Metal working – Method of mechanical manufacture – Electrical device making
Reexamination Certificate
1998-09-30
2001-02-27
Nuzzolillo, Maria (Department: 1745)
Metal working
Method of mechanical manufacture
Electrical device making
C429S121000, C429S122000, C429S161000, C429S211000
Reexamination Certificate
active
06193765
ABSTRACT:
BACKGROUND OF THE INVENTION
(1) Field of the Invention
This invention relates to a method of manufacturing a cylindrical non-aqueous electrolyte secondary cell, and more particularly to a method of manufacturing a cylindrical non-aqueous electrolyte secondary cell usable for a battery-powered vehicle and the like, wherein a high power density is required.
(2) Description of the Prior Art
A conventional cell of this type generally has a spiral type electrode assembly in which a sheet type positive electrode and negative electrode are spirally wound with a separator disposed therebetween. Electric current is collected from the spiral electrode assembly through conductive labs that are attached on each end part of the aforementioned electrode and current terminals that are electrically connected to the conductive tabs. In a cell of this type, when the cell is a small-sized cylindrical non-aqueous electrolyte secondary cell with a small electric current, the current collecting effect can be sufficient. However, when the cell is a large-sized one with a large electric current, it is difficult to obtain a satisfactory current collecting effect.
In view of the above problem, Japanese Unexamined Patent Publication No. 6-267528 discloses a cylindrical non-aqueous electrolyte secondary cell having the following features. The cell has a sheet type current collector in both the positive electrode and the negative electrode. In both electrodes, a lengthwise end area of the current collector is protruded from a separator, and at the same time the lengthwise end area to which a lead is to be attached is exposed without an active material applied thereon. Then, a positive electrode lead-attaching area and a positive electrode lead, and a negative electrode lead-attaching area and a negative electrode lead are respectively welded.
However, such cylindrical non-aqueous electrolyte secondary cells have certain drawbacks. For the cells of such construction, spot welding is generally employed to weld a lead to a lead-attaching area in each electrode. In this case, when the current collectors have a small thickness of less than 50 &mgr;m, the lead-attaching area thereof is apt to be damaged since, in spot welding, pressure is applied to the area. To prevent the damage, the lead-attaching area requires a reinforcement means, for example, by metal foil and the like, which consequently lowers production efficiency.
As a solution to this problem, laser welding can be employed to weld a lead to a lead-attaching area in each electrode. Laser welding is a non-contact type welding method, in which no pressure is applied on to lead-attaching areas. The reinforcement means to the lead-attaching areas can therefore be eliminated, and workability in manufacturing a cell is thereby improved.
However, laser welding incurs a different problem.
In the present state of the art, in welding a lead to a lead-attaching area, it is extremely difficult to direct a laser beam to an exact position to be welded. Therefore, when a laser beam is applied onto a lead, an area in the electrode assembly except the region to be welded is also exposed to the laser beam indiscriminately. As a result, the irradiated area of the lead is fused and holes are formed, and the laser beam passes through the holes and reaches the internal electrode assembly, resulting in fusion of the electrode assembly and thereby a short circuit.
SUMMARY OF THE INVENTION
In view of the above problems, it is an object of the present invention to provide a method of manufacturing a cylindrical non-aqueous electrolyte secondary cell wherein a laser welding of a lead-attaching area and a lead can be carried out without fear of a short circuit resulting from fusion of the electrode assembly by a laser beam.
It is another object of the present invention to provide a method of manufacturing a cylindrical non-aqueous electrolyte secondary cell having remarkably improved power density by substantially reducing an internal resistance of the cell.
It is further another object of the present invention to provide a method of manufacturing a cylindrical non-aqueous electrolyte secondary cell wherein the production efficiency is improved by eliminating the step of reinforcing lead-attaching areas.
These and other objects are accomplished in accordance with the present invention by employing a method of manufacturing a rechargeable cylindrical non-aqueous electrolyte secondary cell, comprising the steps of:
a first step of forming a lead-attaching area, on which an active material layer is not formed, on at least one current collector in a positive electrode having a positive electrode active material layer formed on both sides of a sheet type positive electrode current collector and a negative electrode having a negative electrode active material layer formed on both sides of a sheet type negative electrode current collector, and winding both the electrodes into a spiral shape with disposing a sheet type separator therebetween so that the lead-attaching area is protruded from an end part of the separator; and
a second step of disposing a lead at an edge of the lead-attaching area with interposing a metal plate having a multiplicity of holes and thereafter laser-welding the lead and the metal plate and the lead-attaching area together by applying a laser beam with a spot diameter larger than a hole diameter of the metal plate.
The reasons for accomplishing the aforementioned objects are as follows. In the laser-welding step described above, a laser beam is applied to the subjected lead. In the subjected lead, even if an area where the lead-attaching area is not disposed is irradiated with the laser beam and holes are formed by the laser irradiation, the internal electrode assembly is not fully irradiated with the laser beam passing through the lead. Therefore, the damage to the electrode assembly such as fusion of the electrode assembly and a consequent short circuit can be avoided. More specifically, the laser beam is completely or partially shielded by the metal plate disposed between the lead and the lead-attaching area because the laser spot diameter is larger than the hole diameter of the metal plate. When the laser beam is completely shielded, the electrode assembly is not irradiated with the beam, and even when the beam is partially shielded, the beam which reaches the electrode assembly is only the portion which passes through the holes of the metal plate. In other words, even if the laser beam penetrates the lead and hits the electrode assembly, the strength of the laser is diminished by the metal plate to the degree that it does not affect the electrode assembly, by the time it reaches the electrode assembly.
In addition, since the lead-attaching area integrally formed with the current collector has a sheet-like shape and the lead-attaching area is attached to a lead by laser welding, a small potential gradient and an even current distribution can be obtained in the current collector. Consequently, even with a large-sized cell, electric current is impartially corrected from the electrodes with a large area, and thereby the internal resistance of the cell is remarkably reduced.
In the method according to the present invention, a rate of hole area of the metal plate may be from 45 to 75%.
The reason for such restriction of the rate of hole area of the metal plate is as follows. If a rate of hole area of the metal plate is rendered smaller, the metal plate with holes will have more similar effect to that of the metal plate without holes, and consequently, the effect of the metal plate with holes will simply become similar to the lead with an increased thickness. When a thickness of the lead is increased, a laser output power should be increased correspondingly in order to properly carry out the laser welding. An increased laser output power will accordingly increase the possibility of the damage to the electrode assembly by a laser beam.
On the other hand, if a rate of hole area of the metal plate is too large, the electrical connection between the lead and the me
Inomata Hideyuki
Nakanishi Naoya
Nishio Koji
Nogami Mitsuzou
Yonezu Ikuo
Armstrong, Westerman Hattori, McLeland & Naughton
Dove Tracy
Nuzzolillo Maria
Sanyo Electric Co,. Ltd.
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