Chemistry: electrical current producing apparatus – product – and – Current producing cell – elements – subcombinations and... – Electrode
Reexamination Certificate
1998-05-01
2001-08-28
Chaney, Carol (Department: 1745)
Chemistry: electrical current producing apparatus, product, and
Current producing cell, elements, subcombinations and...
Electrode
C429S229000, C029S623100
Reexamination Certificate
active
06280877
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to a method for producing improved anodes containing electrolyte-absorbed polymer particles, such as zinc powder-gel anodes, and to galvanic cells employing such anodes.
BACKGROUND OF THE INVENTION
A conventional type of alkaline cell employs a cathode comprising predominantly an oxidic depolarizer such as manganese dioxide usually admixed with a binder and conductive material such as graphite. The anode usually comprises a consumable anodic material such as powder zinc admixed with a gelling agent such as carboxymethyl cellulose, and a suitable alkaline electrolyte such as an aqueous potassium hydroxide solution, and if desired, mercury. Mercury can raise the hydrogen over-potential of the negative electrode zinc surface thereby suppressing the corrosion of the zinc and suppressing the hydrogen gas generation that usually accompanies the corrosion. However, since mercury is harmful to the environment, attempts have been successfully made to eliminate it from batteries. In addition, with the elimination of mercury in the zinc anode, cell stability suffered due to decreased particle-to-particle contact between zinc particles and decreased contact between the zinc particles and the current collector. Also, the occurrence of strong shock to the cell can cause loss of electrical continuity within the anode.
The use of carboxmethyl cellulose, or its derivatives as the binder and gelling agent for anode construction has been satisfactory from a practical commercial standpoint. Unfortunately, however, when conventional alkaline cells generate gas during abuse charge, post discharge and prolong shelf storage, the gas is often entrapped in the anode. This entrapped gas can cause the anode to swell and the internal cell pressure to rise. If no means for gas release are provided, the cell could rupture and thereby present a hazard.
U.S. Pat. No. 3,884,721 discloses an improved composite anode for use in an alkaline-galvanic cell comprising in combination, zinc particles, an alkaline electrolyte and a cross-linked polyacrylamide to form electrolyte nuggets wherein said zinc particles are distributed throughout said composite anode in a manner such that said zinc particles are in contacting relation with said electrolyte nuggets and with each other.
U.S. Pat. No. 5,376,480 discloses a gel form negative electrode of an alkaline battery that is produced without mercury and enabled uniform dispersion of zinc or zinc alloy powder and an effective metal which can be one or more of an oxide or hydroxide of indium, lead, gallium, or bismuth. The zinc or zinc alloy powder and the effective metal are dry mixed in advance of mixing with a gel form alkaline electrolyte. In order to obtain satisfactorily high vibration strength and impact resistance, fiber material can be added to the gel form negative electrode. The fiber material may be selected among rayon, vinylon, acryl, vinyon, polyamide, polypropylene, polyethylene, mercerized pulp, and linter pulp.
U.S. Pat. No. 4,963,447 discloses an alkaline cell having a gelled zinc negative electrode solely or mainly using, as a gelling agent to hold a zinc powder in an alkaline electrolyte, a granular cross-linking type branched polyacrylic acid, polymethacrylic acid or salts thereof. This gelling agent, holding an alkaline electrolyte, swells and properly maintains the thickness of the electrolyte, whereby the electrolyte can be sufficiently fed to a cell reaction portion and the alkaline cell is imparted with excellent drop resistance and shelf stability.
U.S. Pat. No. 5,587,254 discloses a gel type negative electrode comprising a zinc alloy powder, a gelling agent and an alkaline electrolyte which can be improved by using the following three gelling agents in combination in the gel type negative electrode, namely, a cross-linked polyacrylate type water-absorbing polymer having a dispersion viscosity at 25° C. of at least 15,000 cps as a 0.5 wt % aqueous solution and having a particle size of mainly 100-900 microns, a cross-linked and branched type polyacrylic acid or a salt thereof having a dispersion viscosity at 25° C. of at least 15,000 cps as a 0.5 wt % aqueous solution and having a particle size of mainly 100 microns or smaller, and a granular cross-linked and branched type polyacrylic acid or a salt thereof having a dispersion viscosity at 25° C. of at least 15,000 cps as 0.5 wt % aqueous solution and having a particle size of mainly 100-900 microns.
It is an object of the present invention to provide a method for producing an improved gel negative electrode that when used in a galvanic cell will improve the contact between the zinc particles and the contact between the zinc particles and the current collector and will also improve the shock resistance to provide better cell performance especially during pulse discharge under high drains.
It is another object of the present invention to provide a gel-anode using cross-linked polymer absorbed electrolyte particles that are at least 1,000 microns in length, width or height and are distributed throughout the gel-anode.
The foregoing and additional objects will become more fully apparent from the following description.
SUMMARY OF THE INVENTION
The invention broadly relates to a method for producing an electrode for use in a galvanic cell comprising the steps of:
(a) selecting dehydrated liquid absorbing cross-linked polymer particles which are sized to flow through a 20 Tyler mesh screen and be retained on a 200 Tyler mesh screen; and
b) mixing at least one electrochemically active material, an electrolyte solution, and the selected liquid absorbing cross-linked polymer particles of step (a), wherein, after absorbing the electrolyte, at least 50% of the liquid absorbing cross-linked polymer particles are at least 1000 microns in length, width or height and are substantially distributed throughout the anode.
In step (b) the cross-linked polymer particles could be contacted with electrolyte prior to the particles being mixed in with electrochemically active material and electrolyte in step (b). Preferably, the liquid absorbing cross-linked polymer particles should be gently mixed into the active material and electrolyte so that the particles can absorb the electrolyte to produce electrolyte-absorbed polymer particles that are at least 1,000 microns in length, width or height. Such particles may be irregularly shaped.
The preferred method for preparing the polymer particles is to gently mix the polymer particles into water, preferably deionized water, making sure that the polymer particles do not form an agglomerate. The mixture, in a gel consistency, is dispensed on a surface where the water absorbed polymer particles are placed in an environment to permit the water to evaporate. Preferably, the water absorbed polymer particles could be placed in a heated vented oven, between 50° C. and 100° C., for a time period sufficient to evaporate the water. The dehydrated polymer particles are first ground and then sorted by passing through a 20 Tyler mesh screen and then selecting those that are retained on a 200 Tyler mesh screen. Preferably, the dehydrated polymer could be sorted by passing through a 20 Tyler mesh screen and selecting those that are retained on a 60 Tyler mesh screen. Most preferably, the dehydrated polymer particles could be sorted by passing through a 40 Tyler mesh screen and selecting those that are retained on a 60 Tyler mesh screen.
Preferably, the dehydrated polymer particles should be gently folded into (gently added to) the active material and electrolyte to insure that at least 75% of the dehydrated polymer particles will absorb the electrolyte and produce electrolyte-absorbed polymer particles that are at least about 1,000 microns in length, width or height. The size of the electrolyte-absorbed polymer particles can vary between about 1,000 microns to about 8,000 microns, preferably between about 2,000 microns to about 6,000 microns and most preferably about 5,000 microns
In the preferred embodiment of producing a gelled anode for alkali
Chaney Carol
Eveready Battery Company Inc.
Fraser Stewart A.
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