Patent Publication Number: US-2022231388-A1

Title: Terminal component, secondary battery, and battery pack

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present disclosure relates to a terminal component, a secondary battery, and a battery pack. The present application claims priority based on Japanese Patent Application No. 2021-008264 filed on Jan. 21, 2021, and the entire contents of the application are incorporated herein by reference. 
     2. Description of the Related Art 
     Japanese Patent Application Publication No. 2016-18675 discloses a secondary battery provided with external terminals of a positive electrode and a negative electrode that are composed of different materials. Such secondary batteries are connected in series by a bus bar made of the same material as that of one external terminal of the external terminals of the positive electrode and the negative electrode. A metal member composed of a material having excellent weldability to the material of the one external terminal is ultrasonically joined to the other external terminal. 
     Japanese Patent Application Publication No. 2011-124024 discloses a battery pack in which a plurality of cells is connected by a bus bar. Of the positive electrode terminal and the negative electrode terminal constituting the cell, the terminal having one polarity includes an external terminal having better welding quality with the bus bar and a base to which a foil having the one polarity is connected. The base and the external terminal are joined by ultrasonic joining. 
     SUMMARY OF THE INVENTION 
     When dissimilar metals are joined by ultrasonic joining, a horn is pressed against one metal and an ultrasonic vibration is applied while pressurizing to join the one metal to the other metal. At this time, for example, the metal to which the horn is applied may be deformed so that the edge portion of the metal protrudes or so that a part thereof is curved. 
     Such deformation can occur when performing ultrasonic joining to join dissimilar metals with respect to a terminal to be used in a battery. According to the findings of the present inventor, when such deformation occurs in a terminal to be used in a battery, the deformed portion may penetrate a member such as a gasket that insulates the terminal and a lid and may interfere with other members. Further, where the deformed portion is detached during the manufacturing process, the detached portion may enter the inside of the battery case and cause an internal short circuit. Where a portion of the terminal that becomes a bus bar connection surface is deformed, a gap may appear between the bus bar and the bus bar connection surface, which may cause welding defects. 
     The terminal component disclosed herein includes a first metal and a second metal overlapped on the first metal. At a boundary between the first metal and the second metal, there is a joint portion in which the first metal and the second metal are joined by metal joining. The second metal has a groove on the outside of the joint portion on the surface opposite to the surface overlapping on the first metal. 
     The second metal constituting the terminal component has a groove around the joint portion on the surface opposite to the joint portion. By forming such a groove, deformation of the terminal component due to ultrasonic joining can be suppressed. 
     The groove of the terminal component may be continuous in the circumferential direction. The first metal and the second metal may be composed of dissimilar metals. 
     A secondary battery provided with a battery case and an electrode terminal attached to the battery case may include a part configured of the terminal component described above. 
     In a battery pack including a plurality of secondary batteries having external terminals of positive electrodes and negative electrodes and a bus bar that connects the plurality of secondary batteries via the external terminals, at a boundary between an external terminal of one polarity, among the external terminals, and the bus bar, there may be a joint portion in which the external terminal of the one polarity and the bus bar are joined by metal joining, and the bus bar may have a groove on the outside of the joint portion on the surface opposite to the joint portion. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a partial cross-sectional view of a lithium ion secondary battery  10 ; 
         FIG. 2  is a cross-sectional view showing a II-II cross section of  FIG. 1 ; 
         FIG. 3  is a sectional view taken along line of  FIG. 2 ; 
         FIG. 4  is a cross-sectional view schematically showing a terminal component  200 ; 
         FIG. 5  is a cross-sectional view illustrating a method of manufacturing the terminal component  200 ; 
         FIG. 6  is a perspective view schematically showing a battery pack  100 ; and 
         FIG. 7  is a cross-sectional view schematically showing a portion of the battery pack  100  where an external terminal  43   b  of a negative electrode and a bus bar  91  are connected. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Hereinafter, embodiments of the terminal component and the secondary battery disclosed herein will be described. The embodiments described herein are, of course, not intended to specifically limit the present disclosure. The present disclosure is not limited to the embodiments described herein, unless otherwise specified. Each drawing is schematically drawn and does not necessarily reflect the actual configuration. In addition, members and parts that perform the same action are designated, as appropriate, by the same reference numerals, and duplicate description thereof will be omitted. 
     Secondary Battery 
     In the present description, the “secondary battery” means a device capable of charging and discharging. The secondary battery is inclusive of a battery generally called a lithium ion battery, a lithium secondary battery, or the like, a lithium polymer battery, a lithium ion capacitor, or the like. Here, a lithium ion secondary battery will be illustrated as a form of the secondary battery. 
     Lithium-Ion Secondary Battery  10   
       FIG. 1  is a partial cross-sectional view of a lithium ion secondary battery  10 . In  FIG. 1 , a state in which the inside is exposed is drawn along a wide surface on one side of a substantially rectangular parallelepiped battery case  41 . The lithium ion secondary battery  10  shown in  FIG. 1  is a so-called sealed battery.  FIG. 2  is a cross-sectional view showing a II-II cross section of  FIG. 1 . In  FIG. 2 , a partial cross-sectional view of a substantially rectangular parallelepiped battery case  41  in a state where the inside is exposed along a narrow surface on one side is schematically drawn. 
     As shown in  FIG. 1 , the lithium ion secondary battery  10  includes an electrode body  20 , a battery case  41 , a positive electrode terminal  42 , and a negative electrode terminal  43 . 
     Electrode Body  20   
     The electrode body  20  is accommodated in the battery case  41  in a state of being covered with an insulating film (not shown) or the like. The electrode body  20  includes a positive electrode sheet  21  as a positive electrode element, a negative electrode sheet  22  as a negative electrode element, and separator sheets  31  and  32  as separators. The positive electrode sheet  21 , the first separator sheet  31 , the negative electrode sheet  22 , and the second separator sheet  32  are long strip-shaped members, respectively. 
     In the positive electrode sheet  21 , a positive electrode active material layer  21   b  including a positive electrode active material is formed on both sides of a positive electrode current collecting foil  21   a  (for example, an aluminum foil) having a predetermined width and thickness, except for a non-formation portion  21   a   1  that is set to a constant width at one end in the width direction. For example, in a lithium ion secondary battery, the positive electrode active material is a material capable of releasing lithium ions during charging and absorbing lithium ions during discharging, such as a lithium transition metal composite material. Various positive electrode active materials have been generally proposed in addition to the lithium transition metal composite material, and the type of the positive electrode active material is not particularly limited. 
     In the negative electrode sheet  22 , a negative electrode active material layer  22   b  including a negative electrode active material is formed on both sides of a negative electrode current collecting foil  22   a  (here, a copper foil) having a predetermined width and thickness, except for a non-formation portion  22   a   1  that is set to a constant width at one end in the width direction. For example, in a lithium ion secondary battery, the negative electrode active material is a material capable of occluding lithium ions during charging and releasing the occluded lithium ions during discharging, such as natural graphite. Various negative electrode active materials have been generally proposed in addition to natural graphite, and the type of the negative electrode active material is not particularly limited. 
     For the separator sheets  31  and  32 , for example, a porous resin sheet which has a required heat resistance and through which an electrolyte can pass is used. Various separator sheets have been proposed for the separator sheets  31  and  32 , and the type thereof is not particularly limited. 
     Here, the negative electrode active material layer  22   b  is formed, for example, to be wider than the positive electrode active material layer  21   b . The width of the separator sheets  31  and  32  is larger than that of the negative electrode active material layer  22   b . The non-formation portion  21   a   1  of the positive electrode current collecting foil  21   a  and the non-formation portion  22   a   1  of the negative electrode current collecting foil  22   a  are directed to opposite sides in the width direction. Further, the positive electrode sheet  21 , the first separator sheet  31 , the negative electrode sheet  22 , and the second separator sheet  32  are oriented in the length direction, stacked in this order and wound. The negative electrode active material layer  22   b  covers the positive electrode active material layer  21   b  with the separator sheets  31  and  32  interposed therebetween. The negative electrode active material layer  22   b  is covered with separator sheets  31  and  32 . The non-formation portion  21   a   1  of the positive electrode current collecting foil  21   a  protrudes from one side of the separator sheets  31  and  32  in the width direction. The non-formation portion  22   a   1  of the negative electrode current collecting foil  22   a  protrudes from the separator sheets  31  and  32  on the opposite side in the width direction. 
     As shown in  FIG. 1 , the above-described electrode body  20  is flattened along one plane including the winding axis so as to be accommodated in the case body  41   a  of the battery case  41 . The non-formation portion  21   a   1  of the positive electrode current collecting foil  21   a  is arranged on one side, and the non-formation portion  22   a   1  of the negative electrode current collecting foil  22   a  is arranged on the opposite side along the winding axis of the electrode body  20 . 
     Battery Case  41   
     As shown in  FIG. 1 , the electrode body  20  is accommodated in the battery case  41 . The battery case  41  has a case body  41   a  having a substantially rectangular parallelepiped angular shape with one side open, and a lid  41   b  mounted on the opening. In this embodiment, the case body  41   a  and the lid  41   b  are formed of aluminum or an aluminum alloy mainly composed of aluminum, from the viewpoint of weight reduction and ensuring the required rigidity. 
     Case Body  41   a    
     As shown in  FIGS. 1 and 2 , the case body  41   a  has a substantially rectangular parallelepiped angular shape with one side open. The case body  41   a  has a substantially rectangular bottom surface portion  61 , a pair of wide surface portions  62  and  63 , and a pair of narrow surface portions  64  and  65 . Each of the pair of wide surface portions  62  and  63  rises from the long side of the bottom surface portion  61 . Each of the pair of narrow surface portions  64  and  65  rises from the short side of the bottom surface portion  61 . An opening  41   a   1  surrounded by a pair of wide surface portions  62  and  63  and a pair of narrow surface portions  64  and  65  is formed on one side surface of the case body  41   a.    
     Lid  41   b    
     The lid  41   b  is mounted on the opening  41   a   1  of the case body  41   a  surrounded by the long sides of the pair of wide surface portions  62  and  63  and the short sides of the pair of narrow surface portions  64  and  65 . The peripheral edge of the lid  41   b  is joined to the edge of the opening  41   a   1  of the case body  41   a . Such joining may be performed by, for example, continuous welding with no gaps. Such welding can be achieved, for example, by laser welding. 
     In this embodiment, a positive electrode terminal  42  and a negative electrode terminal  43  are attached to the lid  41   b . The positive electrode terminal  42  includes an internal terminal  42   a  and an external terminal  42   b . The negative electrode terminal  43  includes an internal terminal  43   a  and an external terminal  43   b . The internal terminals  42   a  and  43   a  are attached to the inside of the lid  41   b  with an insulator  72  interposed therebetween. The external terminals  42   b  and  43   b  are attached to the outside of the lid  41   b  with a gasket  71  interposed therebetween. The internal terminals  42   a  and  43   a  extend inside the case body  41   a . The internal terminal  42   a  of the positive electrode is connected to the non-formation portion  21   a   1  of the positive electrode current collecting foil  21   a . The internal terminal  43   a  of the negative electrode is connected to the non-formation portion  22   a   1  of the negative electrode current collecting foil  22   a.    
     As shown in  FIG. 1 , the non-formation portion  21   a   1  of the positive electrode current collecting foil  21   a  of the electrode body  20  and the non-formation portion  22   a   1  of the negative electrode current collecting foil  22   a  are attached to the internal terminals  42   a  and  43   a  that are attached to both sides of the lid  41   b  in the longitudinal direction. The electrode body  20  is accommodated in the battery case  41  in a state of being attached to the internal terminals  42   a  and  43   a  attached to the lid  41   b . Here, the wound electrode body  20  is illustrated by way of example. The structure of the electrode body  20  is not limited to such a form. The structure of the electrode body  20  may be, for example, a laminated structure in which a positive electrode sheet and a negative electrode sheet are alternately laminated with a separator sheet interposed therebetween. Further, a plurality of electrode bodies  20  may be accommodated in the battery case  41 . 
       FIG. 3  is a sectional view taken along line of  FIG. 2 .  FIG. 3  shows a cross section of a part where the negative electrode terminal  43  is attached to the lid  41   b . In this embodiment, a member in which dissimilar metals are joined is used for the external terminal  43   b  of the negative electrode. In  FIG. 3 , the structure such as the groove in the metal constituting the external terminal  43   b , the interface between dissimilar metals, and the like are not shown, and the cross-sectional shape of the external terminal  43   b  is schematically shown. 
     As shown in  FIG. 3 , the lid  41   b  has an attachment hole  41   b   1  for attaching the external terminal  43   b  of the negative electrode. The attachment hole  41   b   1  penetrates the lid  41   b  at a predetermined position of the lid  41   b . The internal terminal  43   a  and the external terminal  43   b  of the negative electrode are attached to the attachment hole  41   b   1  of the lid  41   b  with the gasket  71  and the insulator  72  interposed therebetween. On the outside of the attachment hole  41   b   1 , a step  41   b   2  on which the gasket  71  is mounted is provided around the attachment hole  41   b   1 . The step  41   b   2  is provided with a seat surface  41   b   3  on which the gasket  71  is arranged. The seat surface  41   b   3  is provided with a projection  41   b   4  for positioning the gasket  71 . 
     Here, as shown in  FIG. 3 , the external terminal  43   b  of the negative electrode includes a head  43   b   1 , a shaft  43   b   2 , and a caulking piece  43   b   3 . The head  43   b   1  is a part arranged outside the lid  41   b . The head  43   b   1  is a part that is larger than the attachment hole  41   b   1  and is arranged at the gasket  71 . The shaft  43   b   2  is a part mounted in the attachment hole  41   b   1  with the gasket  71  interposed therebetween. The shaft  43   b   2  protrudes downward from a substantially central portion of the head  43   b   1 . As shown in  FIG. 3 , the caulking piece  43   b   3  is a part caulked to the internal terminal  43   a  of the negative electrode inside the lid  41   b . The caulking piece  43   b   3  extends from the shaft  43   b   2  and is bent and caulked to the internal terminal  43   a  of the negative electrode after being inserted into the lid  41   b.    
     Gasket  71   
     As shown in  FIG. 3 , the gasket  71  is a member attached to the attachment hole  41   b   1  and the seat surface  41   b   3  of the lid  41   b . In this embodiment, the gasket  71  includes a seat  71   a , a boss  71   b , and a side wall  71   c . The seat  71   a  is a part mounted on the seat surface  41   b   3  provided on the outer surface around the attachment hole  41   b   1  of the lid  41   b . The seat  71   a  has a substantially flat surface corresponding to the seat surface  41   b   3 . The seat  71   a  is provided with a depression corresponding to the projection  41   b   4  of the seat surface  41   b   3 . The boss  71   b  projects from the bottom surface of the seat  71   a . The boss  71   b  has an outer shape along the inner side surface of the attachment hole  41   b   1  so as to be mounted on the attachment hole  41   b   1  of the lid  41   b . The inner surface of the boss  71   b  serves as a mounting hole for mounting the shaft  43   b   2  of the external terminal  43   b . The side wall  71   c  rises upward from the peripheral edge of the seat  71   a . The head  43   b   1  of the external terminal  43   b  is mounted on a part surrounded by the side wall  71   c  of the gasket  71 . 
     The gasket  71  is arranged between the lid  41   b  and the external terminal  43   b  to ensure insulation between the lid  41   b  and the external terminal  43   b . Further, the gasket  71  ensures the airtightness of the attachment hole  41   b   1  of the lid  41   b . From this point of view, it is preferable to use a material having excellent chemical resistance and weather resistance. In this embodiment, PFA is used for the gasket  71 . PFA is a copolymer of tetrafluoroethylene and perfluoroalkoxyethylene (Tetrafluoroethylene Perfluoroalkylvinylether Copolymer). The material used for the gasket  71  is not limited to PFA. 
     Insulator  72   
     The insulator  72  is a member mounted inside the lid  41   b  around the attachment hole  41   b   1  of the lid  41   b . The insulator  72  includes a base  72   a , a hole  72   b , and a side wall  72   c . The base  72   a  is a part arranged along the inner surface of the lid  41   b . In this embodiment, the base  72   a  is a substantially flat plate-shaped part. The base  72   a  is arranged along the inner side surface of the lid  41   b , and has a size such that the base does not protrude from the lid  41   b  so that it can be housed in the case body  41   a . The hole  72   b  is provided correspondingly to the attachment hole  41   b   1 . In this embodiment, the hole  72   b  is provided in a substantially central portion of the base  72   a . On the side surface of the lid  41   b  facing the inner side surface, a recessed step  72   b   1  is provided around the hole  72   b . The step  72   b   1  accommodates the distal end of the boss  71   b  of the gasket  71  mounted in the attachment hole  41   b   1 . The side wall  72   c  rises downward from the peripheral edge of the base  72   a . A proximal portion  43   a   1  provided at one end of the internal terminal  43   a  of the negative electrode is accommodated in the base  72   a . Since the insulator  72  is arranged inside the battery case  41 , it is preferable that the insulator  72  has a required chemical resistance. In this embodiment, PPS is used for the insulator  72 . PPS is a polyphenylene sulfide resin. The material used for the insulator  72  is not limited to PPS. 
     The internal terminal  43   a  of the negative electrode includes the proximal portion  43   a   1  and a connection piece  43   a   2  (see  FIGS. 1 and 2 ). The proximal portion  43   a   1  is a part mounted on the base  72   a  of the insulator  72 , In this embodiment, the proximal portion  43   a   1  has a shape corresponding to the inside of the side wall  72   c  around the base  72   a  of the insulator  72 . As shown in  FIGS. 1 and 2 , the connection piece  43   a   2  extends from one end of the proximal portion  43   a   1  and extends into the case body  41   a  to be connected to the non-formation portion  22   a   1  of the negative electrode of the electrode body  20 . 
     In this embodiment, the gasket  71  is attached to the outside of the lid  41   b  while the boss  71   b  is being mounted on the attachment hole  41   b   1 . The external terminal  43   b  is mounted on the gasket  71 . At this time, the shaft  43   b   2  of the external terminal  43   b  is inserted into the boss  71   b  of the gasket  71 , and the head  43   b   1  of the external terminal  43   b  is arranged on the seat  71   a  of the gasket  71 . The insulator  72  and the internal terminal  43   a  are attached to the inside of the lid  41   b . As shown in  FIG. 3 , the caulking piece  43   b   3  of the external terminal  43   b  is bent and caulked to the proximal portion  43   a   1  of the internal terminal  43   a . The caulking piece  43   b   3  of the external terminal  43   b  and the proximal portion  43   a   1  of the negative electrode terminal  43  may be partially metal joined in order to improve conductivity. 
     For the internal terminal  42   a  of the positive electrode of the lithium ion secondary battery  10 , the required level of oxidation-reduction resistance is not higher than that of the negative electrode. From the viewpoint of required oxidation-reduction resistance and weight reduction, aluminum can be used for the internal terminal  42   a  of the positive electrode. By contrast, for the internal terminal  43   a  of the negative electrode, the required level of oxidation-reduction resistance is higher than that of the positive electrode. From this point of view, copper may be used for the internal terminal  43   a  of the negative electrode. Meanwhile, as the bus bar to which the external terminal  43   b  is connected, aluminum or an aluminum alloy may be used from the viewpoint of weight reduction and cost reduction. 
     The present inventor considered the use of copper or a copper alloy for the part of the external terminal  43   b  that is to be joined to the internal terminal  43   a , and the use of aluminum or an aluminum alloy for the part of the external terminal  43   b  that is to be connected to the bus bar. In order to realize such a structure, in this embodiment, a member obtained by joining copper and aluminum by dissimilar metal joining is used as the external terminal  43   b . Hereinafter, the structure of the terminal component  200  used as the external terminal  43   b  will be described. 
     Terminal Component  200   
       FIG. 4  is a cross-sectional view schematically showing the terminal component  200 .  FIG. 4  schematically shows a step of joining the first metal  201  and the second metal  202  constituting the terminal component  200 . As shown in  FIG. 3 , the terminal component  200  as the external terminal  43   b  is attached to the battery case  41  so that a part of the terminal component  200  is connected to the internal terminal  43   a  inside the battery case  41  and a part of the terminal component is exposed to the outside of the battery case  41 . 
     As shown in  FIG. 4 , the terminal component  200  includes a first metal  201  and a second metal  202  overlapped on the first metal  201 . The first metal  201  and the second metal  202  are configured of different metals. 
     The first metal  201  is a part that is connected by a portion thereof to the internal terminal  43   a  inside the battery case  41  when the terminal component  200  is used as the external terminal  43   b  (see  FIG. 3 ). In this embodiment, the first metal is configured of copper. The first metal  201  has a shaft  201   a  and a flange  201   b . The shaft  201   a  is a part serving as the shaft  43   b   2  to be inserted into the attachment hole  41   b   1  of the lid  41   b . The flange  201   b  is a flat plate-shaped part provided at one end of the shaft  201   a  and wider than the shaft  201   a . The shaft  201   a  is provided with a part  201   c  that serves as a caulking piece  43   b   3  that is further caulked to the internal terminal  43   a  on the side opposite to the side on which the flange  201   b  is provided. 
     The second metal  202  is a part exposed to the outside of the battery case  41  when the terminal component  200  is used as the external terminal  43   b  (see  FIG. 3 ). As the second metal  202 , a metal having malleability and lower rigidity than the first metal  201  is used. In this embodiment, the second metal is configured of aluminum. The second metal  202  is a flat plate-shaped metal member overlapped on the first metal  201 . A surface  202   a  of the second metal  202  overlapped on the first metal  201  has a substantially rectangular shape corresponding to the end surface  201   b   1  of the first metal  201 . 
     The terminal component  200  has a joint portion  203  in which the first metal  201  and the second metal  202  are joined by metal joining at the boundary between the first metal  201  and the second metal  202 . In the joint portion  203 , the first metal  201  and the second metal  202  are solid-phase joined without an adhesive layer such as an adhesive or a solder. Such a joint portion  203  can be formed by joining the first metal  201  and the second metal  202  by a method such as ultrasonic pressure welding, friction welding, resistance welding, or the like. 
     The second metal  202  has a groove  202   c  on the outside of the joint portion  203  on the surface  202   b  opposite to the surface  202   a  overlapped on the first metal  201 . The groove  202   c  is formed on the outside of the portion where the joint portion  203  is projected perpendicularly to the surface  202   b . The joint portion  203  and the groove  202   c  may partially overlap each other. Further, the joint portion  203  may be partially outside the groove  202   c . When the groove  202   c  is continuously formed outside the joint portion  203 , the area inside the groove  202   c  may be larger than the area where the joint portion  203  is projected perpendicularly to the surface  202   b.    
     In this embodiment, the groove  202   c  is formed in a circumferential shape and is continuous in the circumferential direction. In this embodiment, an outer wall  202   c   1  of the groove  202   c  is perpendicular to the surface  202   b . An inner wall  202   c   2  of the groove  202   c  is perpendicular to the surface  202   b  near the boundary with a bottom portion  202   c   3 , but is inclined so as to approach the outer wall  202   c   1  as the distance from the bottom portion  202   c   3  increases. That is, an inner part  202   d  on the inside of the groove  202   c  expands toward a top portion  202   d   1 . Therefore, the area of the bottom portion  202   c   3  of the groove  202   c  is larger than the area of an opening  202   c   4 . The shape of the groove  202   c  is not particularly limited. The groove  202   c  may be formed in a polygonal shape such as a quadrangle. The groove  202   c  may not be formed continuously and may be formed intermittently. Further, the opening  202   c   4  of the groove  202   c  may be partially or wholly closed by the widening of the top portion  202   d   1  of the inner part  202   d.    
     In the embodiment shown in  FIG. 4 , the surface  202   b  of the second metal  202  and the top portion  202   d   1  of the inner part  202   d  are in the same plane. However, such a form is not limiting. The top portion  202   d   1  may protrude from the surface  202   b . Further, the top portion  202   d   1  may be pushed in more than the surface  202   b.    
     In the embodiment illustrated by  FIGS. 4 and 5 , it is shown how the first metal  201  and the second metal  202  are ultrasonically pressure-welded. As shown in  FIG. 5 , the second metal  202  has a groove  202   e  on the surface  202   b , which later becomes a groove  202   c . The groove  202   e  is formed in a circumferential shape. The groove  202   e  is continuously provided in the circumferential direction. Here, a bottom portion  202   e   1  of the groove  202   e  is parallel to the surface  202   b . An outer wall  202   e   2  of the groove  202   e  is perpendicular to the surface  202   b . The second metal  202  is provided with a protrusion  202   f  that serves as the inner part  202   d . A top portion  202   f   1  of the protrusion  202   f  is parallel to the surface  202   b . A side wall  202   f   2  of the protrusion  202   f  is perpendicular to the surface  202   b . The height of the protrusion  202   f  is larger than the depth of the groove  202   e . The protrusion  202   f  protrudes from the surface  202   b.    
       FIG. 5  is a cross-sectional view illustrating a method of manufacturing the terminal component  200 .  FIG. 5  shows a state before the first metal  201  and the second metal  202  are ultrasonically pressure-welded. First, the first metal  201  is placed in an anvil  301 , The second metal  202  is overlapped on the first metal  201 . A horn  302  is attached to the top portion  202   f   1  of the protrusion  202   f  of the second metal  202 . The second metal  202  is pressurized while applying the vibration required for ultrasonic pressure welding to the horn  302 . The pressure and ultrasonic vibration applied to the horn  302  are set, as appropriate, according to the metal type and dimensions of the first metal  201  and the second metal  202 . By pressurizing the second metal  202  while applying ultrasonic vibration, the joint portion  203  is formed at the boundary between the first metal  201  and the second metal  202 . At that time, a crush mark caused by pressing the horn  302  may be formed at a position on the top portion  201   d   1  corresponding to the joint portion  203 . 
     When the horn  302  is pressed against the second metal  202 , the second metal  202  is plastically deformed. At that time, since the groove  202   e  is provided, the plastic deformation of the second metal  202  occurs in the groove  202   e . In other words, the deformation of the protrusion  202   f  to which the horn  302  is applied extends only into the groove  202   e . As a result, deformation of the terminal component  200  is suppressed. In the embodiment shown in  FIG. 4 , the deformation occurs mainly in the portion of the inner part  202   d  near the top portion  202   d   1  so that the area of the opening  202   c   4  becomes smaller than the area of the bottom portion  202   c   3 . 
     The joint portion  203  may be obtained by joining by resistance welding, friction welding, or the like. Similarly, when metal joining is performed by such a method, deformation of the terminal component  200  due to pressurization is suppressed. 
     The dimensions of the groove  202   e  and the protrusion  202   f  may be set such that the groove  202   c  is not filled after metal joining. The volume of the groove  202   e  may be set to be larger than the volume of the portion  202   f   3  of the protrusion  202   f  protruding from the surface  202   b . By setting the volume of the groove  202   e  in this way, the deformation caused by pressurizing the top portion  202   f   1  of the protrusion  202   f  is localized in the groove  202   e . As a result, the influence of the deformation of the second metal  202  due to the pressurization on the outer shape of the terminal component  200  can be reduced. 
       FIG. 6  is a perspective view schematically showing the battery pack  100 . The battery pack  100  includes a plurality of secondary batteries  10  and a plurality of spacers  90 . Further, the battery pack  100  includes a restraint mechanism. Specifically, as shown in the figure, the battery pack  100  includes a pair of end plates  92 A and  92 B, a restraint band  94 , and a plurality of screws  96 . The pair of end plates  92 A and  92 B are arranged at both ends of the battery pack  100  in the arrangement direction of the secondary batteries  10 . The restraint band  94  is bridged over the pair of end plates  92 A and  92 B, and is attached to the pair of end plates  92 A and  92 B by screws  96 . The spacer  90  is sandwiched between two adjacent secondary batteries  10 . Further, one end spacer  98  is arranged between the secondary battery  10  and the end plate  92 A and the other is arranged between the secondary battery  10  and the end plate  92 B. The positive electrode terminals  42  and the negative electrode terminals  43  of the secondary batteries  10  constituting the battery pack  100  are electrically connected by bus bars  91 . As a result, the secondary batteries  10  constituting the battery pack  100  are electrically connected in series in order. However, the shape, size, number, arrangement, connection method, and the like of the secondary batteries  10  constituting the battery pack  100  are not limited to the modes disclosed herein, and can be changed as appropriate. 
     The terminal component  200  shown in  FIG. 4  is used as the external terminal  43   b  of the negative electrode of the lithium ion secondary battery  10 . The external terminal  43   b  is connected to the bus bar  91 . The external terminal  43   b  and the bus bar  91  can be welded by, for example, laser welding. Aluminum is used for the bus bar  91  from the viewpoint of weight reduction, and in the terminal component  200  proposed herein, aluminum can be used for the first metal  201  of the external terminal  436  of the negative electrode that is exposed to the outside of the lithium ion secondary battery  10 . The external terminal  42   b  of the positive electrode is configured of aluminum. Therefore, dissimilar metal joining does not occur in the joining between the bus bar  91  and the external terminal  43   b  of the negative electrode or the joining between the bus bar  91  and the external terminal  42   b  of the positive electrode, and a highly reliable joining in terms of strength can be realized. Further, with the terminal component  200 , the part  201   c  of the external terminal  43   b  of the negative electrode that is to be joined to the internal terminal  43   a  (see  FIGS. 2 and 3 ) inside the battery case  41  is the first metal  201  and is configured of copper. Therefore, dissimilar metal joining does not occur in the joining between the external terminal  43   b  and the internal terminal  43   a  of the negative electrode, and a highly reliable joining in terms of strength can be realized. 
     As shown in  FIG. 4 , the terminal component  200  proposed herein has a groove  202   c  on the surface  202   b  of the second metal  202  opposite to the surface  202   a  overlapping on the first metal  201 . The groove  202   c  is provided on the outside of the joint portion  203 . The joint portion  203  is obtained by metal joining by a method such as ultrasonic pressure welding, friction welding, resistance welding, or the like. Since the groove  202   c  is formed, the deformation of the second metal  202  due to pressure application when foiling the joint portion  203  is unlikely to extend to the outside of the groove  202   c . Therefore, the terminal component  200  having good dimensional accuracy is provided. In such a terminal component  200 , the possibility of the deformed portion being detached or interfere with other parts is reduced. Further, the bus bar connection surface of the terminal component  200  does not bend, and good connection with the bus bar can be realized. 
     Here, the groove  202   c  is continuous in the circumferential direction. When performing metal joining, deformation due to pressurization does not always occur at the same position. Since the groove  202   c  is continuous around the joint portion  203 , the occurrence of deformation of the outer shape of the terminal component  200  can be suppressed more suitably. 
     In the above-described embodiment, the groove  202   c  is provided on the outside of the joint portion  203  in which the first metal  201  and the second metal  202  are metal-joined, but this embodiment is not limiting. For example, for the purpose of improving the joining strength between the first metal  201  and the second metal  202 , a portion where the first metal  201  and the second metal  202  are metal-joined may be also present on the outside of the groove  202   c.    
     Further, the first metal  201  and the second metal  202  may have a portion joined by a joining other than the metal joining. In order to improve the joining strength or the like, for example, a structure obtained by caulking one metal with the other metal may be provided at the boundary between the first metal  201  and the second metal  202 . 
     A combination of metals constituting the first metal  201  and the second metal  202  is not limited to copper and aluminum, and various metal combinations can be adopted. Further, the first metal  201  and the second metal  202  may be subjected to a treatment such as plating. 
     As another aspect of the technique disclosed herein, a battery pack  100  in which the first metal  201  is used as the external terminal and the second metal  202  is used as the bus bar  91  is provided.  FIG. 7  is a cross-sectional view schematically showing a portion of the battery pack  100  in which the external terminal  43   b  of the negative electrode and the bus bar  91  are connected. In the embodiment shown in  FIG. 7 , the first metal  201  is used as the external terminal  43   b  of the negative electrode, and the second metal  202  is used as the bus bar  91 . Here, the second metal  202  is a long plate-shaped metal member made of aluminum. The surface  202   a  provided on one end of the second metal  202  is overlapped on the end surface  201   b   1  of the first metal  201 . Although not shown, the other end of the second metal  202  is connected to the external terminal  42   b  of the positive electrode. At the boundary between the external terminal  43   b  and the bus bar  91 , a joint portion  203  in which the external terminal  43   b  and the bus bar  91  are joined by metal joining is provided. The bus bar  91  has a groove  202   c  on the outside of the joint portion  203  on the surface  201   b  opposite to the joint portion  203 . 
     In the battery pack  100  having such a configuration, the external terminal  43   b  is configured of one kind of metal. Manufacturing costs are reduced due to the small number of parts. Since the bus bar  91  and the external terminal  43   b  are metal-joined, the conduction resistance is suppressed to a low level. Further, the bus bar  91  has a groove  202   c  on the outside of the joint portion  203 . As a result, deformation and bending are suppressed on the surface of the bus bar  91  to be joined to the external terminal  43   b , and good joining with the external terminal  43   b  can be realized. 
     The terminal component, secondary battery, and battery pack disclosed herein have been described in various ways. Unless otherwise specified, the embodiments of the terminal component and battery mentioned herein do not limit the present disclosure. Further, the secondary battery disclosed herein can be variously modified, and constituent elements thereof and processes referred to herein can be omitted, as appropriate, or combined, as appropriate, unless a specific problem occurs.