JP2002198102A - Manufacturing method of square-type battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a preparation method of a square-type battery, wherein short circuiting between a positive electrode and a negative electrode of the battery is avoided and a voltage reduction will not be caused during storage of the battery by improving the manufacturing process of the electrode group. SOLUTION: A spiral electrode group 1 is formed by winding a sheet-formed positive electrode, a separator and a sheet-formed negative electrode around a flat bobbin; after the bobbin is pulled out, a thin plate 3 is inserted into a central gap part 2 of the electrode group instead of the bobbin; the thin plate 3 is abutted on the inner peripheral folding part of the electrode group at both ends of the longitudinal direction of the central gap part; then the electrode group is smashed by pressurizing from a direction orthogonal to the thin plate; and the electrode group molded is inserted in this way into a case of the square- type battery.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a prismatic battery, and more particularly, to a method for manufacturing a prismatic battery using an electrode group in which a sheet-shaped positive electrode and a sheet-shaped negative electrode are flatly wound via a separator. About.

[0002]

2. Description of the Related Art In recent years, in response to demands for miniaturization, weight reduction, and long life of portable devices such as notebook personal computers and cellular phones, small, lightweight and highly efficient prismatic batteries such as prismatic lithium secondary batteries have been developed. Development of things is desired.

In a conventional prismatic lithium secondary battery, a sheet-shaped positive electrode, a separator, and a sheet-shaped negative electrode are spirally wound using a flat or flat rhombus-shaped core, and these are used as an electrode group to form a rectangular battery can. Has been inserted. When the electrode group is wound, in order to increase the winding density of the positive / negative electrode and the separator, these are wound under a predetermined tension. In the above, a large tension was applied to the electrode and the separator, and the electrode was sometimes broken by this tension. Therefore, in order to alleviate this tension, a flat plate or a rhombic winding core is rounded at the vertex in the major diameter direction, and measures are taken to increase the radius of curvature as much as possible.

[0004]

In order to insert the electrode group wound in this manner into a flat rectangular battery case, the electrode group is pulled out of the electrode group, and then the electrode group is perpendicular to the longitudinal direction. It has been practiced to press and crush the sheet in a desired direction to make it as flat as possible before inserting it into a battery case. However, when the electrode group wound by the above-mentioned conventional method is crushed, as shown in FIG.
As shown in the partially enlarged view of FIG. 3, the inner circumferential bent portions at both ends in the longitudinal direction are bent into an irregular shape.
The bent portion may be bent into a triangular cross section, and the triangular corner may be hard and sharp. In this state, the wound electrode group is inserted into the battery case and through a predetermined process,
When a battery is manufactured, pressure is applied to this part due to the expansion and contraction of the electrode generated during the charge and discharge cycle, so that the positive electrode and the negative electrode short-circuit through the separator at the corner, and the battery voltage is reduced during storage of the battery. May cause a decline.

The present invention has been made in view of the above-mentioned problems, and has as its object to avoid a short circuit between a positive electrode and a negative electrode of a battery by improving a manufacturing process of an electrode group and to reduce a voltage during storage of the battery. It is an object of the present invention to provide a method for manufacturing a prismatic battery that does not cause the problem.

[0006]

In order to achieve the above object, in the present invention, a sheet-shaped positive electrode, a separator and a sheet-shaped negative electrode are wound around a flat core to form a spiral electrode group,
After the core is pulled out, a thin plate is inserted in the center gap of the electrode group instead of the core, and the thin plate is brought into contact with the inner peripheral bent portion of the electrode group at both ends in the longitudinal direction of the center gap, Thereafter, the electrode group is pressed and crushed from a direction perpendicular to the thin plate, and the electrode group formed in this manner is inserted into a prismatic battery case. In this way, by inserting the thin plate into the center gap of the electrode group and then crushing the electrode group, the inner peripheral bent portion of the electrode group is bent regularly along the end of the thin plate and becomes almost flat. Since the battery is folded, a short circuit between the positive and negative electrodes of the battery can be avoided.

Preferably, the thin plate having a width smaller than the length of the central gap in the longitudinal direction is used, and the thin plate is pressed against one of the inner bent portions of the electrode group. The portion is pressed and crushed as described above, and then the thin plate is crushed in the same manner as described above in a state where the thin plate is pressed against the other of the inner bent portions, so that the thin plate is formed in the center gap portion of the wound electrode group. Insertion work can be facilitated.

Preferably, the central portion of the thin plate is bent or curved, and when pressed from a direction perpendicular to the surface thereof, the thin plate is deformed flat and has a width corresponding to the length of the central gap in the longitudinal direction. The thin plate is inserted into the central gap with its central portion bent or curved, and then the electrode group is pressed and crushed, whereby the electrode Only one pressurization step is required to crush the group.

Preferably, a stainless steel plate having a thickness of 0.1 to 0.5 mm is used as the thin plate.

[0010]

Preferred embodiments of the present invention will be described below with reference to the accompanying drawings. First, a method for manufacturing a wound electrode group according to the present invention will be described.

The cathode is prepared by dispersing 91 parts by weight of LiCoO _{2 as an} active material, 6 parts by weight of graphite as a conductive material, and 3 parts by weight of polyvinylidene fluoride as a binder in N-methyl-2-pyrrolidone as a solvent. A slurry was formed. The positive electrode slurry thus prepared was uniformly coated on an aluminum foil (thickness: 20 μm) as a current collector, dried, and then rolled with a roll press to obtain a positive electrode sheet.

The negative electrode is a carbon material (natural graphite) as an active material.
90 parts by weight and polyvinylidene fluoride 10 as a binder
Parts by weight were dispersed and mixed with N-methyl-2-pyrrolidone as a solvent to form a slurry. The negative electrode slurry thus prepared was uniformly applied on a copper foil (thickness: 10 μm) as a current collector, dried, and then rolled by a roll press to obtain a negative electrode sheet.

The above-mentioned positive electrode and negative electrode were wound around a core having a rhombic shape many times through a separator made of a microporous polyethylene film having a thickness of 25 μm. The core is pulled out of the electrode group around which the core is wound, a thin plate having a thickness of 0.1 mm is inserted into the center gap of the electrode group, and the plate is folded inward at both ends in the longitudinal direction of the center gap. The electrode group was brought into contact with the curved portion, and then the electrode group was crushed by a press from a direction perpendicular to the thin plate.

FIG. 1 shows a first embodiment in which the above-mentioned electrode group is crushed according to the present invention. Reference numeral 1 denotes a spirally wound electrode group, and a central gap 2 of the electrode group is formed in a longitudinal direction of the gap. A thin plate 3 having a width of about 1/2 of the length is inserted. As this thin plate, a stainless steel plate having a thickness of 0.1 to 0.5 mm is used.

In this embodiment, as shown in FIG. 1A, the electrode group 1 is pressed in the direction of the arrow while the thin plate 3 is positioned at the left end of the center gap 2 of the electrode group 1, and the electrode group 1 is pressed. The left half is crushed, and then the thin plate 3 is pressed against the right end of the center gap 2 of the electrode group to press the electrode group 1 in the direction of the arrow as shown in FIG. Shows a method of completing the crushing process of the electrode group 1 in two steps.

FIG. 2 (a) shows a thin plate 3a whose central portion is slightly bent into a mountain shape.
After the rhombic core is pulled out of the electrode group, the core is inserted into the center gap 2 of this electrode group. Next, FIG.
When the electrode group 1 is pressed by a press as shown by the arrow in (b), the thin plate 3a is deformed flat. If the width when the thin plate 3a is deformed flat is set to the same size as the length in the longitudinal direction of the center gap 2 when the electrode group 1 is crushed, the inner peripheral bent portion in the center gap of the electrode group 1 is formed. Abuts against the end of the thin plate and is folded into a predetermined shape along the end. still,
The thin plate in this embodiment may be an elastic thin plate curved in a mountain shape instead of being bent in a mountain shape.

The thin plate is preferably made of a hard material such as stainless steel in consideration of the strength of the material, and the thickness is preferably in the range of 0.1 mm to 0.5 mm.
If the thin plate is out of this range and becomes thicker, the electrode in the center gap portion of the wound electrode group becomes difficult to bend in the inner circumferential bent portion, and if it becomes thinner outside this range, the strength of the thin plate itself becomes weaker and the inner circumferential bending of the electrode becomes weaker. This is because it becomes difficult to define the bending in the curved portion.

The wound electrode formed as described above was inserted into a metal case having a width of 34 mm, a thickness of 8 mm and a height of 48 mm. As the electrolytic solution, a solution prepared by dissolving lithium hexafluorophosphate at a concentration of 1 mol / liter as a solute in a solvent in which ethylene carbonate and diethyl carbonate are mixed at a volume ratio of 1: 3, is used. Was injected into a metal case, and then sealed to form a lithium secondary battery.

Next, as a comparative example, in the manufacturing process of the battery of the present invention, when the spirally wound electrode group was pressed by a press machine, the spirally wound electrode group was crushed without inserting anything into the center thereof. A lithium secondary battery was manufactured using the electrode group.

Table 1 shows the numbers of the batteries of the present invention [Embodiment 1] and [Embodiment 2] and the batteries of the comparative example whose battery voltage was reduced during storage at room temperature.

[0021]

[Table 1]

The test conditions were 4.2 V, 1 A constant current and constant voltage charging, and the battery was stored at room temperature.
Those which became lower than 0V were confirmed. Some of the batteries of the comparative example showed a decrease in battery voltage during storage at room temperature, but the batteries of the present invention [Embodiment 1] and [Embodiment 2] were not observed.

[0023]

According to the present invention, since a thin plate is inserted into the center gap of the electrode group and then crushed, the inner peripheral bent portion of the electrode group is bent regularly along the end of the thin plate. Since the battery is folded almost flat, a short circuit between the positive and negative electrodes can be avoided during storage and use of the battery.

[Brief description of the drawings]

FIG. 1 is a conceptual diagram showing a step of manufacturing a wound electrode group according to a first embodiment of the present invention.

FIG. 2 is a conceptual diagram showing a step of manufacturing a wound electrode group according to a second embodiment of the present invention.

FIG. 3 is a schematic diagram showing a partially enlarged wound electrode group manufactured by a conventional method.

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Claims (4)

[Claims] 1. A sheet-shaped positive electrode, a separator, and a sheet-shaped negative electrode are wound around a flat core to form a spiral electrode group.
After the core is pulled out, a thin plate is inserted in the center gap of the electrode group instead of the core, and the thin plate abuts on the inner peripheral bent portion of the electrode group at both ends in the longitudinal direction of the center gap, Thereafter, the electrode group is pressed and crushed in a direction orthogonal to the thin plate, and the electrode group formed in this way is inserted into a prismatic battery case. 2. A thin plate having a width smaller than the length of the center gap in the longitudinal direction is used, and the upper portion of the thin plate is pressed against one of the inner peripheral bent portions of the electrode group, and the upper portion is pressed. 2. The method for manufacturing a prismatic battery according to claim 1, wherein the pressure is crushed by pressing as described above, and then the thin plate is crushed in the same manner as above while being pressed against the other of the inner peripheral bent portions. 3. A thin plate whose central portion is bent or curved, and when pressed from a direction perpendicular to its surface, is deformed flat and its width becomes equal to the length of the central gap in the longitudinal direction. 2. The method according to claim 1, wherein the thin plate is inserted into the central gap with its central portion bent or curved, and then the electrode group is pressed and crushed. Of manufacturing a prismatic battery. 4. The method of manufacturing a prismatic battery according to claim 1, wherein a stainless steel plate having a thickness of 0.1 to 0.5 mm is used as the thin plate.