Chemistry: electrical current producing apparatus – product – and – Current producing cell – elements – subcombinations and... – Electrode
Reexamination Certificate
2002-08-13
2004-01-27
Dunn, Tom (Department: 1725)
Chemistry: electrical current producing apparatus, product, and
Current producing cell, elements, subcombinations and...
Electrode
C429S233000, C029S002000
Reexamination Certificate
active
06682852
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a method of manufacturing a plate for a battery electrode and the plate for a battery electrode manufactured by the method, and more particularly to the plate for an electrode which is preferably used for a supply battery of an electric car because of a great thickness thereof to increase the amount of an active substance to be applied thereto and because of a preferable contact thereof with the active substance applied thereto to prevent it from dropping therefrom.
BACKGROUND ART
Heretofore, generally, as the plate of an electrode for using a positive electrode and a negative electrode of a nickel/hydrogen battery, a nickel/cadmium battery or the like, principally, a pore-formed nickel-plated steel plate (hereinafter referred to as punching metal) formed by plating an iron plate on which pores are formed by punching is used. An active substance is applied to the punching metal to form the electrode. In the case of a cylindrical battery, the electrode comprising belt-shaped positive and negative electrodes is spirally wound through a separator to accommodate them therein. In the case of a rectangular or square battery, positive and negative electrodes are layered on each other through a separator to accommodate them therein.
The punching metal is used as the plate for a battery electrode by punching a flat cold-rolled steel plate having a thickness of 60 &mgr;m-100 &mgr;m to form thereon circular pores, the diameter of which is 1.0 mm-2.5 mm in a required pattern such that the open area percentage thereof is 40%-50% and then nickel-plating the steel plate to keep it resistant to corrosion.
As the plate of an electrode consisting of positive and negative electrodes of a lithium primary battery, mainly, a lath processed from metal such as SUS and Ti is used. The lath is charged with an active substance to form the electrode. In a lithium secondary battery, the active substance is applied in a required thickness to both surfaces of a metal core material made of an aluminum foil to form a positive electrode, and the active substance is applied in a required thickness to both surfaces of a metal core material made of a copper foil to form a negative electrode.
As the plate of an air electrode to be used as the positive electrode of an air zinc battery, mainly, a metal screen (nickel-plated SUS mesh) is used. As a zinc storage battery which attracts public attention recently as a car battery, a cast lattice or an expanded lattice consisting of lead alloy (Pb/Sb alloy, Pb/Ca alloy, Pb/Ca/Sn alloy or the like) is used. The active substance is applied to the screen and the lattice to form the electrode.
Further, in recent years, as the plate of the electrode of the nickel/hydrogen battery, the nickel/cadmium battery, and the lithium primary battery, porous metal sheets formed by chemically plating resinous foamed materials, nonwoven cloths or mesh materials to make them electrically conductive, and then electroplating them, and then, removing resinous materials and sintering them are also used.
Any of the above-described plates for a battery electrode are flat. An active substance is applied to both surfaces thereof to fill it into pores formed thereon and coat both surfaces thereof with the active substance in a required thickness. Because the above-described punching metal, the lath, and the metal screen are not three-dimensional, they are not in close contact with the active substance and thus have a low active substance-holding force. In particular, if they have large pores formed thereon, the active substance is likely to separate and drop therefrom during the manufacture and use of an electrode. In order to solve the problem, a method of adding a large amount of binder to the active substance to prevent it from separating and dropping from the plate is known. But when a large amount of binder is added to the active substance, the reactivity of the active substance deteriorates, and thus the battery characteristic is inferior.
The active substance is filled into pores of the foamed porous metal sheet having a three-dimensional structure. Thus, the porous metal material has a higher active substance-holding property than the punching metal and the metal screen. But in the foamed porous metal material, the skeleton thereof surrounding the pores is not thick. Thus, the foamed porous metal material has a low electricity-collecting performance, thus being incapable of accomplishing a rapid electric charge or discharge when a rapid electric charge or discharge is required.
Because any of the conventional plates for an electrode is thin, the active substance is thinly applied thereto in the thickness direction thereof. Therefore, the electrode has a low electrical conductivity in its thickness direction. Thus, it is difficult to improve the characteristic of the battery.
In order to solve this problem, in Japanese Laid-Open Patent Publications Nos. 7-130370 and 7-335208, there are proposed electrodes having an apparent thickness twice as great as that of a metal plate or a metal foil, including the thickness of burrs each formed on the periphery of each of pores formed on the metal plate or the metal foil by using upper and lower dies. However, when pores are formed by a pair of dies, the maximum open area percentage is about 50%. Further, it is difficult to form many fine pores on the entire surface of the metal plate or the metal foil by reducing the diameter of each pore and the pitch between the pores. Therefore, even though the burr is formed on the periphery of each pore, the burr has a low occupation percentage and an insufficient active substance-holding force. In addition, because the diameter of each pore is large, the active substance charged into the pores is likely to be dropped therefrom. Further, because the pitch between the pores is long, the area of the metal foil or the metal plate is great, which prevents movement of ions in the active substance. Thus, these electrodes cause batteries to have inferior performance. In order to solve these problems, it is conceivable to reduce the diameter of each pore and the pitch between the pores. But it is technically very difficult and very costly to form the pores by a pair of upper and lower dies as described above. Furthermore, only one metal plate having burrs formed thereon does not allow the application amount of the active substance to be increased so much.
The present invention has been made in view of the above-described problems. It is accordingly an object of the present invention to provide a method of manufacturing a plate for a battery electrode which holds an active substance thereon firmly and allows a large amount of the active substance to be applied thereto in the thickness direction thereof and provide the plate for a battery electrode manufactured by the method.
DISCLOSURE OF THE INVENTION
In order to solve the above-described problem, firstly, there is provided a method of manufacturing a plate for a battery electrode comprising the steps of: passing a thin metal sheet between a pair of embossing rotation rollers having concave portions and convex portions formed on a peripheral surface thereof to form concave portions and convex portions on an entire surface of the metal sheet, and form pores each on an apex of each of the concave portions and convex portions and generate burrs each projecting outward from a peripheral edge of each of the pores by a pressing force during formation of the concave portions and convex portions.
According to the above-described method, by merely passing the metal sheet between a pair of the embossing rotation rollers, comparatively fine concave portions and convex portions can be formed on the entire surface thereof, and at the same time, pores are each formed on the apex of each concave portion and convex portion, and the burr can be projected from the peripheral edge of each pore. Thus, according to the method utilizing the embossing method, compared with the conventional method of forming pores by means of upper and lower dies
Dunn Tom
Katayama Special Industries Ltd.
Pittman Zidia
Sughrue & Mion, PLLC
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