Chemistry: electrical current producing apparatus – product – and – Current producing cell – elements – subcombinations and... – Electrode
Reexamination Certificate
1999-09-30
2001-12-25
Kalafut, Stephen (Department: 1745)
Chemistry: electrical current producing apparatus, product, and
Current producing cell, elements, subcombinations and...
Electrode
C429S212000, C429S230000, C029S623500
Reexamination Certificate
active
06333127
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention generally relates to aqueous electrochemical cells and, more particularly, to an alkaline electrochemical cell having a gel-type electrode.
Conventional alkaline electrochemical cells generally include a cylindrical steel can having a positive electrode, commonly referred to as the cathode, which often comprises manganese dioxide as the active material. The electrochemical cell also includes a negative electrode, commonly referred to as the anode, which often comprises zinc powder as the active material. In conventional bobbin-type cell constructions, the anode is centrally located in a cavity within a tubularly shaped cathode. A cup-shaped separator is located between the anode and the cathode, and an alkaline electrolyte solution simultaneously contacts the anode, the cathode, and the separator. A conductive current collector is typically inserted into the anode active material, and a seal assembly, which commonly includes an annular polymeric seal, such as nylon, provides closure to the open end of the steel can to seal the active electrochemical materials in the can.
Some conventional alkaline cells commonly use a gelled anode which contains carboxymethyl cellulose (CMC), cross-linking type branched polyacrylic acid or a sodium salt thereof, natural gum, or the like as a gelling agent. Examples of conventional gelled anodes are disclosed in U.S. Pat. Nos. 5,587,254 and 4,963,447. The gelled anode is typically formed by uniformly dispersing irregularly shaped zinc powder in a gelled electrolyte containing a gelling agent, such as CMC, and an alkaline electrolyte solution, such as potassium hydroxide. The zinc powder is uniformly suspended in place by the gelling agent. The conventional gelled anode is generally preformed and injected in a gelled state into the cup-shaped separator with an injector. The gelled anode mix typically has a low viscosity and uniform concentration of zinc powder dispersed throughout the anode mix.
Zinc powder is commercially available in various particle shapes and sizes. Conventional zinc powders employed in alkaline batteries are generally characterized as irregularly shaped particles, ranging from lumps or distorted spheroids to elongated tuberous forms. These zinc particles typically have craggy or minor protrusions, and irregular surface characteristics. In conventional cells, the zinc powder is generally suspended in the gelling agent without respect to its orientation. The irregular shaped particles and non-uniform orientation of zinc particles may reduce ion permeation and water flow within the anode and may create void volume, thereby reducing available cell performance. The anode must include a minimal amount of zinc powder to provide sufficient particle-to-particle and particle-to-collector contact, yet not unnecessarily waste excessive zinc beyond the anode's reaction product capacity. Electrochemical cells have generally required a minimum of 28 percent volume of conventional zinc powder in the anode to provide sufficient electronic conductivity.
It is desirable to provide a zinc anode current carrying matrix that maintains good conductivity, high current discharge efficiency and allows for enhanced flow, high volume percent zinc concentrations, and improved packing efficiency.
SUMMARY OF THE INVENTION
The present invention improves the ion permeability of electrolyte in an electrochemical cell. To achieve this and other advantages, and in accordance with the purpose of the invention as embodied and described herein, the present invention provides for an electrochemical cell and process of assembling an electrochemical cell. The electrochemical cell comprises first and second electrodes disposed in a container. The second electrode includes an electrochemically active material including a plurality of flakes coated on at least one surface with an absorbent gelling agent. An electrolyte is disposed in the container and at least some of the electrolyte is absorbed by the absorbent gelling agent.
According to another aspect of the present invention, a process is provided for assembling an electrochemical cell. The process includes the steps of disposing a first electrode in a container, disposing a separator in the container and against a surface of the first electrode. The process also includes the steps of providing a plurality of electrochemically active flakes, preferably zinc flakes, coating an absorbent gelling agent on at least one surface of the flakes, disposing the coated flakes in the container, and orienting the flakes so that the flakes are substantially perpendicular to side walls of the separator. The process further includes the step of disposing electrolyte solution in the separator so that the gelling agent absorbs at least some of the electrolyte solution. Accordingly, a gel-type electrode may be formed within the container, and ion permeation and water flow are enhanced by the orientation of the electrochemically active flakes.
These and other features, advantages and objects of the present invention will be further understood and appreciated by those skilled in the art by reference to the following specification, claims and appended drawings.
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Eveready Battery Company Inc.
Fraser Stewart A.
Kalafut Stephen
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