Chemistry: electrical current producing apparatus – product – and – Current producing cell – elements – subcombinations and... – Electrode
Reexamination Certificate
2001-06-13
2004-10-05
Barr, Michael (Department: 1746)
Chemistry: electrical current producing apparatus, product, and
Current producing cell, elements, subcombinations and...
Electrode
C429S236000, C429S238000, C429S241000, C429S242000
Reexamination Certificate
active
06800398
ABSTRACT:
Technical Field of the Invention
The present invention relates to electrodes for alkaline storage batteries, a method for manufacturing electrodes for alkaline storage batteries, and improvement of alkaline storage batteries.
Background of the Technology
Alkaline storage batteries as represented by nickel-hydrogen batteries and nickel-cadmium batteries, etc., are small, light weight and provides high output densities. In recent years, their field of practical applications is not limited to small devices such as personal computers and mobile phones but is extending to the area of large size power sources such as for electric vehicles and hybrid electric vehicles. In association with the expanding applications of these batteries, increasingly higher capacity and reliability are now being required.
In alkaline storage batteries, a prismatic structure in which a battery is configured by assembling plate-form positive electrodes and negative electrodes with separators interposed and housing in a prismatic container, and a cylindrical structure in which a battery is configured by spirally winding a rectangular positive electrode and a negative electrode with a separator interposed thus configuring an electrode group and housing it in a cylindrical container, are generally adopted.
On the other hand, in recent years, three-dimensional porous metal substrates (hereinafter porous substrates) such as foam metal of nickel or non-woven metal fabric having three-dimensionally connected space with as high a porosity as exceeding 90% have been developed, and a new method for manufacturing electrodes by directly filling paste of active material particles into these substrates has been developed, and these electrodes are now in wide use in the above-mentioned prismatic and cylindrical batteries as the electrodes suited for higher capacity. However, it has become clear that there exist reliability related issues arising from the manufacturing method and structure of the electrodes employing the above-mentioned three-dimensional porous substrate. It is an object of the present invention to improve the electrodes from the standpoint of the structure and the manufacturing method, and to establish reliability of alkaline storage batteries provided with electrodes that employ the above-mentioned three-dimensional porous substrate.
As an active material paste to be filled into a porous substrate, active material paste for the positive electrode of an alkaline storage battery that contains nickel hydroxide as the main constituent added with a material required for electrode reaction such as cobalt metal, nickel metal, and carbon powder, and active material paste for the negative electrode that contains hydrogen absorbing alloy or cadmium hydroxide as the main constituent added with a material such as carbon powder and nickel powder required for electrode reaction, and a binder such as carboxymethyl cellulose and the like are in use.
Electrodes using three-dimensional porous bodies filled with the above-mentioned active materials have been generally used as a positive electrode or a negative electrode of a battery after being pressed into a predetermined thickness after the paste was filled.
It is common that a dense surface layer has been formed on the surface of an electrode pressed as above. Such a dense surface layer hampers penetration of liquid electrolyte into the inside causing dispersion in the quantity of injected liquid electrolyte from battery to battery thus suffering from dispersion in the characteristics.
On the other hand, the above-mentioned three-dimensional porous body is a structural material with an originally low degree of freedom of deformation against bending force. When an electrode fabricated by filling an active material into such a structural material and further pressing the degree of freedom against bending force is further limited. When trying to configure an electrode group by forcefully winding the electrode, disorderly cracks, may occur on the outside of the electrode being wound, or a squarishly wound electrode group with poor roundness is formed, thereby causing failure when inserting into a cylindrical metal container. Furthermore, at the above-mentioned cracks, burrs from the damaged portion may project from the surface or active material particles may flow out from the damaged portion, thus penetrating the separator and causing short-circuits of various sizes, further causing initial or time-varying voltage failures or short-circuit failures.
As a prior art for improving the above issues, a technique has been proposed as disclosed in Japanese Laid-Open Patent Application No. Sho 60-133655, in which V-shaped grooves are formed on both sides of an electrode and winding it with the direction of the grooves in parallel to the axis of winding. Furthermore, in Japanese Laid-Open Patent Application No. Hei 5-41211, disclosure has been made on grooves having a trapezoidal or semi-elliptical cross section instead of grooves having a V-shaped cross section with which a porous metal body is easy to fracture. However, formation of grooves on both sides is disadvantageous in increasing the quantity of active material to be filled.
Accordingly, as a method for manufacturing by uniformly forming grooves by making the distribution of filled active material uniform, one in which active material paste is filled from one side of a three-dimensional porous metal body toward the opposite side has been proposed in Japanese Laid-Open Patent Application No. Hei 9-106814. Also, a technique is disclosed in which a layer filled with a high-density active material is formed on the side of the above-mentioned filled surface by filling the active material in a manner such that it hardly passes to the opposite side, and a layer filled with a low-density active material or a non-filled layer is formed on the opposite side, and grooves are formed on the surface of the low-density filling side. Furthermore, in the same Japanese Laid-Open Patent Application No. Hei 9-106814, a description is made on examples of a method of manufacturing in which grooves or rifts are formed on one side of a three-dimensional porous material body prior to filling paste and a method of manufacturing an electrode in which active material paste is filled from the side opposite to the side on which the grooves or rifts are provided, and further, on a structure in which electrodes are wound in a manner such that the above-mentioned grooves face outward.
On the other hand, in Japanese Laid-Open Patent Application No. Hei 9-27342, an electrode comprising a high-density active material-filled layer and a low-density active material-filled layer similar to the one disclosed in Japanese Laid-Open Patent Application No. Hei 9-106814 is disclosed, and both of a structure made by winding with the low-density active material-filled layer facing inward and a structure made by winding with the layer facing outward are disclosed.
In addition, as an example, a description is made on a method of manufacturing in which grooves or rifts are provided on a three-dimensional porous body prior to the step of filling an active material and active material paste is filled from the side opposite to the side where the grooves or rifts have been provided, and a method of manufacturing in which an active material is filled conversely from the side where the grooves or rifts have been provided.
In either case, electrodes having grooves as described above showed improved flexibility in a configuration in which the electrodes had been wound with the side having grooves facing outward due to freedom of extension of the surface as given by cracks occurring preferentially inside the grooves, and tended to cause fewer voltage failures.
Nevertheless, it has become clear that many voltage failure cases still occur. From the analysis of the causes, it was found that, in the above existing groove forming configuration, burrs of cracks occurring inside the grooves either bulge and project out by the winding force or active material particles from the cracks
Asano Gota
Furuya Satoshi
Inaba Yoshihisa
Miyahisa Masaharu
Shiosaki Ayahito
Barr Michael
RatnerPrestia
Wills Monique
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