compatible substitutes for mercury.
A metal current collector in the shape of a wire or nail is inserted into the anode material and conducts electric current evenly from the zinc to the anode terminal. The current collector is typically made of brass or copper but may also be composed of cadmium, pure zinc or other metals. A current collector nail is typically made by cold-forming brass or copper wire to the desired shape and then cutting the wire to the desired length. It is known to coat the nail with other metals, for example, lead, indium, cadmium and gallium. The coated nail reduces the amount of gassing which may occur in the cell, especially in "substantially mercury-free" or "zero-added" mercury cells. Indium is an attractive coating material for the collectors because it is less of an environmental hazard than lead, cadmium, gallium and mercury.
The invention will be better understood with reference to the drawings in which:
FIG. 1 is a schematic flow diagram depicting the process steps of the invention.
In the process of the present invention, brass, copper or other conventional current collector wire is electroplated with indium before the wire is cold-formed and cut into individual current collectors, typically in the shape of a nail. The indium plated wire is then cold-formed to form a head portion for each current collector by using a punch and die, followed by cutting the wire to form individual collectors. After plating the wire, but prior to cold-forming and cutting it into individual current collectors, the wire is drawn-down to the desired collector diameter. The final collector diameter may vary depending on the size of the cell. The draw-down may typically be to a diameter which is between about 85 and 95 percent of the diameter of the plated wire before drawing. Surprisingly, although the wire has been plated with indium before draw-down, the drawing does not impair the degree of surface smoothness or continuity of the indium plate thereon. In fact the draw-down increases uniformity in the plated surface and enhances its smoothness and luster. The draw-down also increases the adhesion of the plating to the wire. These enhanced properties are believed to increase the effectiveness of the plated current collectors in reducing cell gassing and in reducing load voltage instability during cell discharge.
In the process of the invention, wire 10 (FIG. 1) is passed to a cleaning step 1 primarily to remove grease and oil deposits from its surface. The wire is typically of brass, in its unburnished state, and may typically have a diameter between about 1.3 and 1.9 mm. Electrolytic (cathodic) cleaning is preferred wherein the wire is the cathode (negative electrode) and stainless steel may be the anode (positive electrode). The electrolyte may be an aqueous solution of sodium hydroxide or other commercially available alkaline cleaner. The wire may be subjected to cathodic cleaning by
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Adamson David V.
Barton Paul
Gustar Robert E.
Mihara David R.
Rose Stephen J.
Allen Rose M.
Duracell Inc.
Feltovic Robert J.
Gorgos Kathryn L.
Josephs Barry D.
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