JP2013188787A - Welding method, and method for manufacturing storage device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To minimize the formation of blow holes in a weld part in welding work.SOLUTION: A welding method for welding the contact part of two members to be welded is carried out to weld in such a state that a part of the end of the contact part communicating with a welding action position is in contact with a low pressure space whose atmospheric pressure is lower than an atmospheric pressure in the welding action position. This welding method is used to weld a casing BC of a storage device placed in a decompressed state from the outside of the casing BC. The formation of bubbles during welding can be suppressed by a suction effect obtained by forming the low pressure space.

Description

  The present invention relates to a welding method for performing welding on contact portions of two members to be welded, and a method for manufacturing a power storage device using the welding method.

Such a welding method can be used for various welding objects such as outer containers of various apparatuses. However, in the welding operation, as described in Patent Document 1 below, bubbles are formed in the melted portion by welding. It is known that the bubbles remain as cavities even after the melted portion is solidified, and so-called blow holes (pores) may be generated.
The presence of such cavities is a factor that reduces the strength of the welded portion.
In order to avoid the generation of such cavities, for example, in Patent Document 1 below, a method of providing a gap with an appropriate size and letting the gas generated during welding escape from the gap.

JP 2000-32080 A

However, in many cases, it is difficult to ensure a sufficient gap for escaping the gas generated during welding, and even if a gap for escaping the gas is provided, there are many cases where the gas cannot always be sufficiently discharged.
The present invention has been made in view of such circumstances, and an object thereof is to suppress the occurrence of blowholes as much as possible.

  According to a first aspect of the present application, there is provided a welding method in which a welding operation is performed on contact portions of two members to be welded. Weld in a state where it is in contact with a low-pressure space at a lower atmospheric pressure.

That is, when a welding action is performed on the contact portions of two members to be welded, high-pressure bubbles are generated at the tip portion of the melted portion by welding, for example, by entraining air remaining in a slight gap between the contact portions.
At this time, if the end of the contact portion communicating with the welding position via a slight gap in the contact portion is in contact with a low pressure space having an atmospheric pressure lower than the atmospheric pressure at the welding position, the pressure difference The force to the low pressure space side acts on the melted part by welding.
Due to the action of the force, the bubbles are sucked toward the low-pressure space side or are pushed out to the low-pressure space side in the generation process of the bubbles, thereby suppressing the generation of the bubbles.

Further, in the second invention of the present application, in addition to the configuration of the first invention, the contact portion is welded by laser welding or TIG welding.
Therefore, in laser welding for condensing a laser spot at the welding position or TIG welding, the generation of the bubbles at the melted portion in the welding can be suppressed.

Further, in a third invention of the present application, in addition to the configuration of the first or second invention, the welding operation position is under atmospheric pressure, and the low-pressure space is in a reduced pressure state at atmospheric pressure lower than atmospheric pressure. Space.
Therefore, bubbles generated at the tip of the melted part by welding, or those in the process of generating the bubbles are sucked from the space in the reduced pressure state.

According to a fourth invention of the present application, in addition to the configuration of the third invention, the two members to be welded are wall bodies constituting a hollow container with an internal space closed, While welding from the side, the inner side of the container is brought into the reduced pressure state.
That is, when welding the wall body of a hollow container, the space of the pressure reduction state for welding can be easily made by making the inside of the container into a pressure reduction state.

According to a fifth invention of the present application, in addition to the configuration of the fourth invention, a through hole is formed in the container, and the inside of the container is decompressed by sucking the inside of the container from the through hole. State.
That is, when a through hole is formed in the container, the inside of the container can be in a reduced pressure state using the through hole.

According to a sixth invention of the present application, the container is a housing of a power storage device, the through hole is an injection port for an electrolyte, and the housing is welded by the welding method of the fifth invention. .
That is, the power storage device is generally formed with a liquid injection port for injecting an electrolyte into the housing of the power storage device.
Since the inside of the housing of the power storage device is brought into the reduced pressure state using the liquid injection port, a reduced pressure space necessary for welding can be easily created.

According to the first aspect of the present invention, the bubbles are sucked out toward the low-pressure space by the action of the force due to the pressure difference, or the bubbles remain by being pushed out toward the low-pressure space in the process of generating the bubbles. Therefore, the occurrence of blowholes at the welded portion can be suppressed as much as possible.
Moreover, according to the said 2nd invention, the blowhole which generate | occur | produces in a welding location by laser welding or TIG welding can be suppressed as much as possible.
In addition, according to the third aspect of the invention, since the bubbles generated at the tip of the melted part by welding or the generation process of the bubbles are sucked from the decompressed space, the generation of blowholes is further reduced. It can be suppressed more effectively.
In addition, according to the fourth aspect of the present invention, a space in a reduced pressure necessary for welding can be easily created, so that the welding operation can be simplified while suppressing the occurrence of blow holes.
Further, according to the fifth aspect, since the inside of the container can be brought into a decompressed state by using the through hole formed in the container, the space in the decompressed state necessary for welding is further increased. Can be easily produced.
In addition, according to the sixth aspect of the invention, by using the liquid injection port formed in the housing of the power storage device, it is possible to easily create a reduced pressure space necessary for welding. It is possible to simplify the welding operation while suppressing the occurrence of.

1 is an external perspective view of a secondary battery according to an embodiment of the present invention. The perspective view which shows the internal structure of the secondary battery concerning embodiment of this invention. The principal part expanded sectional view concerning embodiment of this invention

Hereinafter, an embodiment in which a welding method of the present invention is applied to a manufacturing process of a battery which is an example of a power storage device will be described with reference to the drawings.
In the present embodiment, a non-aqueous electrolyte secondary battery (more specifically, a lithium ion battery) which is an example of a secondary battery will be described as an example.

[Configuration of secondary battery RB]
As shown in the perspective view of FIG. 1, the nonaqueous electrolyte secondary battery RB of the present embodiment is configured by welding a cover portion 2 on the open surface of a bottomed cylindrical can 1. Has BC. The lid portion 2 is formed of a strip-shaped rectangular plate material, and a terminal bolt 5 that is a positive electrode terminal and a terminal bolt 7 that is a negative electrode terminal are attached to a surface on the outer side of the casing BC. It has been.
The can 1 is a flat rectangular parallelepiped in accordance with the shape of the lid 2, and thus has a flat, substantially rectangular parallelepiped shape as a whole of the casing BC.

On the inner side of the casing BC, the power generation element 3 and current collectors 4 and 6 indicated by a two-dot chain line in FIG. 2 are housed and arranged in a state of being partially immersed in the electrolyte. FIG. 2 shows the inner side of the casing BC as a perspective view looking up from the lower side with the can 1 removed.
The current collectors 4 and 6 are members for electrically connecting the power generation element 3 and the terminal bolts 5 and 7, and both are formed of a conductor.
The current collector 4 and the current collector 6 have a relationship in which substantially the same shape is arranged symmetrically, but the materials are different, and the current collector 4 on the positive electrode side is mainly composed of aluminum. The current collector 6 on the negative electrode side is formed of a material mainly composed of copper.

  The schematic shape of the current collectors 4 and 6 is such that the above-described metal material plate-like member is bent and formed in a posture along the side surface on the short side of the casing BC to have a substantially L shape. A portion extending along the surface of the lid portion 2 that is an arrangement surface of the lid portion, and a vertical posture portion that is bent 90 degrees downward near the longitudinal end portion of the lid portion 2 and extends in the normal direction of the lid portion 2. It has a continuous shape. In the vertical posture portions of the current collectors 4, 6, connection portions 4 a, 6 a for being bent further toward the power generation element 3 side and connected to the power generation element 3 are formed.

  The power generation element 3 is formed by coating an active material layer on each of a pair of electrode plates including a foil-like positive electrode plate formed in a long strip shape and a foil-like negative electrode plate formed in a long strip shape, Is formed as a so-called winding type power generation element, which is laminated in a state where the sheet is wound with a long strip separator interposed therebetween. The foil-like positive electrode plate or the like is wound around a flat winding axis, and the wound one has a flat shape in accordance with the shape of the battery casing BC.

When the active material layer is applied to the foil-like positive electrode plate and the foil-like negative electrode plate, a region where the active material layer is not applied in a narrow strip shape is left at the end portions in the width direction to form uncoated portions 3a and 3b.
When winding the foil-shaped positive electrode plate or the like, the uncoated portion 3a of the foil-shaped positive electrode plate and the uncoated portion 3b of the foil-shaped negative electrode plate protrude in opposite directions in the width direction of the foil-shaped positive electrode plate or the like. As shown schematically in FIG. 2, the uncoated portions 3a and 3b are located at both ends in the winding axis direction.
The uncoated portions 3a and 3b arranged in this way are welded to the connection portions 4a and 6a of the current collectors 4 and 6, respectively.

The lid 2 is made of metal (specifically, a metal mainly composed of aluminum), and the positive terminal bolt 5 attached to the lid 2 is electrically connected to the positive current collector 4. The terminal bolt 7 on the negative electrode side is electrically connected to the current collector 6 on the negative electrode side.
A rivet 8 is integrally formed on the head side of the terminal bolt 5, and an upper gasket 11 is sandwiched between the terminal bolt 5 and the lid portion 2 for electrical insulation and airtightness. The lower gasket 12 for electrical insulation and airtightness is sandwiched between the electric body 4 and the rivet 8 is caulked (see FIG. 2) to fix them, and the terminal bolt 5 and the current collector 4 Are electrically connected.
The negative electrode side has the same configuration, and a rivet 15 is integrally formed on the head side of the terminal bolt 7, and an upper gasket for electrical insulation and airtight maintenance between the terminal bolt 7 and the lid 2. 17, sandwiching a lower gasket 18 between the lid 2 and the current collector 6 for electrical insulation and airtightness, and caulking the rivet 15, thereby fixing them and collecting them with the terminal bolt 7. The electric body 6 is electrically connected.

[Manufacturing process of secondary battery RB]
Next, the manufacturing process of the secondary battery RB will be schematically described mainly with the assembly of the housing BC.
The lid 2 constituting the casing BC is formed of a metal plate mainly made of aluminum, a through hole through which the terminal bolts 5 and 7 are penetrated, a through hole in which the safety valve 19 is disposed, and further in the casing BC. A liquid injection port 20 which is a through hole for injecting an electrolytic solution is formed, and a stepped step is formed at the edge. This step is for engagement with the can 1.
The can body 1 is also made of the same material as the lid portion 2 and is formed into a flat bottomed rectangular cylindrical shape by a so-called deep drawing process using a metal plate (specifically, a metal mainly made of aluminum). To do.

A state in which the safety valve 19 is attached to the lid portion 2 and the upper gaskets 11 and 17 are sandwiched between the through holes for the terminal bolts 5 and 7 of the lid portion 2 on the positive electrode side and the negative electrode side, respectively, as described above. Then, the rivets 8 and 15 of the terminal bolts 5 and 7 are inserted from the outer surface of the casing BC, and the lower gaskets 12 and 18 are inserted into the rivets 8 and 15 protruding from the inner surface of the casing BC of the lid 2. And the upper ends of the current collectors 4 and 6 are inserted and the rivets 8 and 15 are caulked.
The power generation element 3 wound in a flat shape as described above is welded to the current collectors 4 and 6 assembled to the lid portion in this way. In other words, the connecting portions 4a and 6a of the current collectors 4 and 6 are inserted into the flat spiral uncoated portions 3a and 3b and welded by ultrasonic welding or the like.

The assembly on the lid part 2 side assembled in this way is inserted into the can body 1 and arranged so that the edge of the opening surface of the can body 1 abuts on the lower side of the step of the lid part 2. And the can 1 are welded.
The lid portion 2 and the can body 1 are wall bodies constituting a hollow container that closes the internal space for housing the power generation element 3 and the like, and are welded directly to the contact portions from the outside side. Acts to seal the contact portion.
This welding operation is performed by laser welding in the present embodiment. As this laser welding, it is preferable to use a fiber laser or the like that can reduce the spot diameter of the laser beam.
In the actual welding operation, with the lid 2 pressed against the can 1, the suction pipe indicated by a two-dot chain line A in FIG. 1 is connected to the liquid injection port 20 formed in the lid 2, The inside of the housing BC is sucked through the suction pipe by a vacuum pump that is omitted. By suction in the housing BC by the vacuum pump, the housing BC is in a reduced pressure state at an atmospheric pressure lower than the atmospheric pressure.
With the inside of the casing BC in a decompressed state, the laser beam LB schematically shown by a two-dot chain line in FIG. 1 is irradiated from the outside of the casing BC to the contact portion between the lid portion 2 and the can body 1 that are welding objects And scan along their boundaries.

FIG. 3A shows an enlarged cross-sectional view of the portion where the step forming portion of the edge of the lid portion 2 is in contact with the opening surface edge of the can body 1 before welding by laser welding. It is like that.
When the laser beam LB hits the contact portion between the lid 2 and the can 1, as shown in FIG. 3 (b) showing the same location as FIG. 3 (a), a melted portion MT indicated by cross hatching is generated. .

Bubbles BB caused by residual air remaining in the contact portion between the lid 2 and the can 1 may be generated at the tip of the melting portion MT. By making the inside of BC a space in a decompressed state lower than the atmospheric pressure, as shown by an arrow B in FIG. 3B, the bubbles BB disappear in a form of being drawn into the housing BC. Further, the bubble BB may not be generated by being drawn into the housing BC in the process of generating the bubble BB.
That is, the contact portion between the lid 2 and the can body is not a complete flat surface, but the surfaces having small irregularities are in contact with each other. The side communicates with a slight gap. Since a part of the end portion of the contact portion (that is, the end portion on the inner side of the casing BC) is in contact with the space in the reduced pressure state, the bubble BB is drawn by the pressure difference.

As a result, it is possible to suppress the bubble BB from remaining in the melted part MT as much as possible, and it is possible to sufficiently suppress the occurrence of blow holes after the melted part MT is solidified.
As the decompression state in the housing BC, if the decompression is not sufficient, the suction effect for the bubble BB or the generation factor of the bubbles BB is not sufficient, and if the pressure is too low, the melting part MT is drawn too much into the housing BC. Become. In the experiment, the measured pressure on the vacuum pump side was the best when set to about 0.08 MPa.

The suppression of the bubbles BB in the melting part MT also contributes to the fact that the installation environment of the casing BC is under atmospheric pressure.
The place (space) where the laser beam LB is welded is basically at atmospheric pressure even if there is a region where the pressure is locally high due to the shielding gas.
On the other hand, the inside of the casing BC is in a reduced pressure state at an atmospheric pressure lower than the atmospheric pressure, and as a result, as shown by an arrow C in FIG. A force to push into the BC is applied, and accordingly, the drawing of the bubble BB into the casing BC is also promoted.

  When the welding of the lid portion 2 and the can body 1 is completed over the entire circumference of the end of the lid portion 2 as described above, the electrolytic solution is injected into the casing BC from the liquid injection port 20, and after completion. The liquid injection port 20 is sealed with a liquid injection stopper (not shown).

[Another embodiment]
Hereinafter, other embodiments of the present invention will be listed.
(1) Although the case where the welding method of the present invention is applied to the welding of the casing BC of the secondary battery RB is illustrated in the above embodiment, the present invention can be applied to welding of various members.
(2) In the above embodiment, the metal material mainly composed of aluminum is exemplified as the material of the member to be welded (the lid portion 2 and the can body 1), but the present invention is also applied to welding of other metal materials. Can be applied.
(3) In the above-described embodiment, the welding action position located on the outer side of the casing BC is under atmospheric pressure, and the inner side of the casing BC is in a reduced pressure state, but the inner side of the casing BC is set to normal pressure. A pressure difference may be formed inside and outside the casing BC by pressurizing the outer side of the casing BC.
(4) In the above embodiment, the case where the casing BC is welded by laser welding is illustrated, but the present invention can also be applied to the case where a welding means for melting a welding location such as TIG welding is used. Even in that case, the occurrence of blow holes can be suppressed.

BC Housing 20 Injection port (through hole)

Claims (6)

A welding method in which a welding action is performed on a contact portion of two welding target members,
A welding method in which welding is performed in a state in which a part of an end portion of the contact portion communicating with a welding operation position is in contact with a low pressure space having an atmospheric pressure lower than the atmospheric pressure at the welding operation position.   The welding method according to claim 1, wherein the contact portion is welded by laser welding or TIG welding.   The welding method according to claim 1 or 2, wherein the welding operation position is under atmospheric pressure, and the low-pressure space is a space in a reduced pressure state at an atmospheric pressure lower than atmospheric pressure. The two members to be welded are wall bodies constituting a hollow container with an internal space closed,
The welding method according to claim 3, wherein the welding operation is performed from the outer side of the container, and the inner side of the container is set to the reduced pressure state.   The welding method according to claim 4, wherein a through hole is formed in the container, and the inside of the container is brought into the reduced pressure state by sucking the inside of the container from the through hole. The container is a housing of a power storage device, and the through-hole is an electrolyte injection port;
The manufacturing method of the electrical storage apparatus which welds the said housing | casing by the welding method of Claim 5.

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