Secondary battery and battery pack

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 joining of the current collector and a metal foil exposure section; and a battery pack　The secondary battery includes: an electrode body 13 that comprises a positive electrode material and a negative electrode material; a battery container 11 that accommodates the electrode body 13; a battery lid 6 that seals the battery container; a collector plate 14 that is disposed inside of the battery container 11 and is joined to the electrode body 13 by using ultrasonic welding; an external electrode terminal 8 that is provided on the outer surface of the battery lid 6 and is connected to the collector plate 14; and a gas discharge valve 9 that is provided in the battery lid 6. One side of the collector plate 14 is fixed to the battery lid 6 with a fixing base part 41 therebetween. The other side of the collector plate 14 is joined to the electrode body 13 with a joint region part 42 therebetween. A buffer connection part 49 for weakening or absorbing mechanical force resulting from mechanical vibration due to ultrasonic welding is formed between the fixing base part 41 and the joint region part 42.

Description

Secondary batteries and battery packs

[0001] The present invention relates to a secondary battery and a battery pack incorporating such secondary batteries.

[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 can be considered for welding the exposed metal foil portion and the current collecting plate, the most common method is to join the exposed metal foil portion and the current collecting plate by ultrasonic welding. For example, Patent Document 1 discloses a method in which the exposed metal foil portion and the current collecting plate are clamped between an ultrasonic horn and an anvil to perform solid-state welding.

[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 joining device and brought into contact with the current collector plate, and an ultrasonic horn is brought into contact with the exposed metal foil portion, so that the current collector plate and the exposed metal foil portion are pressed together by the anvil and ultrasonic horn, and the ultrasonic horn is then vibrated to solid-state join 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 bonded to the exposed metal foil portion. Therefore, mechanical vibrations generated by the ultrasonic horn used for ultrasonic bonding are transmitted to the battery lid via the current collector plate, and 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 that can suppress 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, and a battery pack that combines this secondary battery.

[0011] 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 exhaust valve that is provided on the battery lid, wherein one side of the current collector plate is fixed to the battery lid via a fixed base, and the other side of the current collector plate is joined to the electrode body via a bonding area, and a buffer connection is formed between the fixed base and the bonding area.

[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] According to the present invention, a buffer connection is formed between the joining area of ​​the current collector plate and the fixed base, so that the mechanical force caused by the mechanical vibrations of ultrasonic welding acting on the battery lid is weakened or absorbed by the buffer connection, thereby suppressing damage to the gas release valve and reducing the defect rate.

[0014] 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 an electrode body shown in FIG. 4 is an external perspective view of a current collector plate according to a first embodiment of the present invention before the battery lid is assembled; FIG. 4 is an external perspective view of a current collector plate according to a first embodiment of the present invention after the battery lid is assembled; FIG. 5 is an explanatory diagram of ultrasonic welding for contacting and pressing a current collector plate and an electrode body to join them; FIG. 6 is an external perspective view of a current collector plate according to a first embodiment of the present invention, seen from the side where an anvil comes into contact; FIG. 7 is an external perspective view of a current collector plate according to a first embodiment of the present invention, seen from the side where a bonding area portion is formed; FIG. 8 is an external perspective view of a current collector plate according to a second embodiment of the present invention before the battery lid is assembled; FIG. 9 is an external perspective view of a current collector plate according to a second embodiment of the present invention after the battery lid is assembled; FIG. 10 is an external perspective view of a current collector plate according to a second embodiment of the present invention, seen from the side where an anvil comes into contact; FIG. 11 is an external perspective view of a current collector plate according to a second embodiment of the present invention, seen from the side where a bonding area portion is formed; FIG. 12 is an external perspective view of a current collector plate according to a third embodiment of the present invention before the battery lid is assembled; 20 is an external perspective view of a current collecting plate according to a third embodiment of the present invention after assembly with a battery lid. FIG. 21 is an external perspective view of a current collecting plate according to a third embodiment of the present invention, seen from the side where an anvil comes into contact. FIG. 22 is an external perspective view of a current collecting plate according to a third embodiment of the present invention, seen from the side where a bonding area portion is formed. FIG. 23 is an external perspective view of a current collecting plate according to a fourth embodiment of the present invention before assembly with a battery lid. FIG. 24 is an external perspective view of a current collecting plate according to a fourth embodiment of the present invention after assembly with a battery lid. FIG. 25 is an external perspective view of a current collecting plate according to a fourth embodiment of the present invention, seen from the side where a bonding area portion is formed. FIG. 26 is a side view of the current collecting plate shown in FIG. 20, seen from the side along the longitudinal direction.

[0015] 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.

[0016] 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 20 is the Y-axis direction, and the height direction of the secondary batteries 20 is the Z-axis direction.

[0017] 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.

[0018] The end plates 4 may be omitted. In this case, the secondary battery 20 is held by the side plates 5.

[0019] A battery lid 6 is attached to the upper side of the secondary battery 20, and a positive external electrode terminal 8P and a negative external electrode terminal 8N, which are external electrode terminals, 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 or exceeds a predetermined value. The sealing plug 9 also has the function of sealing the secondary battery 20 after a liquid electrolyte has been injected therein.

[0020] Fig. 2 shows the external 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.

[0021] The battery cover 6 is provided with a positive external electrode terminal 8P and a negative external electrode terminal 8N, and the electrode body 13 (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.

[0022] 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, allowing gas to be released from the battery container, thereby 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.

[0023] Fig. 3 shows an exploded view of the secondary battery 20 shown in Fig. 2. In Fig. 3, "P" attached to the reference numerals indicates the positive electrode side, and "N" indicates the negative electrode side.

[0024] An electrode body 13 is housed inside a battery case 11 of the illustrated secondary battery 20 via an insulating sheet 12. The electrode body 13 has the configuration shown in FIG.

[0025] 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-side bundling flat portion 301d and the negative-side bundling flat portion 302d are respectively superposed on a joining area 42P at one end of the positive-side current collector plate 14P and a joining area 42N at one end of the negative-side current collector plate 14N, and are joined by ultrasonic welding. The joining areas 42P and 42N will be described later.

[0028] The joining regions 42P, 42N are joined to the positive electrode side bundling flat plate portion 301d and the negative electrode side bundling flat plate portion 302d, so that in Fig. 3 the joining regions 42P, 42N are present on the opposite surfaces of the positive electrode side current collector plate 14P and the negative electrode side current collector plate 14N. For this reason, the lead lines are shown as dashed lines.

[0029] 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 11, and is positioned so that the other curved portion 13a side faces the upper opening side of the battery case 11.

[0030] 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.

[0031] 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.

[0032] The positive and negative current collector plates 14P, 14N have rectangular plate-shaped fixed bases 41P, 41N that are disposed opposite the lower surface of the wall of the battery lid 6. The fixed bases 41P, 41N are formed with openings 43P, 43N, through which the positive and negative electrode connecting portions 12P, 12N formed on the positive and negative external electrode terminals 8P, 8N are inserted, respectively.

[0033] 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, extend along the wide surface of the battery case 11 toward the bottom side, and have joining areas 42P and 42N 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.

[0034] Although not clearly shown here, a buffer connection 49P, which is the subject of this embodiment, is formed between the fixed base 41P and the joint area 42P of the positive current collector plate 14P. The buffer connection 49P is a mechanism that weakens or absorbs mechanical forces caused by mechanical vibrations due to ultrasonic welding, and has a "flexible structure." A similar buffer connection can also be formed on the negative current collector plate 14N. This buffer connection 49P will be explained again using the drawings.

[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 attached and fixed to the battery lid 6 (however, the positive electrode side external electrode terminal 8P and the negative electrode side external electrode terminal 8N are not attached), and are ultrasonically joined to the positive electrode side bundling flat plate portion 301d and the negative electrode side bundling flat plate portion 302d.

[0041] Therefore, mechanical vibrations generated by the ultrasonic horn used for ultrasonic bonding are transmitted to the battery lid 6 via the positive electrode side current collector plate 14P, and the mechanical vibrations acting on the battery lid 6 act as mechanical forces on the gas release valve 7. According to the findings of the inventors, since the negative electrode side current collector plate 14N is made of a copper-based material, no significant vibration propagation was observed.

[0042] Therefore, it is conceivable that the gas release valve 7 may be damaged and unable to perform its intended function. In this case, the secondary battery will be judged as defective, resulting in a problem of a high defect rate.

[0043] Hereinafter, the configuration of the current collector plate, which is the subject of the present invention, will be described with reference to the drawings in several embodiments.

[0044] In order to solve the problems described above, in this embodiment, as shown in Figure 5, the other end of the current collector plate 14P is joined to the electrode body 13 (see Figure 3) via the joining area 42P, and a buffer connection part 49PA is formed between the fixed base 41P and the joining area 42P, which weakens or absorbs the mechanical force acting on the gas release valve 7 of the battery lid based on the mechanical vibration caused by ultrasonic welding.

[0045] In this embodiment, the buffer connections 49P and 49N may be formed on the positive current collector plate 14P and the negative current collector plate 14N, but depending on the metal material of the positive current collector plate 14P and the negative current collector plate 14N, it may not be necessary to form the buffer connections 49P and 49N. In this case, a conventional current collector plate configuration may be used.

[0046] According to the inventors' findings, it has been found that the negative electrode side current collector plate 14N made of a copper-based material in this embodiment is less affected by mechanical vibrations, and therefore there is little need to form a buffer connection portion 49N on the negative electrode side current collector plate 14N made of a copper-based material.

[0047] 3, the buffer connection 49PA described above can be formed on the positive current collector 14P made of an aluminum-based material, and the following description will focus on an embodiment in which the buffer connection 49PA is formed on the positive current collector 14P. Of course, if necessary, the buffer connection 49NA may also be formed on the negative current collector 14N.

[0048] A first embodiment of the present invention is shown in Figures 5 to 8. This first embodiment is characterized in that the buffer connection portion 49PA is formed in an arc shape so as to have elasticity.

[0049] 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.

[0050] 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.

[0051] 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 Fig. 6 are superimposed 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, set in a joining jig, and ultrasonically welded. This state will be described with reference to Fig. 7.

[0052] 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 read as "N." Furthermore, the negative electrode side current collector plate 14N does not have a buffer connection portion formed thereon.

[0053] 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.

[0054] The current collector 44P has a sloped portion 45P formed midway that extends at an angle toward the inside of the storage space of the battery case 11, and a current collector main body portion 46P is further formed that extends continuously from this sloped portion 45P.

[0055] A buffer connection portion 49PA is formed between the inclined portion 45P and the fixed base 41P. Therefore, when viewed from at least the tip end 47P side, the positive electrode side current collecting plate 14P is formed by the current collecting body portion 46P, the inclined portion 45P, the buffer connection portion 49PA, and the fixed base 41P.

[0056] The current collector body 46P, inclined portion 45P, buffer connection portion 49PA, and fixed base 41P are formed by punching a flat aluminum-based material and bending it into a predetermined shape. The negative current collector 14N is provided with a flat connection portion 48N instead of the buffer connection portion 49PA. This is because, as mentioned above, mechanical vibrations are not a significant problem when using copper-based materials.

[0057] Here, as shown in Figure 3, the inclined portion 45P is formed for the purpose of bringing the current collector body portion 46P closer to the positive electrode side bundling flat portion 301d in order to join the current collector body portion 46P and the positive electrode side bundling flat portion 301d.

[0058] The current collector body 46P is an overlapping region that is overlapped so as to come into contact with the positive electrode-side bundling flat plate portion 301d, and a joint region 42P is set within the overlapping region. This joint region 42P is formed up to the vicinity of the tip end 47P of the current collector body 46P.

[0059] 7, ultrasonic welding for joining the positive current collector plate 14P and the positive-side bundling flat portion 301d of the electrode body 13 will be briefly described. The same applies to the negative current collector plate 14N and the negative-side bundling flat portion 302d of the electrode body 13.

[0060] In ultrasonic welding, with the battery cover 6 and the positive electrode side current collector 14P integrated as shown in FIG. 6, the anvil 51 of the ultrasonic joining 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.

[0061] 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 mechanically vibrated to join the positive electrode side current collector 14P and the positive electrode side bundling flat portion 301d of the electrode body 13.

[0062] 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.

[0063] As shown in FIG. 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 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 14P are pressed in the direction of the outline arrow with their respective flat portions abutting against each other and joined together.

[0064] Specifically, based on the position where the flat portions of the positive electrode side bundling flat plate portion 301d of the electrode body 13 and the collector body portion 46P of the positive electrode side current collector plate 14P abut against each other, an ultrasonic horn 50 is placed on the opposite side of the positive electrode side bundling flat plate portion 301d, and an anvil 51 is placed on the collector body portion 46P side of the positive electrode side current collector plate 14P.

[0065] Then, 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, mechanically vibrate the ultrasonic horn 50. Frictional heat generated by this mechanical vibration bonds the positive electrode side bundling flat plate portion 301d and the current collector body 46P together to form the bonding region 42P.

[0066] Next, the specific configuration of the positive electrode side current collector 14P will be described with reference to Figures 8 and 9. Figure 8 shows the appearance of the positive electrode side current collector 14P as seen from the side where the anvil comes into contact, and Figure 9 shows the appearance of the positive electrode side current collector 14P as seen from the side where the bonding region 42P is formed.

[0067] 8 and 9, the positive electrode side current collector 14P is formed by punching a flat plate made of an aluminum-based material into a predetermined shape and then bending the punched flat plate into a predetermined shape, thereby forming the positive electrode side current collector 14P having the form shown in FIGS.

[0068] A current collector 44P is formed on the side of the flat fixed base 41P, bent in a direction perpendicular to the plane of the fixed base 41P. The current collector 44P has a generally elongated rectangular (strip-like) shape with a predetermined width and thickness, and is integrally formed with a buffer connection portion 49PA, an inclined portion 45P, and a current collector main body portion 46P in this order as seen from the fixed base 41P up to the tip portion 47P.

[0069] As can be seen from Figure 9, the inclined portion 45P and the current collector body portion 46P each have a continuously formed flat surface, and further, the inclined portion 45P is formed with a slope to bring the current collector body portion 46P closer to the positive electrode side bundling flat plate portion 301d of the electrode body 13.

[0070] 8, the current collector body 46P has, on one surface, a flat portion 46Pf with which an anvil 51 used for ultrasonic welding comes into contact, and, as shown in Fig. 9, on the other surface, a flat portion 46Pr that is joined to the positive electrode-side bundling flat portion 301d of the electrode body 13. After ultrasonic welding is performed, a joining mark 52P caused by the anvil is formed on the flat portion 46Pf, and a joining region 42P is formed on the flat portion 46Pr.

[0071] As described above, the inclined portion 45P formed continuously with the current collector body portion 46P is formed to bring the current collector body portion 46P closer to the positive electrode side bundling flat plate portion 301d, making it easier to join the current collector body portion 46P and the positive electrode side bundling flat plate portion 301d. Note that if the current collector body portion 46P and the positive electrode side bundling flat plate portion 301d can be joined without this inclined portion 45P, the inclined portion 45P can be omitted.

[0072] A buffer connection portion 49PA is integrally formed on the positive current collector plate 14P as a connection portion connecting the inclined portion 45P and the fixed base 41P. Here, the buffer connection portion 49PA has the function of weakening or absorbing the mechanical force caused by the mechanical vibrations due to ultrasonic welding, and is formed from a protrusion that extends in the inclined direction of the inclined portion 45P.

[0073] That is, the cross section of the current collecting body 46P in a direction perpendicular to the flat surface 46Pf on which the joining mark 52P is formed is formed in an arc shape, in this case a semicircular shape. Note that the buffer connection portion 49PA does not extend beyond the position of the current collecting body 46P in the direction perpendicular to the flat surface 46Pf, but exists within the space up to the position of the current collecting body 46P.

[0074] In other words, the protruding portion, which is the arc-shaped portion constituting the buffer connection portion 49PA, is formed so that the tip of the protruding portion does not extend beyond the current collecting body portion 46P that is located in the inclined direction of the inclined portion 45P. This allows the buffer connection portion 49PA to be accommodated efficiently. Also, in the embodiment, the width and thickness of the buffer connection portion 49PA are formed to be the same as those of the inclined portion 45P and the current collecting body portion 46P, but the width of the buffer connection portion 49PA may be relatively narrower than the widths of the inclined portion 45P and the current collecting body portion 46P, and the thickness of the buffer connection portion 49PA may be relatively thinner than the thicknesses of the inclined portion 45P and the current collecting body portion 46P.

[0075] The arc-shaped buffer connection 49PA can increase the vibration propagation distance between the fixed base 41P and the joint area 42P compared to the flat connection 48N of the negative current collector 14N, thereby attenuating mechanical vibration. More importantly, the arc-shaped buffer connection 49PA also has elasticity, which allows the current collector 44P to move more freely, thereby effectively attenuating mechanical vibration.

[0076] In this way, in the positive electrode current collector plate 14P of this embodiment, the elastic buffer connection portion 49PA is formed between the fixed base 41P and the inclined portion 45P, so that mechanical vibrations can be effectively suppressed or absorbed. Therefore, the gas release valve is not damaged by mechanical force, and the defective rate of secondary batteries can be kept low.

[0077] In the above-described embodiment, a buffer connection portion 49PA is formed between the fixed base portion 41P and the inclined portion 45P, but the basic idea is that it is sufficient if a buffer connection portion 49PA is formed between the fixed base portion 41P and the bonding area portion 42P.

[0078] In addition, in this embodiment, the buffer connection portion 49PA has an arc-shaped (here, semicircular) cross-sectional shape in a direction perpendicular to the flat portion 46Pf on which the joining mark 52P of the current collecting body portion 46P is formed, but this is not limited to this, and the cross-sectional shape may be triangular or trapezoidal, and the key is that it is sufficient that the protrusion portion extends so as to protrude toward the inclination direction of the inclined portion 45P.

[0079] In this way, the buffer connection portion 49PA is located between the fixed base 41P and the bonding area portion 42P, and has elasticity in the connection direction between the fixed base 41P and the bonding area portion 42P, so that it is formed in a shape that can weaken or absorb mechanical vibrations during ultrasonic bonding between the current collector 44P and the fixed base 41P.

[0080] Next, a second embodiment of the present invention will be described with reference to Figures 10 to 13. This second embodiment is characterized in that a through-hole is formed in the buffer connection portion, penetrating the buffer connection portion in the thickness direction. Note that the same reference numerals as in Figures 5 to 6 and Figures 8 to 9 indicate the same parts and locations, and therefore their description will be omitted unless necessary.

[0081] 10 and 11, a current collector body portion 46P is formed extending continuously from the inclined portion 45P, and a buffer connection portion 49PB is formed between the inclined portion 45P and the fixed base 41P. Therefore, when viewed from at least the tip end 47P side, the current collector body portion 46P, the inclined portion 45P, the buffer connection portion 49PB, and the fixed base 41P form the positive electrode side current collector plate 14P.

[0082] The current collector body 46P, inclined portion 45P, buffer connection portion 49PB, and fixed base 41P are formed by punching a flat aluminum-based material and bending it into a predetermined shape. As can be seen from Fig. 13, the buffer connection portion 49PB, inclined portion 45P, and current collector body 46P each have a continuous flat surface. The negative current collector 14N has a flat connection portion 48N instead of the buffer connection portion 49PB.

[0083] As mentioned above, copper-based materials have a higher specific gravity than aluminum-based materials. As a result, copper-based materials are less susceptible to vibration due to ultrasonic welding, and the vibration energy is smaller. Therefore, mechanical vibration is less of a problem with copper-based materials than with aluminum-based materials. This is because the negative electrode current collector plate 14N made of a copper-based material in this embodiment is less affected by mechanical vibration than aluminum-based materials, so the buffer connection 49N is not intentionally formed on the negative electrode current collector plate 14N made of a copper-based material. Of course, if the negative electrode current collector plate 14N is also affected by mechanical vibration, a configuration similar to the buffer connection 49PB can be used.

[0084] Here, as shown in Figure 3, the inclined portion 45P is also formed for the purpose of bringing the current collector body portion 46P closer to the positive electrode side bundling flat portion 301d in order to join the current collector body portion 46P and the positive electrode side bundling flat portion 301d.

[0085] The current collector body 46P is an overlapping region that is overlapped so as to come into contact with the positive electrode-side bundling flat plate portion 301d, and a joint region 42P is set within the overlapping region. This joint region 42P is formed up to the vicinity of the tip end 47P of the current collector body 46P.

[0086] Next, the specific configuration of the positive electrode side current collector 14P will be described with reference to Figures 12 and 13. Figure 12 shows the appearance of the positive electrode side current collector 14P as seen from the side where the anvil comes into contact, and Figure 13 shows the appearance of the positive electrode side current collector 14P as seen from the side where the bonding region 42P is formed.

[0087] 12 and 13, the positive electrode side current collector 14P is formed by punching a flat plate made of an aluminum-based material into a predetermined shape and then bending the punched flat plate into a predetermined shape, thereby forming the positive electrode side current collector 14P having the form shown in FIGS. 12 and 13.

[0088] A current collector 44P is formed on the side of the flat fixed base 41P, bent in a direction perpendicular to the plane of the fixed base 41P. The current collector 44P has a generally elongated rectangular (strip-like) shape with a predetermined width and thickness, and is integrally formed with a buffer connection portion 49PB, an inclined portion 45P, and a current collector main body portion 46P in this order as seen from the fixed base 41P up to the tip portion 47P.

[0089] 12, the current collector body 46P has, on one surface, a flat portion 46Pf with which an anvil 51 used for ultrasonic welding comes into contact, and, as shown in Fig. 13, on the other surface, a flat portion 46Pr that is joined to the positive electrode side bundling flat portion 301d of the electrode body 13. After ultrasonic welding is performed, a joining mark 52P caused by the anvil is formed on the flat portion 46Pf, and a joining region 42P is formed on the flat portion 46Pr.

[0090] As described above, the inclined portion 45P formed continuously with the current collector body portion 46P is formed to bring the current collector body portion 46P closer to the positive electrode side bundling flat plate portion 301d, making it easier to join the current collector body portion 46P and the positive electrode side bundling flat plate portion 301d. If the current collector body portion 46P and the positive electrode side bundling flat plate portion 301d can be joined without this inclined portion 45P, the inclined portion 45P can be omitted.

[0091] A buffer connection portion 49PB is integrally formed on the positive current collector plate 14P as a connection portion connecting the inclined portion 45P and the fixed base 41P. Here, the buffer connection portion 49PB has a function of weakening or absorbing mechanical force due to mechanical vibrations caused by ultrasonic welding, and the buffer connection portion 49PB is formed on a flat portion 49PP formed between the inclined portion 45P and the fixed base 41P.

[0092] That is, the buffer connection portion 49PB is formed by a flat portion 49PP formed between the inclined portion 45P and the fixed base portion 41P, and a through-hole 53 that penetrates the flat portion 49PP in the thickness direction. The shape of the through-hole 53 is rectangular, but is not limited to this and various shapes of through-holes may be used.

[0093] The buffer connection portion 49PB has a shape that is easy to elastically deform, or in other words, easy to move, because of the presence of the through-hole 53, and has a smaller rigidity than the current collector main body portion 46P and the inclined portion 45P. Therefore, mechanical vibrations acting on the current collector main body portion 46P are propagated to the inclined portion 45P, but because the rigidity of the buffer connection portion 49PB is set to be small, the buffer connection portion 49PB deforms between the current collector main body portion 46P and the inclined portion 45P, and functions to attenuate or absorb the mechanical vibrations.

[0094] In this way, in the positive electrode side current collector plate 14P of this embodiment, a buffer connection portion 49PB is formed between the fixed base portion 41P and the inclined portion 45P, making it possible to effectively suppress or absorb the energy of mechanical vibrations.

[0095] In the above-described embodiment, a buffer connection portion 49PB is formed between the fixed base portion 41P and the inclined portion 45P, but the basic idea is that it is sufficient that the buffer connection portion 49PB is formed between the fixed base portion 41P and the bonding area portion 42P.

[0096] In this way, the buffer connection portion 49PB needs only to be formed in a shape that is less rigid than the fixed base and the forming portion of the joint area portion of the current collector plate in order to weaken or absorb the mechanical force based on mechanical vibrations.

[0097] Next, a third embodiment of the present invention will be described with reference to Figures 14 to 17. This third embodiment is characterized in that alternating notches are formed in the buffer connection portion. Note that the same reference numerals as in Figures 5 to 6 and Figures 8 to 9 indicate the same parts and portions, and therefore their description will be omitted unless necessary.

[0098] 14 and 15 , a current collector body 46P is formed extending continuously from the inclined portion 45P, and a buffer connection portion 49PC is formed between the inclined portion 45P and the fixed base 41P. Therefore, when viewed from at least the tip end 47P side, the current collector body 46P, the inclined portion 45P, the buffer connection portion 49PC, and the fixed base 41P form the positive electrode side current collector plate 14P.

[0099] The current collector body 46P, inclined portion 45P, buffer connection portion 49PC, and fixed base 41P are formed by punching a flat aluminum-based material and bending it into a predetermined shape. As can be seen from Fig. 17, the buffer connection portion 49PC, inclined portion 45P, and current collector body 46P each have a continuous flat surface. Note that the negative current collector 14N has a flat connection portion 48N instead of the buffer connection portion 49PC.

[0100] As mentioned above, 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 vibrations are not as much of a problem with copper-based materials as they are with aluminum-based materials.

[0101] Here, as shown in Figure 3, the inclined portion 45P is also formed for the purpose of bringing the current collector body portion 46P closer to the positive electrode side bundling flat portion 301d in order to join the current collector body portion 46P and the positive electrode side bundling flat portion 301d.

[0102] The current collector body 46P is an overlapping region that is overlapped so as to come into contact with the positive electrode-side bundling flat plate portion 301d, and a joint region 42P is set within the overlapping region. This joint region 42P is formed up to the vicinity of the tip end 47P of the current collector body 46P.

[0103] Next, the specific configuration of the positive electrode side current collector 14P will be described with reference to Figures 16 and 17. Figure 16 shows the appearance of the positive electrode side current collector 14P as seen from the side where the anvil comes into contact, and Figure 17 shows the appearance of the positive electrode side current collector 14P as seen from the side where the bonding region 42P is formed.

[0104] 16 and 17, the positive electrode side current collector 14P is formed by punching a flat plate made of an aluminum-based material into a predetermined shape and then bending the punched flat plate into a predetermined shape, thereby forming the positive electrode side current collector 14P having the form shown in FIGS. 16 and 17.

[0105] A current collector 44P is formed on the side of the flat fixed base 41P, bent in a direction perpendicular to the plane of the fixed base 41P. The current collector 44P has a generally elongated rectangular (strip-like) shape with a predetermined width and thickness, and is integrally formed with a buffer connection portion 49PC, an inclined portion 45P, and a current collector main body portion 46P, which are formed in this order as seen from the fixed base 41P, up to the tip portion 47P.

[0106] 16, the current collector body 46P has, on one surface, a flat portion 46Pf with which an anvil 51 used for ultrasonic welding comes into contact, and, as shown in Fig. 17, on the other surface, a flat portion 46Pr that is joined to the positive electrode-side bundling flat portion 301d of the electrode body 13. After ultrasonic welding is performed, a joining mark 52P from the anvil is formed on the flat portion 46Pf, and a joining region 42P is formed on the flat portion 46Pr.

[0107] As described above, the inclined portion 45P formed continuously with the current collector body portion 46P is formed to bring the current collector body portion 46P closer to the positive electrode side bundling flat plate portion 301d, making it easier to join the current collector body portion 46P and the positive electrode side bundling flat plate portion 301d. If the current collector body portion 46P and the positive electrode side bundling flat plate portion 301d can be joined without this inclined portion 45P, the inclined portion 45P can be omitted.

[0108] A buffer connection portion 49PC is integrally formed on the positive current collector plate 14P as a connection portion connecting the inclined portion 45P and the fixed base 41P. Here, the buffer connection portion 49PC has the function of weakening or absorbing the mechanical force caused by the mechanical vibrations due to ultrasonic welding, and the buffer connection portion 49PC is formed on a flat portion 49PP formed between the inclined portion 45P and the fixed base 41P.

[0109] That is, the buffer connection portion 49PC is formed by a flat portion 49PP formed between the inclined portion 45P and the fixed base portion 41P and a notch 54 penetrating the flat portion 49PP. A plurality of the notches 54 are formed alternately on the opposing side surfaces of the flat portion 49PP. Therefore, a connection portion having a bent zigzag shape is formed on the flat portion 49PP.

[0110] The presence of the cutouts 54 makes the buffer connection portion 49PC less rigid and more easily deformed, in other words, more easily movable, than the rigidity of the current collector main body portion 46P and the inclined portion 45P. Therefore, mechanical vibrations acting on the current collector main body portion 46P are transmitted to the inclined portion 45P, but because the rigidity of the buffer connection portion 49PC is set to be small, the buffer connection portion 49PC deforms between the current collector main body portion 46P and the inclined portion 45P, and functions to attenuate or absorb the mechanical force caused by the vibrations.

[0111] In this way, in the positive electrode side current collector plate 14P of this embodiment, the buffer connection portion 49PC is formed between the fixed base portion 41P and the inclined portion 45P, so that it is possible to effectively suppress mechanical vibrations.

[0112] In the above-described embodiment, a buffer connection portion 49PC is formed between the fixed base portion 41P and the inclined portion 45P, but the basic idea is that it is sufficient that a buffer connection portion 49PC is formed between the fixed base portion 41P and the bonding area portion 42P.

[0113] In this way, the buffer connection portion 49PC is required to be formed in a shape that is less rigid than the fixed base and the portion forming the joining area of ​​the current collector plate in order to weaken or absorb the mechanical force due to mechanical vibration.

[0114] Next, a fourth embodiment of the present invention will be described with reference to Figures 18 to 21. This fourth embodiment is characterized by the formation of a stepped portion in the buffer connection portion. Note that the same reference numerals as in Figures 5 to 6 and Figures 8 to 9 indicate the same parts and portions, and therefore their description will be omitted unless necessary.

[0115] 18 and 19, a buffer connection portion 49PD is formed instead of the inclined portion 45P, and the buffer connection portion 49PD is formed between the current collector body portion 46P and the fixed base portion 41P. Therefore, when viewed at least from the tip portion 47P side, the positive electrode side current collector plate 14P is formed by the current collector body portion 46P, the buffer connection portion 49PD, and the fixed base portion 41P.

[0116] The current collector body 46P, buffer connection portion 49PD, and fixed base 41P are formed by punching a flat aluminum-based material and bending it into a predetermined shape. The negative current collector 14N is provided with a flat connection portion 48N instead of the buffer connection portion 49PD. This is because, as mentioned above, mechanical vibrations are not a significant problem when using copper-based materials.

[0117] Here, as shown in Figure 3, the buffer connection portion 49PD joins the current collector body portion 46P and the positive electrode side bundling flat plate portion 301d, and therefore also has the function of bringing the current collector body portion 46P closer to the positive electrode side bundling flat plate portion 301d.

[0118] The current collector body 46P is an overlapping region that is overlapped so as to come into contact with the positive electrode-side bundling flat plate portion 301d, and a joint region 42P is set within the overlapping region. This joint region 42P is formed up to the vicinity of the tip end 47P of the current collector body 46P.

[0119] Next, the specific configuration of the positive current collector 14P will be described with reference to Figures 20 and 21. Figure 20 shows the appearance of the positive current collector 14P as seen from the side where the joint region 42P is formed, and Figure 21 shows the appearance of the positive current collector as seen from the side.

[0120] 20 and 21, the positive electrode side current collector 14P is formed by punching a flat plate made of an aluminum-based material into a predetermined shape and then bending the punched flat plate into a predetermined shape, thereby forming the positive electrode side current collector 14P having the form shown in FIGS. 20 and 21.

[0121] A current collector 44P is formed on the side of the flat fixed base 41P, bent in a direction perpendicular to the plane of the fixed base 41P. The current collector 44P has a generally elongated rectangular (strip-like) shape with a predetermined width and thickness, and is integrally formed with a buffer connection portion 49PD and a current collector main body portion 46P, in that order, as seen from the fixed base 41P up to the tip portion 47P.

[0122] As in the embodiment described above (see, for example, FIG. 8 ), the current collector body 46P has, on one surface, a flat portion 46Pf with which the anvil 51 used for ultrasonic welding comes into contact, and, as shown in FIG. 20 , on the other surface, a flat portion 46Pr that is joined to the positive electrode-side bundling flat portion 301d of the electrode body 13. After ultrasonic welding is performed, a joining mark 52P by the anvil is formed on the flat portion 46Pf, and a joining region 42P is formed on the flat portion 46Pr.

[0123] A buffer connection portion 49PD is integrally formed on the positive-side current collector plate 14P as a connection portion connecting the current collector main body portion 46P and the fixed base portion 41P. This buffer connection portion 49PD also has the function of the inclined portion 45P described in the previous embodiment, and brings the current collector main body portion 46P closer to the positive-side bundling flat plate portion 301d, making it easier to join the current collector main body portion 46P and the positive-side bundling flat plate portion 301d.

[0124] Here, the buffer connection portion 49PD has the function of weakening or absorbing the mechanical force based on the mechanical vibration caused by ultrasonic welding, and the buffer connection portion 49PD is formed between the current collecting body portion 46P and the fixed base portion 41P.

[0125] That is, the buffer connection portion 49PD is formed by a flat portion 49PP formed between the current collecting body portion 46P and the fixed base 41P, and a plurality of stepped steps 55 connected to the flat portion 49PP. The stepped steps 55 extend from the flat portion 49PP toward the current collecting body portion 46P, changing their positions in a stepped manner relative to the current collecting body portion 46P.

[0126] The stepped buffer connection 49PD can increase the vibration propagation distance between the fixed base 41P and the joint area 42P compared to the flat connection 48N of the negative current collector 14N, thereby attenuating mechanical vibration. More importantly, the stepped buffer connection 49PD also has elasticity, which allows the current collector 44P to move more freely, thereby effectively attenuating mechanical vibration.

[0127] In this way, in the positive electrode side current collector plate 14P of this embodiment, a stepped buffer connection portion 49PD is formed between the fixed base 41P and the current collector main body portion 46P, making it possible to effectively suppress mechanical vibrations.

[0128] In this way, it is sufficient that the buffer connection portion 49PD is formed in a shape that has elasticity to weaken or absorb mechanical forces due to mechanical vibrations.

[0129] Although several embodiments have been described above, in summary, 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 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 fixed to the battery lid via a fixed base, and the other side of the current collector plate is joined to the electrode body via a bonding area, and a buffer connection portion is formed between the fixed base and the bonding area that weakens or absorbs mechanical forces due to mechanical vibrations caused by ultrasonic welding.

[0130] According to this, a buffer connection is formed between the joint of the current collecting plate and the fixed base, so that the mechanical force caused by the mechanical vibrations of ultrasonic welding acting on the battery lid is weakened or absorbed by the buffer connection, thereby suppressing damage to the gas exhaust valve and reducing the defect rate.

[0131] 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.

[0132] 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...fixing base, 42P, 42N...bonding region, 44P, 44N...current collector, 45P, 45N...inclined portion, 46P, 46N...current collector main body, 47P, 47N...tip, 48P...connection portion, 49P...buffer connection portion, 50...ultrasonic horn, 51...anvil.

Claims

1. A secondary battery comprising: an electrode assembly including a positive electrode material and a negative electrode material; a battery container that houses the electrode assembly; a battery lid that seals the battery container; a current collector plate disposed inside the battery container and joined to the electrode assembly by ultrasonic welding; an external electrode terminal provided on the outer surface of the battery lid and connected to the current collector plate; and a gas release valve provided on the battery lid, wherein one side of the current collector plate is fixed to the battery lid via a fixing base, and the other side of the current collector plate is joined to the electrode assembly via a bonding area, and a buffer connection is formed between the fixing base and the bonding area.

2. The secondary battery according to claim 1, wherein the buffer connection part is formed in a shape that has elasticity.

3. A secondary battery as claimed in claim 2, wherein the current collecting plate is formed from a single flat plate, and the fixed base, the buffer connection portion, the inclined portion, and the current collecting body portion on which the joining area portion is formed are arranged in this order, and the inclined portion and the current collecting body portion each have a continuous flat surface, and further the inclined portion is formed with an inclination to bring the current collecting body portion closer to the electrode body.

4. A secondary battery as claimed in claim 3, characterized in that the buffer connection part is located between the fixed base and the inclined part and is formed from a protruding part that protrudes in the same direction as the inclination of the inclined part.

5. A secondary battery according to claim 4, wherein the cross-sectional shape of the protrusion constituting the buffer connection part in the inclined direction is any one of an arc, a triangle, or a trapezoid.

6. A secondary battery according to claim 5, characterized in that the protrusions constituting the buffer connection are formed so that the tips of the protrusions do not extend beyond the current collector body portion that is present in the direction of the inclination of the inclined portion.

7. A secondary battery according to claim 3, characterized in that the buffer connection portion is located between the fixed base and the current collector body portion and is formed of a plurality of stepped steps that also serve as the inclined portion.

8. A secondary battery according to claim 1, wherein the buffer connection portion is formed in a shape that is less rigid than the fixed base and the portion of the current collector plate where the joining area is formed.

9. A secondary battery as claimed in claim 8, wherein the current collecting plate is formed from a single flat plate, and the fixed base, the buffer connection portion, the inclined portion, and the current collecting body portion on which the bonding area portion is formed are arranged in that order, and the buffer connection portion, the inclined portion, and the current collecting body portion each have a continuous flat portion, and further the inclined portion is formed with an inclination to bring the current collecting body portion closer to the electrode body.

10. A secondary battery according to claim 9, wherein the flat surface of the buffer connection part is formed with a through hole penetrating the flat surface.

11. A secondary battery according to claim 9, wherein the flat surface of the buffer connection part has alternating cutouts formed therein that penetrate the flat surface from the side surface of the flat surface.

12. A battery pack constructed by stacking a plurality of secondary batteries, each of which has an electrode body having 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 secondary battery uses the secondary battery described in any one of claims 1 to 11.

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