JPH11144692A - Manufacture of sealed battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a manufacturing method for a sealed battery capable of holding productivity at the time of welding by a laser beam as high as possible while suppressing generation of crack caused by welding by the laser beam as much as possible, even in the case where a material such as aluminum alloy is used for an outer can and a seal plate in in the sealed battery such as a rectangular sealed battery. SOLUTION: A peripheral part of a seal plate 31 and an opening edge part 11 of an outer can are welded to each other by radiating a laser beam along a boundary line 40 defined by both parts. In a straight part 11b, a scanning speed is set up largely so as to make an overlapping rate of a laser beam spot 52a small (for example about 40%), and in an angular part 11a the scanning speed is set up small so as to make the overlapping rate of the spot 52a large (for example about 60%).

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 sealed battery having a step of sealing a metallic battery can and a sealing plate by laser welding, and more particularly to a method for manufacturing a rectangular sealed battery.

[0002]

2. Description of the Related Art In recent years, with the demand for portable equipment such as portable telephones, AV equipment, and computers, demands for higher performance of batteries have been rapidly increasing. Among them, nickel cadmium batteries, nickel hydrogen batteries, There is a great demand for a secondary battery such as a lithium ion secondary battery.

[0003] Such a battery is generally a sealed type, and as the shape of the battery, a cylindrical shape and a square shape are known. Among them, the square sealed type battery is mounted on a portable device. At that time, attention is paid to its excellent space efficiency, and there is a great demand for higher performance and higher reliability. This prismatic sealed battery is generally produced by deep drawing a metal plate to form a bottomed rectangular tube to produce an outer can. And sealed by attaching a sealing plate to the opening of the outer can. In this sealing process, the outer can and the sealing plate are sealed by pressure bonding or welding.

[0004] This sealing prevents leakage of the electrolyte and gas when the pressure in the outer can becomes high. However, the sealing greatly affects the reliability and life of the battery.
Generally, in the battery sealing process, a mechanical caulking method is widely used.However, in a rectangular sealed battery, sealing by a caulking method is often difficult, and sealing by laser welding is also often used. .

At the time of laser welding, welding is performed by scanning at a constant speed while intermittently irradiating laser light along a boundary between the outer peripheral portion of the sealing plate and the opening edge of the outer can. And, with such a sealing technique using laser welding, it is possible to realize a complete sealing of a prismatic battery and also to realize a high reliability and a long life of the battery. It is positioned as one of the core technologies that achieve high quality.

[0006] By the way, nickel-plated steel plates and stainless steel plates have been used in many cases as the outer can and the sealing plate. However, in order to reduce the weight of the battery, aluminum is now added with manganese or the like. Alloy plates have also been widely used.

[0007]

However, when an aluminum alloy plate is used for the outer can and the sealing plate, there is a problem that cracks are likely to occur in the welded portion if the sealing is performed by laser welding as described above. . This crack is
Usually, the spot of the laser beam occurs along the welding line that is scanned, but as a mechanism of crack generation,
It is considered that a portion (melt pool) that has been melted by irradiating the laser beam is pulled by thermal stress generated in the vicinity thereof during cooling, and cracks are generated.

[0008] In addition, cracks are likely to occur when an aluminum alloy plate is used, because aluminum alloy has a lower tensile strength than iron or stainless steel and has a high thermal conductivity, so that the welded portion is rapidly formed. Cooling. To solve such a problem, if the scanning speed of the laser beam is set to a low value, the rate of occurrence of cracks will be reduced. However, if the scanning speed of the laser beam is reduced, the time required for sealing is increased, which is not desirable in terms of production efficiency.

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and has been made in the case of a sealed battery such as a prismatic sealed battery in which a material such as an aluminum alloy is used for an outer can or a sealing plate. Another object of the present invention is to provide a manufacturing method capable of keeping the productivity during laser welding as high as possible while minimizing the occurrence of cracks due to laser welding.

[0010]

In order to achieve the above object, according to the present invention, a metal plate is formed into a bottomed cylindrical shape having a non-circular opening (in the case of a square battery, a squared bottomed cylindrical shape). ), An outer can is produced, a power generation element is stored in the outer can, a sealing plate is attached to an opening of the outer can, and an outer peripheral portion of the sealing plate and an opening edge of the outer can are In the method of welding and scanning by intermittently irradiating laser light along the boundary line between the two, welding and sealing are performed, and at the time of sealing, a section having a large degree of bending at the opening edge of the outer can (for a square battery, In the corner portion), the irradiation density of the laser beam was set higher than in the section having a small degree of bending (in the case of a rectangular battery, the straight portion).

Here, "metallic plate" refers to a plate made of a metal such as iron or an alloy such as an aluminum alloy. The inventors of the present invention have found that a crack during laser welding is a section (corner) having a large degree of bending at the opening edge of the outer can.
By focusing on the fact that cracks can be prevented by increasing the irradiation density of the laser beam, it is possible to reduce the occurrence of cracks associated with laser welding, It has been found that the scanning speed of light can be increased.

That is, according to the above-described manufacturing method, cracks are relatively likely to occur in sections (corners) where the degree of bending is large, so that cracks can be prevented by increasing the irradiation density of laser light. However, in this section, the scanning speed is reduced by the amount of setting the irradiation density of the laser light to be high. On the other hand, cracks are unlikely to occur in a section (linear portion) where the degree of bending is small, so that cracks can be prevented even if the irradiation density of laser light is reduced. In this section, the scanning speed can be increased by an amount corresponding to the setting of the low laser beam irradiation density.

Therefore, according to the above-described manufacturing method, the average scanning speed of the laser beam is increased as compared with the conventional case where the laser beam is irradiated at a constant scanning speed, that is, at a constant irradiation density. Can be done. At the time of laser welding, usually, the laser beam is scanned while overlapping the spots by laser light irradiation along the boundary line, so that the laser beam irradiation density is higher in a section with a large degree of curvature than in a section with a small degree of curvature. For this purpose, the overlap ratio of spots in the section with a large degree of curvature should be higher than the overlap rate of spots in the section with a small degree of curvature.

In order to adjust the spot overlap rate as described above, the scanning speed in the section having a large degree of bending may be made lower than the scanning speed in the section having a small degree of bending. In the case of a prismatic sealed battery, it is desirable that the overlap ratio of the spot at the corner is 1.5 times or more the overlap ratio of the straight portion.

The "overlap ratio" of the spot here is expressed by the following formula 1 when the spot diameter is R and the distance between the centers of the spots irradiated immediately before (ie, the spot pitch) is L. Value.

[0016]

(Equation 1)

In the case of a sealed battery in which the outer can and the sealing plate are made of an aluminum alloy, cracks are liable to occur particularly during welding. Therefore, the application of the manufacturing method of the present invention has a great effect.

[0018]

DESCRIPTION OF THE PREFERRED EMBODIMENTS [Structure of Battery] FIG. 1 is a perspective view of a sealed rectangular battery according to an embodiment of the present invention.
FIG. 1 is a top view of the rectangular sealed battery. This prismatic sealed battery is a lithium ion secondary battery, and has an electrode group 20 in which a negative electrode plate 21 and a positive electrode plate 22 are laminated via a separator 23 inside a bottomed rectangular cylindrical outer can 10. In addition, a non-aqueous electrolyte is accommodated therein, and the opening of the outer can 10 is sealed with a sealing body 30.

The outer can 10 is formed by forming a plate of an Al-Mn-based alloy into a square cylinder with a bottom. This Al-Mn-based alloy is lightweight because it contains aluminum as a main component, and has a higher tensile strength than aluminum alone due to the addition of manganese. The content of manganese is suitably about 1.0 to 1.5 wt%, and when the content of manganese is too large, workability and weldability at the time of molding an outer can decrease.

As shown in FIG. 1, the sealing body 30 has a nail-shaped negative electrode terminal 32 via an insulating packing 33 at the center of a sealing plate 31 formed so as to fit into the opening of the outer can 10. It is a configuration that penetrates and attaches. Sealing plate 31
Is a plate of the same Al-Mn alloy as the outer can 10 punched out in the same rectangular shape as the opening of the outer can 10.

The thickness of the outer can 10 and the sealing plate 31 is set as thin as possible within a range where required strength can be maintained, and is usually set to about 500 μm. A current collector 34 is mounted below the negative terminal 32 (inside the battery), and a washer 35 is mounted above the negative terminal 32 (outside the battery). The negative electrode terminal 32, the current collector 34, and the washer 35 are fixed to the sealing plate 31 by crimping while being insulated from the sealing plate 31 by the insulating packing 33.

The negative electrode plate 21 of the electrode group 20 is formed by applying a carbon layered compound (graphite powder) to a plate-shaped core, and is surrounded by a separator 23. The core of the negative electrode plate 21 and the current collector 34 are
They are connected by a lead plate 25. On the other hand, the positive electrode plate 22 of the electrode group 20 has a positive electrode mixture composed of a lithium-containing oxide (eg, lithium cobalt oxide) as a positive electrode active material and a conductive agent (eg, acetylene black) applied to a plate-shaped core. And is in direct contact with and electrically connected to the exterior can 10 also serving as a positive electrode.

The non-aqueous electrolyte is obtained, for example, by dissolving LiPF6 as a solute in a mixed solvent consisting of ethylene carbonate and dimethyl carbonate. Sealing plate 3
The outer peripheral portion of the housing 1 and the open end of the outer can 10 are sealed by laser welding. Although not shown in FIG. 1, an insulating sleeve 26 made of an insulating resin is interposed between the electrode group 20 and the sealing plate 31 (see FIG. 3). It is fixed at a fixed position in the can 10 and is prevented from contacting with the sealing body 30.

[Method of Manufacturing Battery] Next, a method of manufacturing the rectangular sealed battery will be described. First, an Al-Mn-based alloy plate is subjected to deep drawing to form a rectangular cylinder with a bottom, and the outer can 10 is manufactured. On the other hand, Al-Mn
A sealing plate 31 was produced by punching a plate of a base alloy,
The insulating packing 33, the negative electrode terminal 32 and the current collector 34 are combined and loaded, and a washer 35 is provided on the upper part of the negative electrode terminal 32.
Then, the sealing body 30 is produced by crimping and crimping.

The negative electrode plate 21 with the lead plate 25 is covered with the separator 23, and the positive electrode plate 22 and the negative electrode plate 21 are alternately laminated to form the electrode group 20. The electrode group 20 manufactured in this manner is inserted into the outer can 10, and the lead plate 25 is passed through the insulating sleeve 26 so that the current collecting plate 3
4 and electrically connected. Then, a non-aqueous electrolyte is injected into the outer can 10 to impregnate the electrode group 20.

Next, the insulating sleeve 26 is mounted on the upper part of the outer can 10, and the sealing body 30 is inserted and mounted in the opening of the outer can 10, and the sealing body 3 is mounted as described below.
Welding is performed by scanning the outer peripheral portion 0 and the opening edge portion 11 of the outer can 10 while irradiating a laser beam along a boundary 40 between the two. [Sealing by laser welding] Figure 3
FIG. 3 is a view showing a state in which the outer can is sealed by laser welding.

In the apparatus shown in FIG.
Can be driven in any direction within a plane parallel to the sealing plate 31. Then, the laser light 50 is guided to the condenser lens 51 from a laser light oscillation device (not shown) via an optical fiber. The laser light oscillation device emits light using yttrium aluminum garnet (YAG), and the laser light 50 is output in a pulse form (for example, the laser pulse repetition rate: 50p).
ps). Then, this laser beam 50 is
, And converges on the boundary 40 between the sealing plate 31 and the opening edge 11 to form a small circular spot 52.
(Spot diameter: several hundred μm).

By means of such a laser beam irradiation method, a member (such as an insulating sleeve 26) around a portion to be welded.
The spot 52 can be locally melted without thermally damaging the portion. In the portion of the spot 52 irradiated with the laser beam 50, the sealing plate 31 and the outer can 1
The zero-opening edge 11 melts to form a weld pool, which solidifies in a short time. In FIG. 3, reference numeral 60 denotes a welded portion where the molten pool has solidified.

In addition, an inert gas (nitrogen gas) is injected around the spot 52 of the laser beam 50, thereby preventing the welded portion from being oxidized. The number of repetitions of laser light and the speed of scanning of the condensing lens 51 in the laser light oscillator are controlled by the spot 52
Is adjusted so as to appropriately overlap the spot 52a irradiated immediately before. The adjustment of the overlap ratio is performed by adjusting the scanning speed of the condenser lens 51.

As described above, the laser light 5 which emits intermittently
0 is converged on the boundary line 40 by the condenser lens 51 and irradiated, while the direction along the boundary line 40 (the direction of arrow A in FIG. 3).
The converging lens 51 scans the boundary 40
The welded portion 60 is continuously formed along the line. In this way, by performing welding over the entire circumference of the boundary line 40, the sealing is completed.

Here, scanning speed control during welding,
That is, control of the overlap ratio of spots will be considered. In general, when an outer can having an open edge with a non-uniform degree of curvature is sealed by laser welding, the following relations are established. Cracks are more likely to occur at the corners 11a having a large degree of bending than at the straight portions 11b having a small degree of bending.

The reason is considered as follows. As described above, when the metal plate body is formed into a bottomed square cylindrical shape to produce the exterior can 10, in the produced exterior can 10, at the corner 11a having a large degree of bending, a straight portion having a small degree of bending is formed. 1
Residual stress is larger than 1b. During laser welding,
As the force applied to the molten pool, not only the thermal stress accompanying the laser beam irradiation but also this residual stress, cracks are likely to occur at the corner 11a where the residual stress is large.

The larger the overlap ratio of the spot 52 represented by the above equation 1 is set, the less the crack is generated. It is considered that the reason for this is that the greater the overlap ratio, the more heat is supplied from the molten pool formed by the previous irradiation, and the slower the cooling rate of the molten pool.

However, since the number of repetitions of the laser beam oscillation device is constant, the scanning speed decreases when the overlap ratio is increased. Therefore, in the present embodiment,
In order to minimize the time required to scan the entire circumference of the boundary line 40 while suppressing the occurrence of cracks while considering the relationship of Set the value as small as possible within the range that can be suppressed.

That is, the scanning speed of the condenser lens 51 is set to be large so that the overlap ratio is small (for example, 40%) in the linear portion 11b, and the overlap ratio is large (for example, in the corner portion 11a). 60%), the scanning speed of the condenser lens 51 is set low. [Analysis of Relationship between Scanning Speed of Laser Light and Thermal Stress] FIG. 4 shows the result of analyzing the relationship between the scanning speed of laser light and the thermal stress generated at the center of the spot for the battery of this embodiment. FIG.

As described above, the thermal stress generated at the center of the spot is analyzed because the thermal stress generated by laser welding is the largest at the center of the spot, and the thermal stress at the center of the spot is: This is because it is considered to be a factor of crack generation. FIG. 5 is an analysis model obtained by dividing the vicinity of the welded portion between the outer can and the sealing plate into a mesh shape.

The relationship between the scanning speed of the laser beam and the thermal stress shown in FIG. 4 is obtained by applying the finite element method to the analytical model shown in FIG. This is derived by using a thermal stress analysis simulation. In order to use the finite element method, as shown in FIG. 7, particularly near the spot of the laser beam where the temperature gradient is considered to be large, mesh division was particularly finely performed.

[0038]

(Equation 2)

[0039]

(Equation 3)

This analysis is based on the following conditions. Laser light wavelength: 1.06 μm Laser light power: 9.3 × 10 ² W Laser light spot diameter: 450 μm Pulse width: 12.0 ms Analysis time from laser light irradiation: 15.0 ms Melting point of sealing plate: 1800 K Melting point of resin of insulating sleeve 26: 600 K. The finite element method is described in "Computer Analysis of Heat and Flow", edited by The Japan Society of Mechanical Engineers, Corona (1986)
Year) can be cited as a reference.

From the analysis results shown in FIG. 4, it can be seen that the thermal stress increases as the scanning speed of the laser beam increases. According to the characteristic diagram of FIG. 4, when the scanning speed is about 15 mm / s, the thermal stress is the tensile limit of the Al—Mn-based alloy.
000 N / cm ² . Therefore, under this analysis condition, the scanning speed is set to 15 mm / s even in the linear portion.
If it is larger than this, it is expected that the crack occurrence rate will be considerably large.

[0042]

EXAMPLES (Example) A thin rectangular sealed battery for a cellular phone was manufactured based on the above embodiment. Outer can 10
The thickness of the sealing plate 31 was 500 μm. At the time of welding, the irradiated laser light has a wavelength of 1.064 μm YA.
G laser light, the pulse repetition rate was 50 pps, and the spot diameter was about 500 μm.

The scanning speed is 12.0 m for the linear portion 11b.
m / s (52% overlap ratio) and 15.0 mm
/ S (overlap rate 40%) and the corner 11a
Was performed in a combination of 10.0 mm / s (overlap rate 60%) and 5.0 mm / s (overlap rate 80%). With any combination of scanning speeds, the rate of occurrence of cracks in the manufactured batteries was less than 1%. (Experiment)

[0044]

[Table 1]

A battery before sealing was prepared in the same manner as in the example, and laser irradiation was performed on the linear portion and the corner portion at the scanning speed shown in Table 1 under the same irradiation conditions as in the example. The occurrence rate of cracks was examined. Table 1 shows the experimental results.
As shown in FIG. As can be seen from Table 1, the scanning speed was 15.0 mm / s (overlap ratio 40
%) Or less, the crack occurrence rate is low, and the scanning speed is 20.0%.
At mm / s (overlap rate 20%), the crack occurrence rate is large.

In the corners, the scanning speed is 10.0 mm /
At s (overlap rate 60%) or less, the crack occurrence rate is small, and at scanning speed 12.0 mm / s (overlap rate 52%) or more, the crack occurrence rate is large. Than this,
In the battery of the embodiment, in order to suppress the crack occurrence rate, the scanning speed in the linear portion should be set to 15.0 mm / s or less, and the scanning speed in the corner portion should be set to 10.0 mm / s or less. Considering the productivity of welding, it can be seen that it is desirable to set the scanning speed at the linear portion to 15.0 mm / s and the scanning speed at the corners to 10.0 mm / s.

The scanning speed at the linear portion is 15.0 mm /
Looking at the case of s (overlap rate 40%),
In order to reduce the scanning speed at the corner to 10.0 mm / s (overlap rate 60%) or less, the corner overlap rate must be 1.5 times or more the linear section overlap rate. Recognize. (Other Matters) In the above embodiment, the case of a lithium ion secondary battery has been described as an example, but the present invention is also applicable to a secondary battery such as a nickel-metal hydride battery or a primary battery. .

Further, in the above embodiment, the case where an aluminum alloy is used as the material of the outer can or the sealing plate has been described. The present invention is also applicable to the case where stainless steel or the like is used. Further, in the above embodiment, a highly practical square sealed battery was described.
The manufacturing method of the present invention can be widely applied not only to a rectangular sealed battery but also to a battery having a bottomed cylindrical outer can having a non-circular opening edge.

[0049]

As described above, according to the present invention, a metal plate is formed into a bottomed cylindrical shape having a non-circular opening (in the case of a square battery, a bottomed square cylindrical shape). By preparing an outer can, the power generation element is housed in the outer can, a sealing plate is attached to the opening of the outer can, and the outer peripheral portion of the sealing plate and the opening edge of the outer can are placed on the boundary line between them. In a method of manufacturing a sealed battery by scanning and welding while intermittently irradiating a laser beam along a section, in a method of manufacturing a sealed battery, at the time of sealing, a section having a large degree of bending at the opening edge of the outer can (a square shape) In the case of a battery, the irradiation density of the laser beam is set higher in the corner (in the case of the battery) than in the section having a small degree of bending (in the case of the rectangular battery, the straight portion). In addition, productivity during laser welding can be kept high.

In the case of a sealed battery in which the outer can and the sealing plate are made of an aluminum alloy, cracks are liable to occur particularly during welding. Therefore, the application of the manufacturing method of the present invention has a great effect.

[Brief description of the drawings]

FIG. 1 is a perspective view of a prismatic sealed battery according to an embodiment of the present invention.

FIG. 2 is a top view of the sealed rectangular battery of FIG. 1;

FIG. 3 is a view showing a state in which an outer can is sealed by laser welding.

FIG. 4 is a characteristic diagram showing a result of analyzing a relationship between a scanning speed of a laser beam and a thermal stress in the battery.

FIG. 5 is an analysis model obtained by dividing the vicinity of a welded portion between an outer can and a sealing plate into a mesh shape.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Outer can 11 Opening edge 11a Corner 11b Linear part 20 Electrode group 26 Insulating sleeve 30 Sealing body 31 Sealing plate 34 Current collector 40 Boundary line 50 Laser beam 51 Condensing lens

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[Procedure amendment]

[Submission date] January 22, 1998

[Procedure amendment 1]

[Document name to be amended] Statement

[Correction target item name] Claim 2

[Correction method] Change

[Correction contents]

[Procedure amendment 2]

[Document name to be amended] Statement

[Correction target item name] 0023

[Correction method] Change

[Correction contents]

The non-aqueous electrolyte is obtained, for example, by dissolving LiPF ₆ as a solute in a mixed solvent composed of ethylene carbonate and dimethyl carbonate. Sealing plate 3
The outer peripheral portion of the housing 1 and the open end of the outer can 10 are sealed by laser welding. Although not shown in FIG. 1, an insulating sleeve 26 made of an insulating resin is interposed between the electrode group 20 and the sealing plate 31 (see FIG. 3). It is fixed at a fixed position in the can 10 and is prevented from contacting with the sealing body 30.

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Keisho Yamamoto 2-5-5-Keihanhondori, Moriguchi-shi, Osaka Sanyo Electric Co., Ltd.

Claims (6)

[Claims] 1. An outer can formed by molding a metal plate into a bottomed cylindrical shape having a first section at an opening edge and a second section having a larger degree of bending than the first section. An outer can manufacturing step of manufacturing an outer can, a housing step of storing a power generation element in the outer can, a sealing plate is attached to an opening of the outer can, and an outer peripheral portion of the sealing plate and an opening edge of the outer can. And a sealing step of performing welding while intermittently irradiating a laser beam along a boundary line between the two, and welding and sealing. The sealing step, wherein in the sealing step, A method for manufacturing a sealed battery, wherein the irradiation density of the laser beam is higher in the section than in the first section. 2. In the sealing step, welding is performed while scanning the laser beam irradiation while overlapping the spots along the boundary line, and the overlap ratio of the spots in the second section is defined as:
3. The method for manufacturing a sealed battery according to claim 2, wherein the overlap ratio of the spots in the first section is higher than the overlap rate. 3. The method for manufacturing a sealed battery according to claim 2, wherein in the sealing step, a scanning speed of the laser beam is set to be smaller in the second section than in the first section. 4. An outer can manufacturing step for manufacturing an outer can by forming a metallic plate into a bottomed rectangular tube shape; a storing step of storing a power generating element in the outer can; A sealing plate is attached to the opening, and the outer peripheral portion of the sealing plate and the opening edge of the outer can are welded by scanning while intermittently irradiating laser light along a boundary line between the two, thereby welding and sealing. A method of manufacturing a sealed battery comprising a sealing step, wherein in the sealing step, a laser beam irradiation density is higher at a corner of the opening edge than at a straight portion of the opening edge. Manufacturing method of sealed battery. 5. The sealed battery according to claim 4, wherein in the sealing step, the overlap ratio of the spot at the corner is 1.5 times or more the overlap ratio of the straight portion. Production method. 6. The outer can and the sealing plate are made of an aluminum alloy.
5. The method for producing a sealed battery according to any one of the above items 5.