JP4946098B2 - Bonding structure of ultrasonic bonding - Google Patents

Description

  The present invention relates to a bonding structure of ultrasonic bonding in the case where ultrasonic bonding is performed by applying ultrasonic vibration while pressing and bonding the bonding surfaces of two plate-like members.

  In recent years, in response to growing environmental awareness, there is a movement to shift the power source of automobiles from an engine using fossil fuel to a motor using electric energy. For this reason, the technology of the battery that serves as a power source for the motor is also rapidly developing.

  An automobile is desired to be equipped with a battery that is small and light and can be charged with a large amount of power frequently and has excellent vibration resistance and heat dissipation. In response to this demand, recently, an assembled battery in which a large number of flat type cells are connected in series has been developed. When used as a driving application for automobiles or the like, a large amount of energy is required, so that it is necessary to increase the size of each unit cell, and the battery weight increases accordingly.

Examples of the assembled battery include a lithium ion battery module, which is used by connecting a large number of positive electrode tabs and negative electrode tabs of a flat unit cell in series by ultrasonic bonding. And the joining technique of such an ultrasonic joining is proposed by patent document 1 and patent document 2. FIG.
JP 2000-260478 A Japanese Patent Laid-Open No. 10-225779

  By the way, when connecting the cells in series, the electrode tabs of one unit cell and the other unit cell are ultrasonically bonded to each other, but at the time of ultrasonic bonding, the electrode tab (particularly the root portion of the unit cell) is used. There is a problem that stress is applied.

  Further, in an assembled battery in which a large number of single cells are connected in series, since the individual single cells tend to increase in size, the weight of the assembled battery tends to be applied to the electrode tab where the joint exists. Therefore, when vibration is applied to the automobile while traveling on a rough road, there is a problem that the assembled battery mounted on the automobile is also vibrated, and tension due to vertical vibration is applied to the electrode tab.

  The present invention has been made to solve the above-described problems of the prior art, and is an ultrasonic bonding that prevents excessive stress from being applied to two plate-like members even when vibration is applied. It is an object to provide a joint structure.

In order to achieve the above object, a joining structure of ultrasonic bonding according to the present invention includes a plurality of unit cells stacked in the stacking direction of a power generating element included in a unit cell, and two adjacent unit cells adjacent to each other. The bonding structure of ultrasonic bonding is to ultrasonically bond the bonding surfaces by applying ultrasonic vibration to the bonding surfaces while superimposing and pressing the bonding surfaces of the two electrode tabs extending in the same direction. Each of the two electrode tabs extending in the same direction from the two unit cells of each pair, and an end where one of the electrode tabs is fixed and a joint where the joint surfaces are ultrasonically joined to each other The two electrode tabs that form a stress absorbing portion that can absorb the stress applied between the end portion and the joint portion and extend in the same direction from the two unit cells of each pair, , Spaced substantially parallel to each other from the end Each of the stress absorbing portions is bent toward one side of the two electrode tabs from the extending direction toward the joint portion between the end portion and the joint portion. Each stress absorbing portion is formed on an electrode tab on a side having a high bending strength, and each stress absorbing portion absorbs stress applied by ultrasonic bonding and vibration applied during traveling. To do.

  In the joining structure of ultrasonic joining according to the present invention, stress applied between the end portion and the joining portion can be absorbed in one of the two plate-like members having the joining surfaces superimposed. A stress absorbing portion is formed. Therefore, even if vibration is applied to the two joined plate-like members, the stress absorbing portion absorbs the stress that is applied to the bonded portion by the vibration, so that no extra stress is applied to the bonded portion.

  In order to achieve the above object, the ultrasonic bonding method according to the present invention provides ultrasonic vibration while applying pressure by superimposing the respective bonding surfaces of the two plate-like members having one end fixed thereto, It is a joining method in the case of joining the joining surfaces, a step of forming a stress absorbing member on at least one of the two plate-like members, a step of ultrasonically joining the two plate-like members, It is characterized by including.

  The bonding method of ultrasonic bonding according to the present invention can also obtain the same effects as those of the bonding structure of ultrasonic bonding according to the present invention.

  According to the joining structure of ultrasonic joining and the joining method of ultrasonic joining according to the present invention having the above-described configuration, the end is fixed between the fixed end of one plate-like member and the joined part. Since the stress absorbing portion capable of absorbing the stress applied between the portion and the joint portion is formed, even if vibration is applied to the two joined plate-like members, the stress absorbing portion is moved to the end portion or the joint portion by vibration. It is possible to absorb the stress to be applied and prevent an excessive stress from being applied to the plate-like member.

  Moreover, according to the joining method according to the present invention, even when vibration is applied to the battery, the stress at the joined portion can be relaxed by the stress absorption at the stress absorbing portion.

  Below, the joining structure of ultrasonic joining concerning the present invention is explained in detail based on a drawing.

  FIG. 1 is a cross-sectional view of an assembled battery to which the ultrasonic wave bonding structure of this embodiment is applied, and FIG. 2 is a perspective view of a single battery.

  The unit cell 20 is a battery formed in a flat shape as shown in FIG. A plurality of power generation elements (not shown) in which a positive electrode layer, a negative electrode layer, and an electrolyte layer are laminated between these electrode layers are included in the flat battery body 26. The single battery 20 is a secondary battery such as a lithium ion secondary battery, for example. In the assembled battery 10, the unit cells 20 are stacked in the same direction as the stacking direction of the power generation elements included.

  The unit cell 20 includes a positive electrode tab 22 and a negative electrode tab 24 that extend from a flat battery body 26 that encloses a power generation element. The negative electrode tab 24 is formed of an aluminum thin plate. The positive electrode tab 22 is formed of a copper thin plate. And the several cell 20 is laminated | stacked so that the positive electrode tab 22 and the negative electrode tab 24 may become alternate in the lamination direction.

  The unit cells 20 are fixed to each other by attaching a double-sided tape or an adhesive to the flat battery body 26. In the uppermost cell 20, the negative electrode tab 24 is connected to a positive electrode terminal (not shown), and in the lowermost cell 20, the positive electrode tab 22 is connected to a negative electrode terminal (not shown).

  Thus, the assembled battery 10 is assembled by stacking up and down by sequentially connecting the positive electrode tab 22 and the negative electrode tab 24 of the adjacent unit cells 20 in series, and an ultrasonic bonding apparatus is used for the bonding.

  FIG. 3 is a schematic diagram illustrating an example of an ultrasonic bonding apparatus. As shown in FIG. 3, the ultrasonic bonding apparatus 30 includes an anvil 40 that sandwiches two plate members and a bonding tool called a horn 50, and is particularly suitable for bonding dissimilar metals. As described above, since the material of the negative electrode tab 24 is aluminum (Al) and the material of the positive electrode tab 22 is copper (Cu), ultrasonic bonding is suitable for these bondings.

  The anvil 40 is a pedestal on which two plate-like members to be joined (for example, the positive electrode tab 22 and the negative electrode tab 24) are placed, and a plurality of protrusions 41 are formed on the holding surface. The horn 50 can adjust the relative position with respect to the anvil 40 as appropriate, and a plurality of protrusions 51 are also formed on the holding surface. Further, the horn 50 is provided with a pressurizing means 60 that presses the horn 50 from the rear in the clamping direction. At the time of ultrasonic bonding, the horn 50 generates ultrasonic vibration while pressing the two plate-like members placed on the anvil 40 with a constant pressure.

  That is, the ultrasonic bonding apparatus 30 causes the two plate-like members to reciprocate linearly by ultrasonic vibration by the horn 50, and the contact surfaces of the plate-like members are rubbed together, so that an oxide film or the like on the member surface can be obtained. Impurities are removed to expose and contact a beautiful metal surface, and two plate-like members are solid-phase bonded by frictional heat generated at that time.

  An assembled battery such as a lithium ion secondary battery is assembled using the ultrasonic bonding apparatus 30 as described above. In this case, a bonding structure as described below is adopted in the present embodiment. FIG. 4 is a schematic diagram of a joining structure of ultrasonic joining according to the present embodiment. For convenience of explanation, a case where two sets of unit cells are connected in series will be described.

  As shown in FIG. 4, two sets of unit cells 20 are stacked one above the other in the same direction as the stacking direction of the power generating elements contained therein. For example, the positive tab 22 of the upper unit cell 20 is replaced with the negative tab 24 of the lower unit cell. 2 sets of unit cells 20 are connected in series. Prior to ultrasonic bonding, a stress absorbing portion 70 that can be separated from the negative electrode tab 24, which is one plate-like member, before the bonded portion to absorb stress applied to the bonded portion, such as bending force and stretching force, is formed. ing. In the present embodiment, the stress absorbing portion 70 is formed by a bent portion, and is formed in a crank shape (key shape) by bending the upper negative electrode tab 22 obliquely downward from the extending direction toward the joint portion. ing. That is, the positive electrode tab 22 of the upper unit cell 20 and the negative electrode tab 24 of the lower unit cell are separated from each other in the stacking direction. Is superposed on the negative electrode tab 24 of the unit cell 20 and is ultrasonically bonded so that the bonding portion 71 is positioned on the end side thereof.

  Thus, in the joining structure of ultrasonic joining according to the present embodiment, one of the two plate-like members (for example, the positive electrode tab 22 and the negative electrode tab 24) on which the joining surfaces are superimposed (for example, the positive electrode tab 22 and the negative electrode tab 24). The bent forming portion 70 is formed so as to be able to absorb the stress applied to the joining portion 71 by being separated from the joining portion of the positive electrode tab 22). Therefore, for example, even when high-frequency vibration transmitted from the joint portion is applied during ultrasonic joining, or when the assembled battery 10 is mounted on a vehicle and travels on a rough road or the like, the two plate-like members joined together Even if vertical vibration is applied to the (positive electrode tab 22 and the negative electrode tab 24), the bent molded portion 70 is to be applied to the joint portion (the end portion of the positive electrode tab 22) between the unit cell 20 and the positive electrode tab 22 or the joint portion 71 by vibration. Since the tension | tensile_strength to absorb is absorbed, the junction part 71 does not fracture | rupture.

  The bent shape of the bent forming portion 70 is not limited to the crank shape (key shape), and may be formed into, for example, an S shape (A) or a Z shape (B) as shown in FIG. Absent.

  When vibration is applied to two ultrasonically joined plate-like members, the plate-like member having a lower bending strength is likely to be deformed. Therefore, this bending molding is performed so that stress is absorbed by the plate-like member having a higher bending strength. The portion 70 is preferably formed before the joint portion of the plate-like member having the higher bending strength. For example, in the case where the positive electrode tab 22 made of Cu and the negative electrode tab 24 made of Al are assumed to have the same plate thickness, since the Cu material has higher bending strength, the bent forming portion 70 is formed on the positive electrode tab 22. To do. The bending strength depends not only on the material of the plate member but also on the plate thickness.

  FIG. 6 is a schematic diagram showing a modification of the joining structure of ultrasonic joining according to the present embodiment. As shown in FIG. 6, an expansion / contraction mechanism portion 73 is interposed between the bending portion 70 and the joint portion 71. As this expansion-contraction mechanism part 73, the bellows-shaped bellows by corrugation processing, dampers, such as a coil, etc. are employable, for example. In this manner, by providing the expansion / contraction mechanism 73 between the bending molded part 70 and the joint 71, not only vertical vibration but also vibrations in various directions can be positively absorbed.

  By the way, due to restrictions on the product structure, there are cases where the joining position of ultrasonic joining must be set at a position away from the plate end. In this way, when the distance (D) from the joint to the plate end becomes long (see FIG. 9), the material portion from the joint to the plate end is swung around the joint sandwiched between the anvil and the horn. Happens. In particular, when two plate-like members are thick plate members and require large joining energy, as shown in FIG. 9, cracks 80 in the thickness direction due to fatigue tend to occur at the boundary with the joint portion. . The inventors of the present invention, for example, overlaps an aluminum plate having a thickness of 0.4 mm as the upper plate 81 and a copper plate having a thickness of 0.2 mm as the lower plate 82 and has a diameter of 6 mm at a position away from the plate end. When ultrasonic bonding is performed by applying a pressure of 120 KPa to the horn and applying vibration of 50 μm in amplitude at a vibration frequency of 20 Khz for 0.2 seconds, bonding is performed in the manner shown in FIGS. 10A, 10B, and 10C. It has been confirmed that a crack 80 in the thickness direction occurs at the boundary portion of the portion 71.

  The joining structure of ultrasonic joining according to the present embodiment can also be applied to the case where the two plate-like members are thick plate members made of different materials. That is, as shown in FIGS. 7 and 10, in the upper plate 81 made of an aluminum plate, a stress absorbing portion (bending molded portion) 70 is formed at a position of 5 to 6 mm from the crack generation site in the vibration direction. The occurrence of the crack 80 can be prevented. In FIG. 7, the bent molded portion 70 is formed in a crank shape (key shape), but is not limited to this, and is formed in other bent shapes such as an S-shape and a Z-shape as described above. can do.

  Further, as shown in FIG. 8, in order to obtain a reliable stress absorbing performance, the bending angle θ of the bending formed portion 70 is preferably 45 degrees or more. By setting the bending angle θ to 45 degrees or more, the bending molded portion 70 can have a damper effect.

  The crack 80 has a low strength like an aluminum plate, and is prominent when a large bonding energy is required because it is a thick plate member. However, by incorporating the stress absorbing portion (bending molded portion) 70 at a position 5 to 6 mm from the crack occurrence site, the fatigue strength due to vibration of the joint portion 71 can be improved, and the occurrence of the crack 80 is prevented. Can do.

  That is, even when a large plate energy is required because the two plate-like members are thick plate members, the bent molded portion 70 serves as a damper by forming the bent molded portion 70 in the vibration direction. The effect of reducing the weight of the material portion swung when the thick plate member is vibrated is exhibited. Thereby, sound joining can be performed without cracking during ultrasonic joining between the boundary of the joining portion 71 and the plate end.

  According to the joining structure of the ultrasonic joining according to the present embodiment configured as described above, the joining part is separated from the joining part of one of the two plate-like members to be ultrasonically joined. Since the stress absorbing portion 70 capable of absorbing the stress applied to 71 is formed, even if vibration is applied to the two joined plate-like members, the stress that the stress absorbing portion 70 tries to apply to the bonded portion 71 due to the vibration is applied. It can absorb and prevent the joint 71 from being broken.

  In addition, when the joining structure of ultrasonic joining according to the present embodiment is applied to the assembly of a battery pack such as a lithium secondary battery, the unit cells 20 are connected to each other, so that the electrode tabs 22 and 24 are processed. Can be performed on a module-by-module basis, and the number of work steps can be reduced, and it is unlikely that processing errors of the electrode tabs 22 and 24 due to the stacking order of the unit cells 20 will occur. Furthermore, when the unit cells 20 are stacked, only the electrode tabs to be joined do not come into contact with each other. Therefore, the unit cells 20 can be collectively and safely joined.

  INDUSTRIAL APPLICABILITY The present invention can be widely applied to various manufacturing fields as a bonding structure in the case where ultrasonic bonding is performed by applying ultrasonic vibration while pressing the bonding surfaces of two plate members of the same type or different types. Since the simple structure of forming a stress absorbing portion that can absorb the stress applied to the joint portion by separating the plate-like member before the joint portion, it is a versatile joint structure.

It is sectional drawing of the assembled battery to which the joining structure of the ultrasonic joining of this embodiment is applied. It is a perspective view of a cell. It is a schematic diagram which shows an example of an ultrasonic bonding apparatus. It is a schematic diagram of the joining structure of the ultrasonic joining which concerns on this Embodiment. It is a schematic diagram which shows the other bending shape of the bending shaping | molding part in this Embodiment. It is a schematic diagram which shows the modification of the joining structure of the ultrasonic joining which concerns on this Embodiment. It is a schematic diagram in the case of applying the joining structure of the present embodiment to a thick plate member. It is a schematic diagram in the case of applying the joining structure of the present embodiment to a thick plate member. It is the schematic explaining the crack which arises when ultrasonically joining two thick board members. It is the schematic explaining the generation | occurrence | production state of the crack in a thick board member.

Explanation of symbols

10 battery packs,
20 cells,
26 Flat battery body,
22 positive electrode tab,
24 negative electrode tab,
30 ultrasonic bonding equipment,
40 Anvil,
41 protrusions,
50 horns,
51 protrusions,
60 pressure means,
70 Stress absorption part (bent molding part),
71 joints,
73 telescopic mechanism,
80 crack,
81 Upper plate,
82 Lower plate.

Claims (5)

A plurality of the unit cells are stacked in the stacking direction of the power generating elements included in the unit cells, and the joint surfaces of the two electrode tabs extending in the same direction from the two adjacent unit cells are overlapped. Applying ultrasonic vibration to the bonding surfaces while applying pressure, and a bonding structure of ultrasonic bonding for ultrasonic bonding between the bonding surfaces ,
Between each of the two electrode tabs extending in the same direction from the two cells of each pair, between the fixed end of one electrode tab and the joint where the joint surfaces are ultrasonically joined Forming a stress absorbing portion capable of absorbing stress applied between the end portion and the joint portion ;
Two electrode tabs respectively extending in the same direction from the two unit cells of each pair protrude from the end portion toward the joint portion and spaced apart from each other substantially in parallel.
Each of the stress absorbing portions is a bent molded portion formed by bending one of the two electrode tabs from the extending direction toward the bonded portion between the end portion and the bonded portion,
Each of the stress absorbing portions is formed on the electrode tab on the side having a high bending strength,
Each said stress absorption part absorbs the stress added by ultrasonic joining, and the vibration added during driving | running | working, The joining structure of ultrasonic joining characterized by the above-mentioned. Junction structure of ultrasonic bonding according to claim 1 wherein the bending angle of the electrode tabs, wherein Der Rukoto than 45 degrees of the bent forming portion. The joining structure of ultrasonic joining according to claim 1 or 2 , wherein said bending forming part includes an extension / contraction mechanism part for extending / contracting a part of said electrode tab . The ultrasonic electrode joining structure according to any one of claims 1 to 3, wherein the electrode tabs are a positive electrode tab and a negative electrode tab of a flat unit cell . Junction structure of ultrasonic bonding according to any one of claims 1 to 4, wherein the electrode tabs extending from each of the two unit cells forming the pair are different materials.

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