Secondary battery, battery pack, and method for joining current collector of secondary battery

Abstract

Provided are: a secondary battery of which the defect rate can be reduced by suppressing mechanical vibration of a current collector from acting on a battery lid when performing ultrasonic welding of the current collector and a metal foil exposure section; and a battery pack.　The secondary battery has: an electrode body 13 provided with a positive electrode material and a negative electrode material; a battery container 11 which accommodates the electrode body 13; a battery lid 6 which seals the battery container; a current collector 14 which is disposed inside the battery container 11 and is joined to the electrode body 13 by ultrasonic welding; an external electrode terminal 8 which is provided on the outer surface of the battery lid 6 and is connected to the current collector 14; and a gas discharge valve 9 which is provided to the battery lid 6. One side of the current collector 14 is electrically connected to the external electrode terminal 8 and is fixed to the battery lid 6. The other side of the current collector 14 is joined to the electrode body 13. A joining region part 42 in which the current collector 14 and the electrode body 13 are joined is formed to be close to a tip part 47 on the other side of the current collector 14.

Description

Secondary battery, battery pack, and method for joining current collector plates of secondary battery

[0001] The present invention relates to a secondary battery, a battery pack incorporating such secondary batteries, and a method for joining current collector plates of a secondary battery.

[0002] Lithium-ion secondary batteries with high energy density have been developed as power sources for vehicles such as electric vehicles. Prismatic secondary batteries with high volume density are particularly well known as secondary batteries to be installed in vehicles.

[0003] This secondary battery is made by winding a positive electrode, which has a positive electrode foil coated on both sides with a positive electrode active material, and a negative electrode, which has a negative electrode foil coated on both sides with a negative electrode active material, in a flat shape with a separator interposed between them, and then housing this wound body (electrode body) and electrolyte solution in a rectangular battery container.

[0004] In such secondary batteries, metal foil exposed portions are formed at both ends of the wound body in the winding axis direction, exposing the metal foil of the positive electrode and the negative electrode, and current collector plates connected to external electrode terminals are connected to the metal foil exposed portions by welding or the like, thereby shortening the current path and reducing connection resistance. Note that secondary batteries using solid electrolytes have also been developed, and the present invention also covers these secondary batteries.

[0005] Although various methods are conceivable for welding the exposed metal foil portion and the current collecting plate described above, ultrasonic welding is generally used to join the exposed metal foil portion and the current collecting plate. For example, International Publication No. 2018 / 159197 (Patent Document 1) discloses a method of solid-state joining the exposed metal foil portion and the current collecting plate by clamping them between an ultrasonic horn and an anvil.

[0006] In Patent Document 1, a current collector plate is attached and fixed in advance to a battery lid that seals a battery can, and the current collector plate in this state is placed on the exposed metal foil portion of the wound body and set in a joining jig. Then, the current collector plate and the exposed metal foil portion are sandwiched between the anvil of an ultrasonic welding device and the current collector plate, and an ultrasonic horn is brought into contact with the exposed metal foil portion, and the current collector plate and the exposed metal foil portion are pressed together by the anvil and ultrasonic horn, and the ultrasonic horn is vibrated to solid-state weld the current collector plate and the exposed metal foil portion.

[0007] International Publication No. 2018 / 159197

[0008] The battery lid is integrally provided with a gas release valve, and when the pressure inside the battery container increases, the gas release valve opens (or ruptures) to release gas from inside the battery container, reducing the pressure inside the battery container and ensuring the safety of the secondary battery. The gas release valve is formed, for example, by forming a wall portion of the battery lid into a thin wall, or by press-fitting a separately manufactured sealing plug into a through-hole formed in the battery lid.

[0009] As described above, the current collector plate is attached and fixed to the battery lid and ultrasonically welded to the exposed metal foil portion. Therefore, mechanical vibrations generated by the ultrasonic horn used for ultrasonic welding are transmitted to the battery lid via the current collector plate. The mechanical vibrations acting on the battery lid act as an external force on the gas release valve via the battery lid (hereinafter, the external force acting from the ultrasonic horn toward the battery lid is referred to as mechanical force). Therefore, a configuration is needed to suppress the mechanical vibrations from being applied to the battery lid during ultrasonic welding.

[0010] An object of the present invention is to provide a secondary battery, a battery pack, and a method for joining a current collector plate of a secondary battery that can reduce the defect rate by suppressing the mechanical vibration of the current collector plate from acting on the battery lid when ultrasonically welding the current collector plate and the exposed metal foil portion.

[0011] The present invention is a secondary battery having an electrode body including a positive electrode material and a negative electrode material, a battery container that houses the electrode body, a battery lid that seals the battery container, a current collector plate arranged inside the battery container, an external electrode terminal provided on the outer surface of the battery lid, and a gas exhaust valve provided on the battery lid, wherein one side of the current collector plate is electrically connected to the external electrode terminal and fixed to the battery lid, the other side of the current collector plate is joined to the electrode body, and the joining region where the current collector plate and the electrode body are joined is formed in an end region located away from the one side on the other side of the current collector plate.

[0012] The present invention is a battery pack constructed by stacking a plurality of secondary batteries, each of which has an electrode body including a positive electrode material and a negative electrode material, a battery container that houses the electrode body, a battery lid that seals the battery container, a current collector plate that is disposed inside the battery container and joined to the electrode body by ultrasonic welding, an external electrode terminal that is provided on the outer surface of the battery lid and connected to the current collector plate, and a gas release valve that is provided on the battery lid, wherein the above-mentioned secondary battery is used as the secondary battery.

[0013] The present invention provides a method for joining current collector plates of a secondary battery having an electrode body including a positive electrode material and a negative electrode material, a battery container that houses the electrode body, a battery lid that seals the battery container, a current collector plate that is disposed inside the battery container and joined to the electrode body by ultrasonic welding, an external electrode terminal that is provided on the outer surface of the battery lid and connected to the current collector plate, and a gas release valve that is provided on the battery lid, wherein the ultrasonic welding is performed using an anvil that presses the current collector plate and an ultrasonic horn that presses the electrode body, the anvil is positioned close to the tip of the other side of the current collector plate opposite the side that is fixed to the battery lid, and the ultrasonic horn is positioned corresponding to the position of the anvil, and in this state, the ultrasonic horn is mechanically vibrated to form a joining area between the current collector plate and the electrode body at the position where the anvil is positioned.

[0014] According to the present invention, the propagation distance from the joining area of ​​the current collector plate to the fixing position on the battery lid can be made long, and the mechanical force caused by the mechanical vibration of ultrasonic welding acting on the battery lid is weakened or absorbed by the long propagation distance of the current collector plate, thereby suppressing damage to the gas release valve and reducing the defect rate.

[0015] FIG. 1 is an external perspective view of a battery pack in which secondary batteries of the present invention are combined. FIG. 2 is an external perspective view of a secondary battery according to an embodiment of the present invention. FIG. 3 is an external perspective view showing the configuration of the electrode body shown in FIG. 4. FIG. 5 is an external perspective view of a current collector plate according to an embodiment of the present invention before assembling the battery lid. FIG. 6 is an external perspective view of a current collector plate according to an embodiment of the present invention before assembling the battery lid. FIG. 7 is an external perspective view of a current collector plate according to an embodiment of the present invention after assembling the battery lid. FIG. 8 is an explanatory view illustrating a state in which the current collector plate and the electrode body according to an embodiment of the present invention are ultrasonically welded. FIG. 9 is an external perspective view of a current collector plate according to an embodiment of the present invention, seen from the side where the anvil contacts. FIG. 10 is an external perspective view of a modified current collector plate according to an embodiment of the present invention, seen from the side where the anvil contacts.

[0016] Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings. However, the present invention is not limited to the following embodiment, and various modifications and application examples within the technical concept of the present invention are also included within its scope.

[0017] 1 shows a battery pack in which a plurality of secondary batteries according to an embodiment of the present invention are stacked. The battery pack 100 of this embodiment is a battery pack in which flat rectangular secondary batteries 20 are arranged alternately with spacer members 2 in the thickness direction. In the following description, an XYZ Cartesian coordinate system may be used, in which the thickness direction of the secondary batteries 20 is the X-axis direction, the width direction of the secondary batteries 1 is the Y-axis direction, and the height direction of the secondary batteries 1 is the Z-axis direction.

[0018] The battery pack 100 of this embodiment comprises a plurality of secondary batteries 20, a plurality of spacer members 2 arranged between each of the secondary batteries 20, a pair of end spacer members 3 arranged to face each other at the ends in the stacking direction, a pair of end plates 4 located on the outside of the end spacers 3 and also arranged to face each other, and a pair of side plates 5 located on both sides of the end plates 4 and arranged to face each other.

[0019] The end plates may be omitted, in which case the secondary battery 20 is held by the side plates 5 .

[0020] A battery lid 6 is attached to the upper side of the secondary battery 20, and external electrode terminals, a positive external electrode terminal 8P and a negative external electrode terminal 8N, are provided on both sides in the width direction. A gas release valve 7 and a sealing plug 9 are provided between the positive external electrode terminal 8P and the negative external electrode terminal 8N. The gas release valve 7 has the function of opening to ensure safety and reducing the gas pressure when the gas pressure inside the secondary battery 20 reaches a predetermined value or higher. The sealing plug 9 also has the function of sealing the secondary battery 1 after the liquid electrolyte has been injected into it.

[0021] Fig. 2 shows the appearance of a rectangular secondary battery 20. The secondary battery 20 shown in the figure includes a battery case 11 and a battery lid 6. An electrode assembly 13 (see Fig. 4), which is a power generating body, is housed inside the battery case 11, and the upper opening of the battery case 11 is sealed by the battery lid 6. The battery lid 6 is welded to the battery case 11 by laser welding, and the battery case 11 and the battery lid 6 form a battery container.

[0022] The battery cover 6 is provided with a positive external electrode terminal 8P and a negative external electrode terminal 8N, and the electrode body 3 (see Figure 4) is charged and power is supplied to an external load via these positive external electrode terminal 8P and negative external electrode terminal 8N.

[0023] A thin-walled gas release valve 7 is integrally provided on the wall of the battery lid 6. When the pressure inside the battery container increases, the gas release valve 7 opens, releasing gas from the battery container and reducing the pressure inside the battery container. This ensures the safety of the secondary battery 20. A sealing plug 9 is welded to the battery lid 6, sealing a filler hole 10 (see FIG. 3) for injecting electrolyte into the battery case 11.

[0024] Fig. 3 shows an exploded view of the secondary battery 20 shown in Fig. 2. An electrode body 13 is housed inside a battery case 11 of the secondary battery 20 shown in the figure, with an insulating sheet 12 interposed therebetween.

[0025] Here, the electrode body 13 has the configuration shown in Fig. 4. A positive electrode body (positive electrode) 301 and a negative electrode body (negative electrode) 302 are wound in a flat shape around a winding axis L with a separator 303 interposed therebetween. As a result, the electrode body 13 is formed with a pair of curved portions 13a, 13b (see Fig. 3) that face each other and have a substantially semicircular cross section, and a flat portion 13c (see Fig. 3) that is formed continuously between the pair of curved portions 13a, 13b.

[0026] At least a portion of the flat portion 13c of the electrode body 13, which is a metal foil exposed portion, is a positive foil exposed portion 301c and a negative foil exposed portion 302c, which are described later, bundled together to form a flat plate, forming a positive-side bundled flat portion 301d (see FIG. 3) and a negative-side bundled flat portion 302d (see FIG. 3). Note that the positive-side bundled flat portion 301d and the negative-side bundled flat portion 302d are sometimes referred to as the positive-side foil exposed portion 301c and the negative-side bundled flat portion 302c.

[0027] The positive electrode side bundling flat portion 301d and the negative electrode side bundling flat portion 302d are overlapped with the joint area 42P on one end side of the positive electrode side current collector 14P and the joint area 42N on one end side of the negative electrode side current collector 14N, respectively, and connected by ultrasonic welding.

[0028] These joint areas 42P, 42N are joined to the positive electrode side bundling flat portion 301d and the negative electrode side bundling flat portion 302d, and therefore in Figure 3 the joint areas 42P, 42N are shown by dashed lines as existing on the opposite side of the positive electrode side current collector plate 14P and the negative electrode side current collector plate 14N.

[0029] The bonding areas 42P and 42N are depicted imaginarily because they are formed by ultrasonic welding. The formation positions of these bonding areas 42P and 42N are the subject of this embodiment, and will be described later with reference to the drawings.

[0030] The electrode body 13 is inserted into the battery case 11 from one curved portion 13b side with its winding axis L direction aligned with the width direction of the battery case 1, and is positioned so that the other curved portion 13a side faces the upper opening of the battery case 11.

[0031] The other end of the positive current collector plate 14P and the other end of the negative current collector plate 14N are connected to the positive external electrode terminal 8P and the negative external electrode terminal 8N, respectively, via the battery lid 6. The positive external electrode terminal 8P and the negative external electrode terminal 8N have welded joints that are welded to a bus bar or the like (not shown). This welded joint has a rectangular parallelepiped block shape that protrudes upward from the battery lid 6, with its lower surface facing the surface of the battery lid 6 and its upper surface parallel to the battery lid 6 at a predetermined height.

[0032] A positive electrode connection portion 12P for connecting the positive electrode external electrode terminal 8P and the positive electrode side current collector plate 14P is integrally formed on the underside of the welded joint of the positive electrode side external electrode terminal 8P, and a negative electrode connection portion 12N for connecting the negative electrode side external electrode terminal 8N and the negative electrode side current collector plate 14N is integrally formed on the underside of the welded joint of the negative electrode side external electrode terminal 8N.

[0033] The positive and negative current collector plates 14P and 14N have rectangular plate-shaped fixed bases 41P and 41N that are disposed opposite the lower surface of the battery lid 6. The fixed bases 41P and 41N are formed with openings 43P and 43N, respectively, through which the positive and negative electrode connecting portions 12P and 12N formed on the positive and negative external electrode terminals 8P and 8N are inserted.

[0034] The positive electrode side current collector 14P and the negative electrode side current collector 14N are bent at the side ends of the fixed bases 41P and 41N, and extend along the wide surface of the battery case 11 toward the bottom side, and have joining areas 42P and 42P that are joined in a superimposed state facing the positive electrode side bundling flat portion 301d and the negative electrode side bundling flat portion 302d of the electrode body 13.

[0035] The positive electrode connecting portion 12P of the positive electrode side external electrode terminal 8P and the negative electrode connecting portion 12N of the negative electrode side external electrode terminal 8N have cylindrical tips that protrude from the lower surfaces of the positive electrode side external electrode terminal 8P and the negative electrode side external electrode terminal 8N, respectively, and can be inserted into the through holes 6P, 6N formed in the battery lid 6.

[0036] The positive electrode connecting portion 12P and the negative electrode connecting portion 12N penetrate the battery lid 6 via the through holes 6P and 6N, and protrude further into the battery case 11 than the fixing bases 41P and 41N of the positive electrode side current collector plate 14P and the negative electrode side current collector plate 14N via the opening holes 43P and 43N of the fixing bases 41P and 41N, with their tips crimped. In this way, the positive electrode side external electrode terminal 8P and the positive electrode side current collector plate 14P, and the negative electrode side external electrode terminal 8N and the negative electrode side current collector plate 14N are fixed integrally to the battery lid 6.

[0037] Here, a gasket 15 is interposed between the positive external electrode terminal 8P and the negative external electrode terminal 8N and the battery lid 6. Furthermore, an insulating plate 16 is interposed between the positive current collector plate 14P and the negative current collector plate 14N and the battery lid 6, and the positive external electrode terminal 8P and the negative external electrode terminal 8N, as well as the positive current collector plate 14P and the negative current collector plate 14N, are electrically insulated from the battery lid 6 by the gasket 15 and the insulating plate 16.

[0038] In addition, a liquid filling port 10 is formed in the battery lid 6, and after the electrolyte is poured into the battery case 11 through this liquid filling port 10, a sealing plug 9 is welded to this liquid filling port 10 to hermetically seal the secondary battery 20.

[0039] The battery case 11, the battery lid 6, the positive electrode side current collector 14P, and the positive electrode side external electrode terminal 8P are made of an aluminum-based material (including aluminum), and the negative electrode side current collector 14N and the negative electrode side external electrode terminal 8N are made of a copper-based material (including copper).

[0040] As described above, the positive electrode side current collector plate 14P and the negative electrode side current collector plate 14N are ultrasonically welded to the positive electrode side bundling flat plate portion 301d and the negative electrode side bundling flat plate portion 302d while being attached and fixed to the battery lid 6. Therefore, mechanical vibrations generated by the ultrasonic horn used for ultrasonic welding are transmitted to the battery lid 6 via the positive electrode side current collector plate 14P and the negative electrode side current collector plate 14N, and the mechanical vibrations acting on the battery lid 6 act as a mechanical force on the gas release valve 7.

[0041] It is conceivable that this mechanical force will damage the gas release valve 7, preventing it from performing its intended function. In this case, the secondary battery will be judged as defective, resulting in a problem of a high defect rate.

[0042] In order to solve this problem, this embodiment is characterized by a configuration in which the joint regions between the positive and negative current collector plates 14P, 14N and the positive and negative bundling flat portions 301d, 302d of the electrode body 13 are formed near the leading ends of the other ends (the ends opposite the fixed ends of the external electrode terminals) of the positive and negative current collector plates 14P, 14N. In other words, the joint regions where the current collector plate 14N and the electrode body 13 are joined are formed in an end region located away from the one side on the other side of the current collector plate 14N.

[0043] In this embodiment, the positions of the bonding regions are specified for the positive current collector plate 14P and the negative current collector plate 14N, but depending on the metal materials of the positive current collector plate 14P and the negative current collector plate 14N, it may not be necessary to specify the positions of the bonding regions. In this case, bonding may be performed at the positions of the conventional bonding regions.

[0044] According to the inventors' findings, it has been found that the negative electrode side current collector plate 14N made of a copper-based material is less affected by mechanical vibrations, and therefore there is little need to specify the formation position of the bonding area portion for the negative electrode side current collector plate 14N made of a copper-based material.

[0045] Copper-based materials have a higher specific gravity than aluminum-based materials. As a result, copper-based materials are less susceptible to vibration during ultrasonic welding, and the vibration energy is small. Therefore, mechanical vibration is not as much of a problem with copper-based materials as it is with aluminum-based materials.

[0046] Therefore, in this case, it is only necessary to specify the position of the bonding region for the positive current collector plate 14P made of an aluminum-based material. Of course, this embodiment may also be applied to the negative current collector plate 14N made of a copper-based material if it is affected by mechanical vibrations.

[0047] FIG. 5 shows the battery cover 6 in a state where the positive electrode side current collector plate 14P and the negative electrode side current collector plate 14N are separated, and FIG. 6 shows the battery cover 6 in a state where the positive electrode side current collector plate 14P and the negative electrode side current collector plate 14N are integrally attached.

[0048] 5, an insulating plate 16 corresponding to the positive external electrode terminal 8P and the negative external electrode terminal 8N is attached to the inner wall 6W (the side fixed to the battery case 11) on the inner side of the battery lid 6. A positive current collector plate 14P and a negative current collector plate 14N are attached to the inner wall 6W on the inner side of the battery lid 6 so as to sandwich the insulating plate 16 therebetween.

[0049] Then, the battery cover 6, the positive electrode side current collector plate 14P, and the negative electrode side current collector plate 14N assembled as shown in Figure 6 are placed on the positive electrode side bundling flat plate portion 301d and the negative electrode side bundling flat plate portion 302d of the electrode body 13 and set in the joining jig. This state will be described with reference to Figure 7.

[0050] Next, the configurations of the positive electrode side current collector plate 14P and the negative electrode side current collector plate 14N will be described. Here, since the positive electrode side current collector plate 14P and the negative electrode side current collector plate 14N have almost the same configuration, the following description will focus on the positive electrode side current collector plate 14P made of an aluminum-based material. However, for the negative electrode side current collector plate 14N, the "P" in the reference number will be replaced with "N."

[0051] 5 and 6 , the positive electrode side current collector 14P is formed to include a flat fixed base 41P fixed to the inner wall 6W on the inner side of the battery lid 6 with the insulating plate 16 sandwiched therebetween, and a current collector 44P extending vertically or approximately vertically from the fixed base 41P. Therefore, the positive electrode side current collector 14P extends vertically or approximately vertically with respect to the inner wall 6W on the inner side of the battery lid 6.

[0052] The current collector 44P has a sloped portion 45P formed midway, which slopes toward the inside of the storage space of the battery case 11, and a current collector main body portion 46P extending continuously from the sloped portion 45P. The current collector main body portion 46P refers to the portion from the connection with the sloped portion 45P to the tip portion 47P. As shown in FIG. 3 , the sloped portion 45P is formed for the purpose of bringing the current collector main body portion 46P closer to the positive electrode side bundling flat plate portion 301d in order to join the current collector main body portion 46P and the positive electrode side bundling flat plate portion 301d.

[0053] The current collector body 46P is an overlapping region that overlaps the positive electrode-side bundling flat plate portion 301d so as to contact the positive electrode-side bundling flat plate portion 301d, and a joint region 42P is set in part of this overlapping region. This joint region 42P is formed closer to the tip end 47P of the current collector body 46P. In other words, it is formed in an end region located away from one side on the other side of the current collector plate 14P. The end region is an area near the tip end 47 and has an area large enough to form the joint region 42P. The joint region 42P generally corresponds to the area that comes into contact with the anvil, as described below.

[0054] In this way, by positioning the joint area 42P closer to the tip 47P of the collector body 46P, the distance between the joint area 42P and the fixed base 41P in the collector 44P can be increased, i.e., the propagation distance of mechanical vibrations can be increased.

[0055] If the width and thickness of the current collector 44P are constant, the attenuation of the energy of mechanical vibration depends on the propagation distance, and the longer the propagation distance, the greater the amount of attenuation tends to be. One reason for this is that, in the region between the bonding region 42P and the fixed base 41P of the current collector 44, if the distance between the bonding region 42P and the fixed base 41P is long, the region that can move freely increases, thereby enabling the attenuation of mechanical vibration.

[0056] In other words, as the mechanical vibrations during ultrasonic welding propagate from the joining area 42P to the fixed base 41P, the vibration energy spreads over a wide area with distance, and the energy per unit area decreases, which is thought to reduce the mechanical vibrations at the fixed base 41P.

[0057] In this way, by increasing the distance between the bonding region 42P and the fixed base 41P, mechanical vibrations can be efficiently attenuated. Therefore, even if mechanical vibrations generated by the ultrasonic horn used for ultrasonic welding are transmitted to the battery lid 6 via the current collector 44P, the mechanical vibrations are attenuated and therefore the mechanical vibrations acting on the battery lid 6 do not damage the gas release valve 7. The positional definition, area, etc. of the bonding region 42P will be explained using FIG. 8.

[0058] 7, ultrasonic welding for joining the positive electrode side current collector plate 14P and the positive electrode side bundled flat plate portion 301d of the electrode body 13 will be described. The same applies to the negative electrode side current collector plate 14N and the negative electrode foil exposed portion 302c of the electrode body 13.

[0059] In ultrasonic welding, with the battery cover 6 and the positive electrode side current collector 14P integrated as shown in Figure 6, the anvil 51 of the ultrasonic welding device is brought into contact with the positive electrode side current collector 14P so as to sandwich the positive electrode side current collector 14P and the positive electrode side bundling flat plate portion 301d, and the ultrasonic horn 50 is brought into contact with the positive electrode side bundling flat plate portion 301d.

[0060] Then, the anvil 51 and the ultrasonic horn 50 press the positive electrode side current collector 14P and the positive electrode side bundling flat portion 301d together, and then the ultrasonic horn 50 is vibrated to join the positive electrode side current collector 14P and the positive electrode foil exposed portion 301c of the electrode body 13.

[0061] Fig. 7 is a schematic diagram showing the process of joining the current collector plate 14P to the electrode body 13 shown in Fig. 3. Note that Fig. 7 explains the process on the positive electrode side, but the process on the negative electrode side is similar.

[0062] As shown in Figure 7, the current collector body portion 46P of the positive side current collector plate 14P is placed on one surface 301df of the positive side bundled flat portion 301d, which is formed by bundling the positive foil exposed portions 301c of the electrode body 13 into a flat plate shape, and with the flat portions of the positive foil exposed portions 301c of the electrode body 13 and the current collector body portion 46P of the positive side current collector plate 4A abutting against each other, they are pressed in the direction of the outline arrow to be joined.

[0063] Specifically, based on the position where the flat surfaces of the positive electrode-side bundling flat plate portion 301d of the electrode body 13 and the current collector body 46P of the positive electrode-side current collector plate 14P abut against each other, the ultrasonic horn 50 is disposed on the opposite side of the positive electrode-side bundling flat plate portion 301d, and the anvil 51 is disposed on the current collector body 46P side of the positive electrode-side current collector plate 14P. Here, at least the cross-sectional shape of the anvil 51 perpendicular to the pressing direction of the anvil 51 is formed into a rectangular shape.

[0064] The ultrasonic horn 50 and the anvil 51 press and clamp the positive electrode side bundling flat plate portion 301d and the current collector body 46P of the electrode body 13 in the direction of the outline arrow, and in this state, the ultrasonic horn 51 is mechanically vibrated. Frictional heat generated by this mechanical vibration bonds the positive electrode side bundling flat plate portion 301d and the current collector body 46P to form the bonding region 42P. As described above, the bonding region 42P is formed corresponding to the area where the anvil 51 contacts the current collector body 46P.

[0065] In this embodiment, the joining area 42P is formed closer to the tip 47P of the current collector body 46P, so the anvil 51 and the ultrasonic horn 50 are positioned closer to the tip 47P of the current collector body 46P.

[0066] That is, since friction welding is performed in the region where the pressing force between the anvil 51 and the ultrasonic horn 50 is large, it is desirable to position the anvil 51 as close as possible to the tip 47P of the current collector body 46P. As explained above, this is because increasing the distance between the bonding region 42P and the fixed base 41P efficiently attenuates mechanical vibrations.

[0067] Here, the joining region 42P has a shape similar to the shape (contact shape) of the anvil 51 that comes into contact with the current collector body 46P when the anvil 51 is pressed against the current collector body 46P. In this case, the shape of the joining region 42P may be larger or smaller than the contact shape of the anvil, but in either case, the shape is similar.

[0068] Therefore, the shape of the joining region 42P after joining can be confirmed by observing the joining marks of the anvil 51 formed on the surface of the current collector body 46P by the pressure of the anvil 51. The joining marks are uneven pressing marks formed by the contact / pressure of the anvil 51 causing plastic deformation of the surface of the current collector body 46P.

[0069] Furthermore, by observing the bonding marks, it is possible to determine the position where the anvil 51 made contact, that is, the position of the bonding region 42P on the current collector main body 46P can be inferred.

[0070] Furthermore, because mechanical vibrations are transmitted to the battery lid 6 by the positive electrode side current collector plate 14P, it is desirable that the current collector body 46P be pressed by the anvil 51. If the current collector body 46P were pressed by the ultrasonic horn 50, the mechanical vibrations of the ultrasonic horn 50 would directly act on the current collector body 46P, which is not desirable.

[0071] Next, the configuration of bringing the joint area 42P closer to the tip 47P of the current collector body 46P, which is a feature of this embodiment, will be described using the positive current collector 14P shown in Fig. 8. Here, Fig. 8 shows only the positive current collector 14P after the positive current collector 14P and the electrode body 13 have been joined. For this reason, a welding mark 52P from the anvil 51 used in the welding operation is formed on the tip 47P side of the current collector body 46P.

[0072] As described above, the main purpose of this embodiment is to attenuate mechanical vibration energy by increasing the distance between the joint region 42P and the fixed base 41P.

[0073] Therefore, it is important that the bonding area 42P formed on the current collector body 46P is formed close to the tip 47P on the other side (opposite the fixed base) of the current collector body 46P. In this case, the formation position of the bonding area 42P, in other words, the position where the amber 51 contacts the current collector body 46P, is determined based on the concept described below.

[0074] First, the area of ​​the joining region 42P that can obtain the joining force required for the design is determined, and the tip shape of the anvil 51 corresponding to this area is determined. For example, as shown in Figure 7, the cross-sectional shape of the anvil 51 perpendicular to the pressing direction of the anvil 51 is determined to be rectangular. This is because the current collector body 46P is shaped like a long, thin strip, and the tip shape of the anvil 51 is determined to match this shape.

[0075] Next, ultrasonic welding is performed using this anvil 51. In this case, the positive electrode side current collector plate 14P and the electrode body 13 are overlapped and joined as shown in Fig. 7, but as described above, it is necessary to increase the distance between the joining region 42P and the fixed base 41P in order to attenuate mechanical vibrations.

[0076] 7, the side wall 51R of the anvil 51 opposite to the side wall 51F facing the fixed base 41P is disposed close to the tip 47P of the current collecting body 46P. In this case, the side wall 51R of the anvil 51 is disposed so as not to extend beyond the tip 47P. The distance between the tip 47P and the side wall 51R of the anvil 51 is set to a length allowed by design.

[0077] Here, the positional relationship between the anvil 51 and the ultrasonic horn 50 is such that, in order to efficiently transmit the mechanical vibrations of the ultrasonic horn 50, the contact portion of the anvil 51 with the current collector body portion 46P overlaps the contact portion with the positive electrode side bundling flat plate portion 301d of the ultrasonic horn 50. In other words, when the bonding mark 52P is projected in the direction of the bonding mark formed by the ultrasonic horn 50, the two bonding marks overlap.

[0078] Furthermore, the side wall 50R of the ultrasonic horn 50 is positioned beyond the side wall 51R of the anvil 51 toward the tip 47P. This allows for efficient transmission of mechanical vibrations to the anvil 51. The side wall 50R of the ultrasonic horn 50 and the side wall 51R of the anvil 51 can also be positioned on the same plane (i.e., flush) when viewed in the direction of pressure (indicated by the white arrow) relative to each other. In either case, the ultrasonic horn 50 is also positioned closer to the tip 47P of the current collector body 46P. This allows for efficient transmission of mechanical vibrations to the anvil 51.

[0079] In this embodiment, the key point is that the distance between the joint area 42P and the fixed base 41P should be set to a length that can attenuate mechanical vibrations to the extent that the gas exhaust valve 7 is not damaged, and for this purpose, the side wall 51R of the anvil 51 is positioned close to the tip 47P of the collector body 46P.

[0080] 8, an example of a bonding mark 52P is shown when the anvil 51 is pressed against the current collector body 46P in the direction of the outline arrow. In the following description, the bonding mark 52P and the bonding region 42P correspond to each other in position, and therefore will be described as being substantially synonymous.

[0081] When the total length of the current collecting body 46P (the length from the connection point with the inclined portion 45P of the current collecting body 46P to the tip 47P) is "L", the joint mark 52P is formed close to the tip 47P, within a range of "L / 2" as viewed from the tip 47P, which is obtained by dividing the current collecting body 46P into two equal halves, so as to be closer to the tip 47P.

[0082] Therefore, the length from the side opposite to the side of the joining area portion 42P facing the tip portion 47P to the fixed base 41P is approximately equal to or greater than "L / 2" plus the length of the inclined portion 45P and the connection portion 48P connecting the fixed base 41P and the inclined portion 45P.

[0083] Here, the above-mentioned "close to the tip 47P" means that the rectangular weld mark 52P, in other words, the side of the welded region 42P facing the tip 47P, is close to the tip 47P, on the premise that it does not extend beyond the tip 47P. Of course, the distance between the side of the welded region 42P facing the tip 47P and the tip 47P is a length required for design.

[0084] However, if a large area of ​​the joining region 42P is required, it is expected that the length of the joining mark 52P from the tip 47P side will exceed "L / 2", as shown by the joining mark 52P indicated by the dashed line.

[0085] Even in this case, since the anvil 51 is disposed closer to the tip end 47P, most of the area of ​​the weld mark 52P is within the range of "L / 2" from the tip end 47P. For example, 50% or more of the weld mark 52P is within the range of "L / 2" from the tip end 47P.

[0086] This allows the distance between the bonding region 42P and the fixed base 41P to be as long as possible. Here, the distance between the bonding region 42P and the fixed base 41P is the distance between the fixed base 41P and the farthest side of the bonding region 42P as viewed from the tip 47P. In other words, it is the distance from the side of the rectangular bonding region 42P that is opposite to the side facing the tip 47P.

[0087] This allows the propagation distance of the vibration to be as long as possible, and the mechanical vibration to be effectively attenuated. As a result, even if the mechanical vibration generated by the ultrasonic horn 50 for ultrasonic welding is propagated to the battery cover 6 via the current collector 44P, the mechanical vibration is attenuated, and therefore the mechanical vibration acting on the battery cover 6 does not damage the gas release valve 7.

[0088] The above explanation shows that mechanical vibrations in the current collector 44P can be damped by making the length between the joint region 42P and the fixed base 41P as long as possible.

[0089] In response to this, by reducing the contact area of ​​the anvil 51 with the collector body 46P, it is possible to reduce the energy of the mechanical vibration input to the collector 44P and thereby reduce the mechanical force acting on the gas exhaust valve 7.

[0090] 7, the area (Sa) where the anvil 51 contacts the current collector body 46P is set smaller than the area (Sh) where the ultrasonic horn 50 contacts the positive electrode-side bundling flat plate portion 301d. According to the inventors' findings, when the ratio Sa / Sh is set to less than 1.0 (Sa / Sh<1.0), the mechanical vibration energy input to the current collector 44P can be effectively reduced. The areas (Sa) and (Sh) can also be considered to be the areas of the bonding marks formed by the anvil 51 and the ultrasonic horn 50.

[0091] Furthermore, if the contact area of ​​the anvil 51 can be reduced, this can indirectly contribute to increasing the distance between the joining region 42P and the fixed base 41P.

[0092] Next, a modified example of the positive current collector plate 14P will be described. In this modified example, the connection portion 48P connecting the inclined portion 45P and the fixed base 41P in the positive current collector plate 14P shown in Fig. 8 is replaced with a buffer connection portion 49P. Note that the buffer connection portion has a "flexible structure," and the configuration other than the buffer connection portion 49P is the same as the configuration in Fig. 8, so a description thereof will be omitted.

[0093] 9, a buffer connection portion 49P is integrally formed on the positive current collector plate 14P as a connection portion connecting the inclined portion 45P and the fixed base 41P. This buffer connection portion 49P extends convexly in the same direction as the inclined portion 45P. That is, the cross-sectional shape in a direction perpendicular to the flat portion 53P on which the joining mark 52P of the current collector body portion 46P is formed is arc-shaped. In this case, it is formed in a semicircular shape. Furthermore, the width and thickness of the buffer connection portion 49P are formed to be the same as those of the inclined portion 45P and the current collector body portion 46P.

[0094] The arc-shaped buffer connection portion 49P can increase the distance between the fixed base portion 41P and the bonding area portion 42P, thereby damping mechanical vibrations for the reasons described above. More importantly, the buffer connection portion 49P also has elasticity, which allows the current collector 44P to move more freely, thereby effectively damping mechanical vibrations.

[0095] In this manner, in this modification, the buffer connection portion 49P is formed between the fixed base portion 41P and the inclined portion 45P, so that mechanical vibrations can be further suppressed.

[0096] As described above, the present invention provides a secondary battery having an electrode body including a positive electrode material and a negative electrode material, a battery container that houses the electrode body, a battery lid that seals the battery container, a current collector plate that is disposed inside the battery container and joined to the electrode body by ultrasonic welding, an external electrode terminal that is provided on the outer surface of the battery lid and connected to the current collector plate, and a gas release valve that is provided on the battery lid, wherein one side of the current collector plate is electrically connected to the external electrode terminal and fixed to the battery lid, the other side of the current collector plate is joined to the electrode body, and the joining region where the current collector plate and the electrode body are joined is formed toward the tip of the other side of the current collector plate.

[0097] This allows the propagation distance from the connection area of ​​the current collector plate to the fixed position on the battery lid to be long, and the mechanical force caused by the mechanical vibrations of ultrasonic welding acting on the battery lid is weakened or absorbed by the long propagation distance of the current collector plate, thereby suppressing damage to the gas release valve and reducing the defect rate.

[0098] The present invention is not limited to the above-described embodiments, but includes various modifications. The above-described embodiments have been described in detail to clearly explain the present invention, and the present invention is not necessarily limited to those including all of the described configurations. Furthermore, it is possible to replace part of the configuration of one embodiment with the configuration of another embodiment, and it is also possible to add the configuration of another embodiment to the configuration of one embodiment. It is also possible to add, delete, or replace other configurations with respect to the configuration of each embodiment.

[0099] 6...battery lid, 6W...inner wall, 7...gas release valve, 8P...positive electrode side external electrode terminal, 8N...negative electrode side external electrode terminal, 9...sealing plug, 10...filling port, 11...battery case, 13...electrode body, 14P...positive electrode side current collector plate, 14N...negative electrode side current collector plate, 41P, 41N...fixed base, 42P, 42N...connection area portion, 44P, 44N...current collector, 45P, 45N...inclined portion, 46P, 46N...current collector main body portion, 47P, 47N...tip portion, 48P...connection portion, 50...ultrasonic horn, 51...anvil.

Claims

1. An electrode body comprising a positive electrode material and a negative electrode material, A battery container for housing the electrode body, and a battery cover for sealing the battery container, A current collector plate is placed inside the aforementioned battery container, A secondary battery having external electrode terminals provided on the outer surface of the battery cover and a gas discharge valve provided on the battery cover, One side of the current collector plate is electrically connected to the external electrode terminal and fixed to the battery cover, and the other side of the current collector plate is joined to the electrode body. The joining region where the current collector plate and the electrode body are joined is formed in the end region of the tip portion located on the other side of the current collector plate, away from the one side of the current collector plate. A secondary battery characterized by the following features.

2. In the secondary battery according to claim 1, The aforementioned joining region is formed at the position where the anvil for ultrasonic welding makes contact. A secondary battery characterized by the following features.

3. In the secondary battery according to claim 1, The current collector plate has a fixed base provided on one side of the current collector plate and a current collector body extending away from the fixed base on the other side of the current collector plate. The current collector comprises a current collector body portion on which the end region is provided, The aforementioned joining region is formed within a range that does not exceed the end region of the current collector body. A secondary battery characterized by the following features.

4. In the secondary battery described in claim 3, When the current collector body is divided equally into two parts in the direction toward the tip of the current collector plate, the joining region is formed in the two divided regions on the tip side. A secondary battery characterized by the following features.

5. In the secondary battery described in claim 3, When the current collector body is divided equally into two parts in the direction toward the tip of the current collector plate, more than 50% of the joint area is formed in the two divided areas on the tip side. A secondary battery characterized by the following features.

6. In the secondary battery described in claim 2, When the contact area of ​​the anvil that is pressed against the current collector plate for ultrasonic welding is "Sa", and the contact area of ​​the ultrasonic horn that is pressed against the electrode body is "Sh", the relationship "Sa / Sh < 1.0" exists. A secondary battery characterized by the following features.

7. In the secondary battery according to claim 6, The position to which the ultrasonic horn for performing the ultrasonic welding makes contact is set in the end region on the other side of the current collector plate. A secondary battery characterized by the following features.

8. In the secondary battery according to claim 7, The joint mark formed by the anvil and the joint mark formed by the ultrasonic horn overlap when projected toward each other in the direction in which the anvil and the ultrasonic horn are pressed. A secondary battery characterized by the following features.

9. In the secondary battery described in claim 3, Between the fixing base, which is fixed to the battery cover, and the current collector body, a buffer connection portion is formed to weaken or absorb mechanical vibrations caused by ultrasonic welding. A secondary battery characterized by the following features.

10. In the secondary battery according to claim 9, The buffer connection portion is formed in a shape that provides elasticity to reduce or absorb the mechanical vibrations. A secondary battery characterized by the following features.

11. In the secondary battery according to claim 10, The buffer connection portion is formed in an arc shape that is bent and protrudes in a direction perpendicular to the flat surface of the current collector body. A secondary battery characterized by the following features.

12. In the secondary battery according to any one of claims 1 to 11, The current collector plate is a positive electrode current collector plate made from an aluminum-based material. A secondary battery characterized by the following features.

13. A battery pack is constructed by stacking multiple secondary batteries, each having an electrode body equipped with a positive electrode material and a negative electrode material, a battery container housing the electrode body, a battery cover sealing the battery container, a current collector plate disposed inside the battery container and joined to the electrode body by ultrasonic welding, an external electrode terminal provided on the outer surface of the battery cover and connected to the current collector plate, and a gas discharge valve provided on the battery cover. The secondary battery used is the secondary battery described in any one of claims 1 to 11. A battery pack characterized by the following features.

14. A method for joining a current collector plate of a secondary battery, comprising an electrode body having a positive electrode material and a negative electrode material, a battery container housing the electrode body, a battery cover sealing the battery container, a current collector plate disposed inside the battery container and joined to the electrode body by ultrasonic welding, an external electrode terminal provided on the outer surface of the battery cover and connected to the current collector plate, and a gas discharge valve provided on the battery cover, The ultrasonic welding is performed with the current collector plate and the battery cover fixed together, using an anvil that presses the current collector plate and an ultrasonic horn that presses the electrode body. The anvil is positioned towards the other end of the current collector plate opposite to the side fixed to the battery cover, and the ultrasonic horn is positioned corresponding to the position of the anvil. In this state, the ultrasonic horn is mechanically vibrated to form a junction area between the current collector plate and the electrode body at the position where the anvil is located. A method for joining current collector plates of a secondary battery, characterized by the features described above.

15. In the method for joining current collector plates of a secondary battery according to claim 14, The current collector plate comprises a fixed base that is fixed to the battery cover and a current collector extending from the fixed base to the tip, the current collector having a current collector body that extends toward the tip and contacts the electrode body, When the current collector body is divided equally into two parts in the direction toward the tip of the current collector plate, the anvil is positioned such that the joining region is formed in the two divided regions on the tip side. A method for joining current collector plates of a secondary battery, characterized by the features described above.

16. In the method for joining current collector plates of a secondary battery according to claim 14, The current collector plate comprises a fixed base that is fixed to the battery cover and a current collector extending from the fixed base to the tip, the current collector having a current collector body that extends toward the tip and contacts the electrode body, When the current collector body is divided equally into two parts in the direction toward the tip of the current collector plate, the anvil is positioned such that 50% or more of the joining region is formed in the two divided regions on the tip side. A method for joining current collector plates of a secondary battery, characterized by the features described above.