JP2015041526A - Method for welding lid body and case body of power storage device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To secure airtightness (sealability) of a case by closing pin holes with a case body, a lid body and a separate member even if the pin holes are generated when the case body and the lid body are beam-welded.SOLUTION: In a method for welding a lid body 14 and a case body 13 of a secondary battery 10 (power storage battery), the lid body 14 closing an opening 13a is beam-welded to the case body 13 in a state where an electrode assembly 12 is housed in the case body 13 having the opening 13a capable of inserting the electrode assembly 12 thereinto. Then, beam irradiation is performed on an abutting part between the lid body 14 and the case body 13 from the outside thereof in a state where a place to be welded of the lid body 14 is arranged at a welding position abutting with the case body 13 and under such a condition, a thermoplastic material 24 capable of being molten by heat resulting from welding is arranged on the inner side than the abutting part between the lid body 14 and the case body 13.

Description

  The present invention relates to a method for welding a lid of a power storage device to a case body, and more specifically, in a state where the electrode assembly is accommodated in a case body having an opening into which the electrode assembly can be inserted. The present invention relates to a welding method between a lid body of a power storage device and a case body, which beam-welds a lid body to be closed to the case body.

  Power storage devices such as secondary batteries and capacitors are widely used as power sources because they can be recharged and can be used repeatedly. In general, a power storage device with a large capacity includes a case for accommodating an electrode assembly, and the electrode assembly is accommodated in the case. Conventionally, a case of a secondary battery is configured as a separate part from a case body and a lid body, and after the electrode assembly is accommodated in the case body, the lid body is formed by laser welding so as to cover the opening of the case body. Welded. When the case main body and the lid body are welded by laser welding, the pinhole generated at the boundary between the case main body and the lid body reduces the yield of the product.

  Conventionally, as shown in FIG. 7, the opening of a metal cylindrical can 50 is closed with a metal lid 52, and a terminal pin 54 is fixed to the center of the lid 52 through a sealing glass 56, There has been proposed a sealing structure for a sealed battery in which an adhesive sealing agent 60 is applied to the inner portion of the joint portion 58 with the lid 52 over the entire circumference, and the joint portion 58 is airtightly sealed primarily (Patent Document). 1). In this sealed battery, since the entire case inner portion of the joint 58 between the cylindrical can 50 and the lid 52 is primarily sealed by the adhesive sealant 60 before the laser welding, the internal electrolyte solution It is assumed that laser welding with high reliability is possible without adversely affecting the joint 58, and no welding spark is applied to the inside.

Japanese Utility Model Publication No. 61-174169

  The purpose of the adhesive sealant 60 of Patent Document 1 is to prevent the internal electrolyte from reaching the gap of the joint 58 during welding, and when a pinhole is generated during laser welding, the pinhole is prevented. It does not play a role of preventing the airtightness from being impaired by this, and there is no description regarding a case where a pinhole is generated during laser welding.

  The present invention has been made in view of the above problems, and the object thereof is to separate the pinhole from the case main body and the lid body even if a pinhole is generated during beam welding between the case main body and the lid body. An object of the present invention is to provide a method for welding a lid body of a power storage device and a case main body, which can ensure airtightness (sealing property) of the case by closing with the case.

  A method for welding a lid of a power storage device and a case main body that solves the above problem is a lid that closes the opening in a state where the electrode assembly is accommodated in a case main body having an opening into which the electrode assembly can be inserted. This is a method of welding the lid of the power storage device and the case main body, which beam-welds the body to the case main body. And the location which should weld the said cover body is arrange | positioned in the welding position which contact | abuts with the said case main body, and it can be fuse | melted by the heat accompanying welding inside the contact part of the said cover body and the said case main body in that state In a state where the thermoplastic material is disposed, the contact portion is irradiated with a beam from the outside.

  According to this configuration, the thermoplastic material disposed on the inner side of the contact portion between the lid and the case main body is melted at least on the side close to the contact portion due to heat accompanying welding during welding. When a pinhole is generated during beam welding, the melted portion of the thermoplastic material is increased, and the entire thermoplastic material in the space is in a molten state, and a part of the thermoplastic material enters the pinhole and closes the pinhole. Therefore, even if a pinhole is generated during beam welding between the case main body and the lid body, the case can be secured with airtightness (sealing performance) by closing the pinhole with a separate member from the case main body and the lid body.

  It is preferable that the inside of the case body is in a pressurized state when welding the lid and the case body. According to this configuration, when a pinhole is generated during laser welding and the entire thermoplastic material is in a molten state, the entire thermoplastic material in a molten state is subjected to a pressurizing action, so that the molten thermoplastic material is contained in the pinhole. It will surely invade and close the pinhole.

  The pressurization is preferably performed by supplying a compressed gas from a liquid injection hole formed in the lid. When supplying the compressed gas that pressurizes the inside of the case body into the case body, a dedicated hole for supplying the compressed gas may be provided, but if an injection hole for the electrolyte is used, the compressed gas supply There is no need to form a new hole or seal the hole after the beam welding is completed, and the manufacturing cost is reduced.

  According to the present invention, even if a pinhole is generated during beam welding between the case body and the lid, the case is sealed and sealed by securing the pinhole with a separate member from the case body and the lid. be able to.

The schematic perspective view of the secondary battery of one Embodiment. (A) is a schematic cross section of a secondary battery, (b) is the elements on larger scale of (a). (A) is a schematic cross-sectional view before the lid without the electrode assembly closes the opening of the case main body, and (b) is a schematic cross-sectional view when the lid and the case main body are similarly laser-welded. (A) is a schematic cross section in the state in which the thermoplastic material entered the part where the blowhole was generated, (b) is a schematic cross section showing a welding defect when the blowhole is generated. The schematic diagram which shows the temperature measurement location of the cover body at the time of the laser welding of a cover body and a case main body. (A), (b) is a fragmentary sectional view which shows the cover body and case main body of another embodiment, respectively. The partially broken front view which shows a prior art.

Hereinafter, an embodiment embodied in a secondary battery provided with a stacked electrode assembly will be described with reference to FIGS.
As shown in FIG. 1, in a secondary battery 10 as a power storage device, an electrode assembly 12 is accommodated in a case 11. The case 11 also contains an electrolytic solution (not shown). The case 11 includes a bottomed square cylindrical case body 13 having an opening 13a (shown in FIG. 2A) into which the electrode assembly 12 can be inserted, and a lid 14 that closes the opening 13a. The case body 13 and the lid body 14 are welded by laser welding as beam welding. The secondary battery 10 of this embodiment is a lithium ion battery. The case body 13 and the lid body 14 are made of an aluminum-based metal. An aluminum-based metal means aluminum or an aluminum alloy. The aluminum alloy includes, for example, aluminum as a main component and added with copper, manganese, zinc, silicon, magnesium, and the like, and also includes a heat treatment type alloy.

  As shown in FIG. 2A, the electrode assembly 12 is formed by laminating a plurality of rectangular sheet-like positive electrodes and a plurality of rectangular sheet-like negative electrodes with a sheet-like separator between the positive electrode and the negative electrode. Has been configured. In the positive electrode and the negative electrode, portions having an active material layer in which an active material is applied on both surfaces of a metal foil are formed in a rectangular shape, and tabs 12p and 12n on which no active material layer is formed are formed protrudingly. The separator is formed slightly wider than the width of the active material layer. When the secondary battery 10 is a lithium ion secondary battery, the metal foil for the positive electrode is preferably an aluminum foil, and the metal foil for the negative electrode is preferably a copper foil.

  As shown in FIG. 2A, a positive electrode terminal 15 and a negative electrode terminal 16 are electrically connected to the electrode assembly 12. The positive electrode terminal 15 is electrically connected to the positive electrode tab 12 p of the electrode assembly 12 via the conductive member 17, and the negative electrode terminal 16 is electrically connected to the negative electrode tab 12 n of the electrode assembly 12 via the conductive member 18. Has been. Further, the positive electrode terminal 15 and the negative electrode terminal 16 protrude outside the case 11 from the hole 14 a of the lid body 14. Each of the positive terminal 15 and the negative terminal 16 is attached with a ring-shaped insulating ring 19 for electrical insulation from the case 11.

  The lid body 14 is provided with a liquid injection hole 20 for injecting an electrolytic solution into the case 11 (case body 13). The liquid injection hole 20 is closed by a sealing member 21. The sealing member 21 is made of aluminum metal and is welded to the lid body 14.

  The lid 14 is provided with a safety valve 22 that opens when the pressure in the case 11 rises to a set pressure. The safety valve 22 is made of an aluminum-based metal, and is attached to a safety valve attachment hole 23 formed in the lid body 14 by welding.

  As shown in FIGS. 2 and 3, a stepped portion 13 b is formed in an annular shape along the inner periphery of the upper end portion of the case body 13, and a stepped portion 14 b is formed on the periphery of the lid 14 on the side facing the case body 13. ing. The step portion 14 b is formed to have the same height as the step portion 13 b and the width is formed to be greater than the thickness of the case body 13. Then, in a state where the lid body 14 is placed on the case main body 13, the square annular space S in a state of communicating with the inside of the case by the stepped portion 13 b of the case main body 13 and the stepped portion 14 b of the lid body 14. Is formed, and the thermoplastic material 24 is arranged in the space S. This state is a state in which a portion to be welded of the lid body 14 is disposed at a welding position where the lid body 14 contacts the case main body 13, and the thermoplastic material 24 disposed inside the contact portion between the lid body 14 and the case main body 13. Can be melted by heat accompanying welding. The thermoplastic material 24 is preferably a low melting point alloy. As the low melting point alloy, for example, a Sn (tin) alloy is used.

Next, a method of welding the case body 13 and the lid body 14 of the secondary battery 10 in which the electrode assembly 12 is accommodated in the case 11 configured as described above will be described.
When the lid 14 is welded to the case main body 13, the electrode assembly 12 is inserted into the case main body 13 from the opening 13 a of the case main body 13, and then the lid 14 is arranged so as to close the opening 13 a of the case main body 13. To do. As shown in FIG. 3A, the lid body 14 in a state in which the thermoplastic material 24 is fitted to the stepped portion 14b is lowered from above the opening 13a of the case body 13, and as shown in FIG. The upper end surface of the case body 13 comes into contact with a part of the stepped portion 14b of the lid body 14, and the thermoplastic material 24 is disposed in the space S formed by the stepped portion 13b and the stepped portion 14b. In addition, illustration of the electrode assembly 12 is abbreviate | omitted in FIG. 3 (a), (b).

  Next, as shown by a two-dot chain line in FIG. 3B, a pipe 25 that supplies compressed gas to the injection hole 20 is connected, and compressed gas is supplied from the pipe 25 to pressurize the inside of the case 11. Thus, the laser beam is applied to the contact portion between the lid 14 and the case body 13 from the outside, and laser welding is performed. The thermoplastic material 24 disposed on the inner side of the contact portion between the lid body 14 and the case body 13 is melted at least on the side close to the contact portion by heat accompanying welding during laser welding.

  A pinhole is generated due to poor welding in a state where the portion to be welded to the lid 14 and the case body 13 is melted by the heat generated by the laser beam applied to the contact portion between the lid 14 and the case body 13. There is a case. In the conventional welding method in which the thermoplastic material 24 does not exist, the airtightness of the case 11 is impaired by the presence of the pinhole after the completion of welding when the pinhole is generated, and the secondary battery 10 becomes a defective product.

  On the other hand, when the thermoplastic material 24 is present, the thermoplastic material 24 disposed in the space S is melted at a portion close to the lid 14 and the case body 13 during laser welding, and when a pinhole is generated, the molten portion of the thermoplastic material 24 is melted. Increases, and the entire thermoplastic material 24 in the space S is in a molten state. And as shown to Fig.4 (a), the thermoplastic material 24 of a molten state penetrate | invades in the pinhole 26 by the pressurization effect | action of compressed gas, and will be in the state which plugs up the pinhole 26. FIG.

  Also, as shown in FIG. 4B, when welding the lid 14 and the case body 13 without any trouble and no pinholes are generated, a part of the thermoplastic material 24 is melted during the welding. However, after welding is completed, the original state is obtained, and the lid body 14 and the case main body 13 are welded via the welded portion 27.

  When the pinhole 26 is generated at the time of welding, in order for the molten thermoplastic material 24 to enter the pinhole 26 and close the pinhole 26, the molten thermoplastic material 24 needs to enter the pinhole 26. For this purpose, the portion corresponding to the pinhole 26 of the thermoplastic material 24 is in a molten state in a state where the pinhole 26 is generated, and it is necessary to flow toward the pinhole 26 by the pressure in the case 11.

  During laser welding, part of the heat generated by the irradiated laser is transmitted to the non-welded portions of the case main body 13 and the lid body 14, and the amount of heat used for welding is reduced accordingly. Therefore, when the pinhole 26 is generated during welding, whether or not the molten thermoplastic material 24 enters the pinhole 26 and satisfies the condition for closing the pinhole 26 as described above is determined. It cannot be judged only by the melting point. Therefore, laser welding is performed using the case main body 13 and the lid 14 to be welded, the temperature of the inner peripheral edge of the lid 14 is measured, and the stepped portion 13b of the case main body 13 and the lid are measured based on the measured temperature. The size of the 14 step portions 14b and the size of the thermoplastic material 24 are set.

  As shown in FIG. 5, in the position corresponding to the both terminal portion attachment positions (the positions indicated by circles) of the lid body 14 and the intermediate portion thereof, in the vicinity (the lid) of the stepped portion 14 b on the back side (inner surface side) of the lid body 14. A thermocouple was placed 1 mm from the end of the body 14), and the temperature during laser welding was measured. Note that the width of the stepped portion 14b was about 1 mm. Laser welding was performed in such a manner that the laser beam irradiation position moved in the order of CH1 to CH6 starting from the left end as indicated by an arrow in FIG.

  The case main body 13 and the lid body 14 were made of pure aluminum, and welding was performed with a laser output: about 3600 [W], a feed rate: 3 [m / min], and a spot diameter Φ: about 1.2 [mm]. Table 1 shows the average measured temperature at each position.

From the results in Table 1, it can be seen that the maximum temperature varies depending on the position even if the distance from the end of the lid 14 is the same. Accordingly, the case body 13 and the lid body 14 used for the secondary battery 10 as a product are measured for temperature change during laser welding at the position where the thermoplastic material 24 is disposed, and are used for the thermoplastic material 24 based on the result. If a low-melting-point alloy is set, an appropriate material is obtained.

According to this embodiment, the following effects can be obtained.
(1) The welding method of the lid 14 and the case main body 13 of the secondary battery 10 (power storage device) accommodates the electrode assembly 12 in the case main body 13 having an opening 13a into which the electrode assembly 12 can be inserted. In this state, the lid 14 that closes the opening 13 a is beam welded to the case body 13. A thermoplastic material that can be melted by the heat accompanying welding inside the contact portion between the lid body 14 and the case body 13 at a position where the lid body 14 is to be welded is disposed at a welding position in contact with the case body 13. In the state where 24 is arranged, the beam is irradiated from the outside to the contact portion between the lid 14 and the case main body 13. Therefore, even if a pinhole 26 is generated during beam welding between the case main body 13 and the lid 14, the airtightness of the case 11 can be achieved by closing the pinhole 26 with the thermoplastic material 24, which is a separate member from the case main body 13 and the lid 14. (Sealability) can be secured.

  (2) When the lid 14 and the case body 13 are welded, the inside of the case body 13 is brought into a pressurized state. According to this configuration, when the pinhole 26 is generated during laser welding and the entire thermoplastic material 24 is in a molten state, the entire molten thermoplastic material 24 is subjected to a pressurizing action, whereby the molten thermoplastic material 24 in a molten state is obtained. Surely enters the pinhole 26 and closes the pinhole 26.

  (3) Pressurization is performed by supplying compressed gas from the liquid injection hole 20 formed in the lid body 14. In the case of supplying compressed gas that pressurizes the inside of the case body 13 into the case body 13, a dedicated hole may be provided for supplying compressed gas, but if the electrolyte injection hole 20 is used, the compressed gas is compressed. There is no need to newly form a gas supply hole or seal the hole after the end of beam welding, and the manufacturing cost is reduced.

The embodiment is not limited to the above, and may be embodied as follows, for example.
The lid body 14 and the case main body 13 are not limited to the configuration in which the lid body 14 is fitted to the case main body 13 and joined by laser welding so that the welded portion is the peripheral surface of the case 11. For example, as shown in FIG. 6A, the height of the stepped portion 13b formed inside the upper end portion of the case main body 13 is set to be the same as the thickness of the lid body 14, and the upper surface of the lid body 14 and the case main body 13 are set. The lid body 14 and the case body 13 are welded by laser welding in a state where the upper end surface of the lid body 14 is located on the same plane and the peripheral surface of the lid body 14 is in contact with the stepped portion 13b of the case body 13. May be. In this case, during welding, the beam is irradiated from above the case 11 toward the contact portion between the lid body 14 and the case body 13.

  The lid 14 is not limited to the structure welded to the case body 13 in a state of being fitted to the opening of the case body 13, but is mounted on the opening side end surface of the case body 13 without being fitted to the opening. The structure may be welded to the case body 13. For example, as shown in FIG. 6B, in order to form a space S in which the thermoplastic material 24 is arranged, the groove 28 in a state where a part of the back surface of the lid body 14 faces the opening side end surface of the case body 13. May be formed.

  ○ When the lid 14 and the case main body 13 are welded, the supply of compressed gas that pressurizes the inside of the case main body 13 is not performed from the liquid injection hole 20 formed in the lid 14, but the case main body 13 or the lid A hole for supplying compressed gas may be provided in the body 14, and compressed gas may be supplied from the hole. However, it is preferable to use the liquid injection hole 20.

  A centrifugal force may be applied to the thermoplastic material 24 as a method of applying a force that causes the molten thermoplastic material 24 to enter the generated pinhole 26 when the lid 14 and the case body 13 are welded. For example, welding is performed in a state where the laser welding apparatus is rotated around the center of the case body 13 together with the case body 13 and the lid body 14 as the center of rotation.

  ○ When welding the lid body 14 and the case body 13, the case body 13 and the outside of the lid body 14 are in a reduced pressure state as a method of applying a force that causes the molten thermoplastic material 24 to enter the generated pinhole 26. May be.

The thermoplastic material 24 is not limited to a low melting point alloy, and may be a thermoplastic resin, for example.
The case main body 13 is not limited to a bottomed cylindrical shape, and may be a cylindrical shape having openings 13a on both sides, and lids 14 existing on both ends of the case main body 13.

The lid 14 is not limited to a plate shape, and may be a shallow bottomed cylindrical shape.
The thermoplastic material 24 is not limited to a quadrangular cross section, and may have another shape, for example, a triangular shape.

The case body 13 and the lid body 14 are not limited to aluminum-based metal, and may be made of, for example, stainless steel.
○ Beam welding is not limited to laser welding, but may be electron beam welding.

The electrode assembly 12 is not limited to the laminated type, and may be a wound type.
The secondary battery 10 does not require an electrolytic solution, and may be configured to use an electrolytic solution as an electrolyte, or may be configured to use a solid electrolyte or a polymer electrolyte without using an electrolytic solution.

The power storage device is not limited to the secondary battery 10 and may be a capacitor such as an electric double layer capacitor or a lithium ion capacitor.
The following technical idea (invention) can be understood from the embodiment.

(1) A power storage device in which the electrode assembly is housed in a case body having an opening into which the electrode assembly can be inserted, and a lid that closes the opening is welded to the case body.
A thermoplastic material that can be melted by heat accompanying welding is arranged inside the welded portion of the lid and the case body, and the thermoplastic material is in a state of entering the pinhole formed in the welded portion. A power storage device.

  DESCRIPTION OF SYMBOLS 10 ... Secondary battery as an electrical storage device, 12 ... Electrode assembly, 13 ... Case main body, 13a ... Opening part, 14 ... Cover body, 20 ... Injection hole, 24 ... Thermoplastic material.

Claims (3)

A power storage device lid and a case main body that beam-welds a lid that closes the opening to the case main body in a state where the electrode assembly is accommodated in a case main body having an opening into which the electrode assembly can be inserted. A welding method,
A thermoplastic material which is disposed at a welding position where the portion to be welded of the lid is in contact with the case main body and can be melted by heat accompanying welding inside the contact portion between the lid and the case main body in that state. A method of welding the lid of the power storage device and the case main body, wherein the contact portion is irradiated with a beam from the outside in a state where the contact portion is disposed.   The method for welding the lid of the power storage device and the case main body according to claim 1, wherein the inside of the case main body is in a pressurized state at the time of welding the lid and the case main body.   The method of welding the lid of the power storage device and the case body according to claim 2, wherein the pressurization is performed by supplying a compressed gas from a liquid injection hole formed in the lid.