Abstract:
A bus bar, which is used with batteries wherein the positive terminal and the negative terminal are each formed from a different metal, and which has excellent mechanical strength and can suppress electrical resistance while preventing galvanic corrosion. The bus bar is bonded in one piece by metallically bonding: a cathode connector that is formed from the same metal as the positive terminal of a battery cell, and that can connect to the positive terminal; and an anode connector that is formed from the same metal as the negative terminal of the battery cell, and that can connect to the negative terminal.

Description:
TECHNICAL FIELD 
     The present invention relates to a busbar suitable for use with a battery including a positive terminal and a negative terminal formed of different metals and a method for manufacturing the busbar. 
     BACKGROUND ART 
     Assembled batteries in which a plurality of battery cells are connected to each other with busbars so that cathodes and anodes thereof are connected in series are known as batteries for electric vehicles, hybrid vehicles, etc. (see, for example, PTL 1). Such an assembled battery is characterized by having high power and high energy density, and in most cases includes lithium-ion batteries as the battery cells. Lithium-ion batteries include positive terminals formed of aluminum (Al) and negative terminals formed of copper (Cu). 
     Busbars (or bus bars, which are components used to distribute electric energy) are used to connect the terminals of the battery cells to each other. As disclosed in the Problems to be Solved by the Invention section of PTL 2, a busbar may be manufactured by connecting parts of the busbar together by laser beam welding. 
     CITATION LIST 
     Patent Literature 
     PTL 1: Japanese Unexamined Patent Application Publication No. 2002-373638 
     PTL 2: Japanese Unexamined Patent Application Publication No. 2003-163039 
     SUMMARY OF INVENTION 
     Technical Problem 
     In the case where the battery cells are connected to each other in series as described above, the positive terminals, which are made of aluminum, are connected to the negative terminals, which are made of copper, with the busbars. Therefore, whether the busbars are formed of aluminum or copper, connection between different metals is required between each busbar and one of the terminals connected thereto. 
     In general, it is commonly known that when different metals are connected to each other, galvanic corrosion (electrochemical corrosion) occurs due to moisture in the air. As the galvanic corrosion progresses, the busbar and the terminal may become electrically disconnected from each other. Also, the busbar or the terminal may become damaged. Consequently, a serious problem such as not being able to start the electric vehicle may occur. 
     As a countermeasure against this problem, PTL 2 proposes a method for manufacturing a busbar by bonding an aluminum piece and a copper piece together by laser beam welding. However, when a busbar is manufactured by this method, a eutectic of the two metals is formed at the laser-beam-welded part. This leads to an excessive electrical resistance and significant reduction in mechanical strength (in particular, brittleness and tensile strength). Therefore, the busbar manufactured by this method cannot be put into practical use. 
     The present invention has been made in view of the above-described circumstances, and an object of the present invention is to provide a high-performance, high-reliability busbar which is suitable for use with a battery including a positive terminal and a negative terminal formed of different metals, in which galvanic corrosion can be suppressed and an electrical resistance can be reduced, and which has high mechanical strength, and a method for manufacturing the busbar. 
     Solution to Problem 
     To achieve the above-described object, according to the present invention, a busbar for use with a battery including a positive terminal and a negative terminal formed of different metals, the busbar being used to connect the terminals, includes a cathode connector made of the same metal as the positive terminal of the battery and connectable to the positive terminal and an anode connector made of the same metal as the negative terminal of the battery and connectable to the negative terminal. The cathode connector and the anode connector are integrated together by metallic bonding. 
     With this busbar, a positive terminal of a battery may be connected to the cathode connector that is made of the same metal as the positive terminal, and a negative terminal of another battery may be connected to the anode connector that is made of the same metal as the negative terminal. Accordingly, galvanic corrosion at the parts connected to the terminals and an increase in electrical resistance due to the galvanic corrosion can be suppressed, and the reliability of the busbar used to connect the batteries can be increased. In addition, the cathode connector and the anode connector of the busbar are integrated together by metallic bonding, and therefore the galvanic corrosion and increase in electrical resistance due to the galvanic corrosion can also be suppressed at the bonding portion. 
     The term “metallic bonding” means that different metals that are to be bonded together form a bonding interface in which they are tightly bonded at the metal structural level so that conductivity and mechanical bonding strength are increased to “values suitable for a busbar in practical use”. 
     Preferably, the cathode connector is formed of aluminum or an aluminum alloy, and the anode connector is formed of copper or a copper alloy. 
     It is essential to manufacture the above-described busbar by a manufacturing method including preparing an opposing base material in which a metal base material that forms the cathode connector and a metal base material that forms the anode connector are in surface contact with each other and subjecting the opposing base material to extrusion or drawing using a die under a high hydrostatic pressure. 
     According to this manufacturing method, a busbar capable of appropriately connecting a positive terminal of a battery to a negative terminal of another battery can be manufactured by integrating the metal material that forms the cathode connector and the metal material that forms the anode connector together by metallic bonding. 
     To achieve the above-described object, according to the present invention, a busbar for use with a battery including a positive terminal and a negative terminal formed of different metals, the busbar being used to connect the terminals, includes a cathode connector made of the same metal as the positive terminal of the battery and connectable to the positive terminal and an anode connector made of the same metal as the negative terminal of the battery and connectable to the negative terminal. The cathode connector is surrounded by the anode cathode connector or the anode cathode connector is surrounded by the cathode connector in plan view. The cathode connector and the anode connector are integrally bonded together by metallic bonding. 
     With this busbar, a positive terminal of a battery may be connected to the cathode connector that is made of the same metal as the positive terminal, and a negative terminal of another battery may be connected to the anode connector that is made of the same metal as the negative terminal. Accordingly, galvanic corrosion at the parts connected to the terminals and an increase in electrical resistance due to the galvanic corrosion can be suppressed, and the reliability of the busbar used to connect the batteries can be increased. In addition, the cathode connector and the anode connector of the busbar are integrated together by metallic bonding, and therefore the galvanic corrosion and increase in electrical resistance due to the galvanic corrosion can also be suppressed at the bonding portion. 
     The term “metallic bonding” means that different metals that are to be bonded together form a bonding interface in which they are tightly bonded at the metal structural level so that conductivity and mechanical bonding strength are increased to “values suitable for a busbar in practical use”. 
     Preferably, the cathode connector is formed of aluminum or an aluminum alloy, and the anode connector is formed of copper or a copper alloy. 
     It is essential to manufacture the above-described busbar by a manufacturing method including preparing an opposing base material in which a metal base material that forms the cathode connector is surrounded by a metal base material that forms the anode connector or the metal base material that forms the anode connector is surrounded by the metal base material that forms the cathode connector and subjecting the opposing base material to extrusion or drawing using a die under a high hydrostatic pressure. 
     According to this manufacturing method, a busbar capable of appropriately connecting a positive terminal of a battery to a negative terminal of another battery can be manufactured by integrating the metal material that forms the cathode connector and the metal material that forms the anode connector together by metallic bonding. 
     Advantageous Effects of Invention 
     According to the present invention, a high-performance, high-reliability busbar can be realized which is suitable for use with a battery including a positive terminal and a negative terminal formed of different metals, in which galvanic corrosion can be suppressed and an electrical resistance can be reduced, and which has high mechanical strength. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a perspective view illustrating the manner in which busbars according to a first embodiment is used. 
         FIG. 2A  is a plan view of a busbar according to the first embodiment. 
         FIG. 2B  is a front view of the busbar according to the first embodiment. 
         FIG. 3  is a perspective view illustrating a process of manufacturing busbars according to the present invention. 
         FIG. 4A  is a plan view of a busbar according to a second embodiment. 
         FIG. 4B  is a front view of the busbar according to the second embodiment. 
         FIG. 5  is a perspective view illustrating the manner in which busbars according to a third embodiment is used. 
         FIG. 6A  is a plan view of a busbar according to the third embodiment. 
         FIG. 6B  is a front view of the busbar according to the third embodiment. 
         FIG. 6C  is a perspective view of the busbar according to the third embodiment. 
         FIG. 7  is a perspective view illustrating a process of manufacturing a busbar according to the present invention. 
         FIG. 8A  is a plan view of a busbar according to a fourth embodiment. 
         FIG. 8B  is a front view of the busbar according to the fourth embodiment. 
         FIG. 8C  is a perspective view of the busbar according to the fourth embodiment. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     Embodiments of the present invention will now be described below with reference to the drawings. 
     [First Embodiment] 
       FIGS. 1 to 3  illustrate busbars  1  according to a first embodiment of the present invention. 
       FIG. 1  illustrates an example of how the busbars  1  are used. In an assembled battery  3  including a plurality of battery cells  2  that are connected in series, the busbars  1  are used to connect positive terminals  5  and negative terminals  6  of the battery cells  2  to each other. 
     Each battery cell  2  is a lithium-ion battery. The positive terminal  5  of each battery cell  2  is made of aluminum or an aluminum alloy and has an outer peripheral surface that is externally threaded. The negative terminal  6  of each battery cell  2  is made of copper or a copper alloy and has an outer peripheral surface that is externally threaded. 
     As illustrated in  FIGS. 2A and 2B , each busbar  1  has the shape of an oblong rectangular plate, and is divided into substantially two halves at the middle position in the long-side direction thereof. One of the two halves is a cathode connector  10 , and the other is an anode connector  11 . The dimensions of the busbar  1  may be appropriately set in accordance with, for example, the positions of the two battery cells  2  and the amount of current to be conducted. For example, the length of the long side, the length of the short side, and the thickness may be 30 to 70 mm, 20 to 60 mm, and 1 to 2 mm, respectively. 
     The cathode connector  10  and the anode connector  11  of the busbar  1  are formed of different metals. The cathode connector  10  is formed of the same metal as the positive terminal  5  of each battery cell  2 , that is, aluminum or aluminum alloy. The anode connector  11  is formed of the same metal as the negative terminal  6 , that is, copper or copper alloy. 
     The boundary between the cathode connector  10  and the anode connector  11  of the busbar  1  is formed by placing the metal of the cathode connector  10  (Al) and the metal of the anode connector  11  (Cu) under an ultrahigh pressure (for example, about 1,000 MPa) and causing deformation thereof. The metals are bonded so as to form a bonding interface in which they are tightly bonded at the metal structural level so that the conductivity and mechanical bonding strength are increased to “values suitable for a busbar in practical use”. 
     As illustrated in  FIGS. 2A and 2B , a connection hole  12  that allows the positive terminal  5  of each battery cell  2  to be inserted therethrough is formed in the cathode connector  10  at substantially the central position in the short-side direction thereof. Similarly, a connection hole  13  that allows the negative terminal  6  of each battery cell  2  to be inserted therethrough is formed in the anode connector  11  at substantially the central position in the short-side direction thereof. 
     Referring to  FIG. 1 , each cathode connector  10  is connected to the corresponding positive terminal  5  by inserting the positive terminal  5  through the connection hole  12  and engaging a nut  15  with the positive terminal  5  that projects from the connection hole  12 . Similarly, each anode connector  11  is connected to the corresponding negative terminal  6  by inserting the negative terminal  6  through the connection hole  13  and engaging a nut  15  with the negative terminal  6 . 
     Instead of using the nuts  15 , each cathode connector  10  may be welded to the corresponding positive terminal  5 , and each anode connector  11  may be welded to the corresponding negative terminal  6 . In other words, metal parts of each busbar that are formed of different metals may be directly welded to the respective terminals made of the same metals as the metal parts. 
     Referring to  FIG. 3 , each busbar  1  having the above-described structure is manufactured by extrusion under an ultrahigh hydrostatic pressure. An extruder  20  used in this process includes a die  21  having a single opening whose shape corresponds to a cross sectional shape (planar shape) of the busbar  1  to be manufactured along the long-side direction. The extruder  20  is capable of performing extrusion under an ultrahigh isotropic pressure (for example, about 1,000 MPa). 
     In the process of manufacturing the busbar  1 , first, a cathode base material  10 A (metal base material) made of the same metal as the positive terminal  5  of each battery cell  2  (aluminum or aluminum alloy) and an anode base material  11 A (metal base material) made of the same metal as the negative terminal  6  of each battery cell  2  (copper or copper alloy) are prepared. The cathode base material  10 A and the anode base material  11 A are formed as, for example, section bars, and are bonded together along the longitudinal direction into the form of a round bar-shaped billet (opposing base material). 
     Next, the billet is fed to the extruder  20  so that the cathode base material  10 A and the anode base material  11 A are extruded parallel to each other. 
     In this state, the extruder  20  is operated so as to perform extrusion or drawing under an ultrahigh isotropic pressure, so that a formed body  1 A including the cathode base material  10 A and the anode base material  11 A that are integrated together by metallic bonding is obtained. 
     As illustrated in  FIG. 3 , the opening area of the die  21  of the extruder  20  is smaller than the cross sectional area of the billet. Therefore, when the billet passes through the die  21 , the billet is compressed at the entire periphery thereof and is plastically deformed. The opposing surfaces of the base materials  10 A and  11 A form a bonding interface (metallic bonding portion) between the cathode connector  10  and the anode connector  11  after leaving the die  21 . 
     The formed body  1 A obtained by the above-described process is cut at predetermined intervals in the extruding direction. After the cutting process, the connection hole  12  is formed in the cathode connector  10  and the connection hole  13  is formed in the anode connector  11 . Thus, the busbar  1  is completed. A surface polishing process or a surface treatment process may be performed as necessary. 
     In the busbar  1  that is manufactured by the above-described process, the cathode connector  10  made of the same metal as the positive terminal  5  of each battery cell  2  and the anode connector  11  made of the same metal as the negative terminal  6  of each battery cell  2  are integrated together by metallic bonding. Therefore, galvanic corrosion does not occur at any part of the busbar  1  (including the parts connected to the battery terminals and the bonding surface between the cathode connector  10  and the anode connector  11 ), so that the electrical resistance can be reduced and the mechanical strength can be increased. 
     [Second Embodiment] 
       FIGS. 4A and 4B  illustrate a busbar  1  according to a second embodiment of the present invention. 
     The busbar  1  according to the second embodiment includes a step portion  25  that is crank-shaped in side view at the position where the bonding interface (metallic bonding portion) is formed between the cathode connector  10  and the anode connector  11 . Accordingly, the cathode connector  10  and the anode connector  11  are at different heights. The busbar  1  including the step portion  25  is capable of directly connecting the battery cells  2  that are arranged at different heights (or different positions in the horizontal direction) to each other. 
     The height difference between the cathode connector  10  and the anode connector  11  at the step portion  25  is not restricted in any way. It is not necessary that the step portion  25  be formed at the bonding interface between the cathode connector  10  and the anode connector  11 , and the step portion  25  may instead be formed at a position shifted toward the cathode connector  10  or the anode connector  11 . 
     In addition, the step portion  25  is not necessarily crank-shaped, and may instead be smoothly curved in the shape of the letter ‘S’. 
     Also when the busbar  1  according to the second embodiment is manufactured, extrusion or drawing is performed under an ultrahigh isotropic pressure (about 1,000 MPa or less). In this case, as illustrated in  FIG. 3 , the opening of the die  21  is formed in the crank-shape that corresponds to the cross sectional shape of the busbar  1  along the long-side direction. 
     Other structures, operational effects, and the manufacturing method of the second embodiment are similar to those of the first embodiment, and detailed explanations thereof are thus omitted. 
     EXAMPLE 1 
     A characteristic of a busbar according to the first embodiment manufactured by extrusion or drawing under an ultrahigh isotropic pressure are shown in Table 1. 
     Busbars manufactured by welding using the friction stir method (friction stir welding (FSW)), which is one of manufacturing methods according to the related art, and a busbar manufactured by laser beam welding, which is another one of manufacturing methods according to the related art, are shown as comparative examples. 
     
       
         
               
               
             
           
               
                 TABLE 1 
               
               
                   
               
               
                   
                 Electric Conductivity (% IACS) of Pure Al-Pure Cu 
               
               
                 Bonding Method 
                 Bonded Body 
               
               
                   
               
             
             
               
                 LASER 
                 60.4 
               
               
                 FSW Single 
                 48.5 
               
               
                 FSW Double 
                 49.0 
               
               
                 Present Invention 
                 66.1 
               
               
                   
               
             
          
         
       
     
     As shown in Table 1, the electric conductivities of the busbars formed by friction stir welding were 48.5% (single stirring) and 49.0% (double stirring). Thus, the conductivities were low. The electric conductivity of the busbar formed by laser beam welding was 60.4%, which is higher than those of the busbars formed by friction stir welding. In contrast, the electric conductivity of the busbar according to the first embodiment was 66.1% and was significantly high. Therefore, the busbar according to the first embodiment allows high efficiency power transmission between the battery cells  2  without loss. 
     The embodiments disclosed herein are exemplary and not restrictive in all aspects. The scope of the present invention is defined by the claims and not by the above explanation, and includes equivalents of the claims and all modifications within the scope. 
     For example, the position of the bonding interface (metallic bonding portion) between the cathode connector  10  and the anode connector  11  is not restricted to the center of the busbar  1  in the long-side direction thereof, and may instead be shifted toward the cathode connector  10  or the anode connector  11 . 
     In addition, although the busbars  1  according to the present invention are very suitable for connecting lithium-ion batteries mounted in a vehicle, the busbars  1  may instead be used to connect lithium-ion batteries for other uses. 
     [Third Embodiment] 
       FIGS. 5 to 7  illustrate busbars  101  according to a third embodiment of the present invention. 
       FIG. 5  illustrates an example of how the busbars  101  are used. In an assembled battery  103  including a plurality of battery cells  102  that are connected in series, the busbars  101  are used to connect positive terminals  105  and negative terminals  106  of the battery cells  102  to each other. 
     Each battery cell  102  is a lithium-ion battery. The positive terminal  105  of each battery cell  102  is made of aluminum or an aluminum alloy and has an outer peripheral surface that is externally threaded. The negative terminal  106  of each battery cell  102  is made of copper or a copper alloy and has an outer peripheral surface that is externally threaded. 
     As illustrated in  FIGS. 6A to 6C , each busbar  101  has the shape of an oblong rectangular plate, and is divided into substantially two halves at the middle position in the long-side direction thereof. One of the two halves is a cathode connector  110 , and the other is an anode connector  111 . In the present embodiment, the cathode connector  110  includes a frame portion  114  that extends to the anode-connector- 111  side, and the anode connector  111  is fitted in the frame portion  114 . In other words, the entire periphery of the anode connector  111  is surrounded by the cathode connector  110 . 
     The dimensions of the busbar  101  may be appropriately set in accordance with, for example, the positions of the two battery cells  102  and the amount of current to be conducted. For example, the length of the long side, the length of the short side, and the thickness may be 30 to 70 mm, 20 to 60 mm, and 1 to 2 mm, respectively. 
     The cathode connector  110  and the anode connector  111  of the busbar  101  are formed of different metals. The cathode connector  110  is formed of the same metal as the positive terminal  105  of each battery cell  102 , that is, aluminum or aluminum alloy. The anode connector  111  is formed of the same metal as the negative terminal  106 , that is, copper or copper alloy. 
     The cathode connector  110  and the anode connector  111  are integrally bonded together by metallic bonding at the bonding surface along the inner periphery of the frame portion  114 . The bonding surface (boundary surface) is formed by placing the metal of the cathode connector  110  (Al) and the metal of the anode connector  111  (Cu) under an ultrahigh pressure (for example, about 1,000 MPa) and causing deformation thereof. The metals are bonded so as to form a bonding interface in which they are tightly bonded at the metal structural level so that the conductivity and mechanical bonding strength are increased to “values suitable for a busbar in practical use”. 
     Referring to  FIGS. 6A to 6C , since aluminum or aluminum alloy which forms the cathode connector  110  is softer than copper or copper alloy which forms the anode connector  111 , the cathode connector  110  is formed so as to swell toward the anode connector  111  in the extrusion of the metals under an ultrahigh hydrostatic pressure. Therefore, the anode connector  111  is formed so as to be recessed in plan view in the present embodiment. 
     As illustrated in  FIGS. 6A to 6C , a connection hole  112  that allows the positive terminal  105  of each battery cell  102  to be inserted therethrough is formed in the cathode connector  110  at substantially the central position in the short-side direction thereof. Similarly, a connection hole  113  that allows the negative terminal  106  each battery cell  102  to be inserted therethrough is formed in the anode connector  111  at substantially the central position in the short-side direction thereof. 
     Referring to  FIG. 5 , each cathode connector  110  is connected to the corresponding positive terminal  105  by inserting the positive terminal  105  through the connection hole  112  and engaging a nut  115  with the positive terminal  105  that projects from the connection hole  112 . Similarly, each anode connector  111  is connected to the corresponding negative terminal  106  by inserting the negative terminal  106  through the connection hole  113  and engaging a nut  115  with the negative terminal  106 . 
     Instead of using the nuts  115 , each cathode connector  110  may be welded to the corresponding positive terminal  105 , and each anode connector  111  may be welded to the corresponding negative terminal  106 . In other words, metal parts of each busbar that are formed of different metals may be directly welded to the respective terminals made of the same metals as the metal parts. 
     Referring to  FIG. 7 , each busbar  101  having the above-described structure is manufactured by extrusion under an ultrahigh hydrostatic pressure. An extruder  120  used in this process includes a die  121  having a single opening whose shape corresponds to a cross sectional shape (planar shape) of the busbar  101  to be manufactured along the long-side direction. The extruder  120  is capable of performing extrusion under an ultrahigh isotropic pressure (for example, about 1,000 MPa). 
     In the process of manufacturing the busbar  101 , first, a section-bar shaped cathode base material  110 A (metal base material) made of the same metal as the positive terminal  105  of each battery cell  102  (aluminum or aluminum alloy) and a section-bar shaped anode base material  111 A (metal base material) made of the same metal as the negative terminal  106  of each battery cell  102  (copper or copper alloy) are prepared. Next, the section-bar shaped cathode base material  110 A and anode base material  111 A are bonded together along the longitudinal direction to form a bonded member, and the outer periphery of the bonded member is wrapped by a plate-shaped cathode base material  110 A. Thus, a round-bar shaped billet (opposing base material) is prepared. The billet may instead be formed by fitting the bonded member formed by bonding the cathode base material  110 A and the anode base material  111 A together into a hollow-pipe-shaped cathode base material  110 A. 
     Next, the billet is fed to the extruder  120  so that the cathode base material  110 A and the anode base material  111 A are extruded parallel to each other. 
     In this state, the extruder  120  is operated so as to perform extrusion or drawing under an ultrahigh isotropic pressure, so that a formed body  101 A including the cathode base material  110 A and the anode base material  111 A that are integrated together by metallic bonding is obtained. 
     As illustrated in  FIG. 7 , the opening area of the die  121  of the extruder  120  is smaller than the cross sectional area of the billet. Therefore, when the billet passes through the die  121 , the billet is compressed at the entire periphery thereof and is plastically deformed. The opposing surfaces of the base materials  110 A and  111 A form a bonding interface (metallic bonding portion) between the cathode connector  110  and the anode connector  111  after leaving the die  121 . 
     The formed body  101 A obtained by the above-described process is cut at predetermined intervals in the extruding direction. After the cutting process, the connection hole  112  is formed in the cathode connector  110  and the connection hole  113  is formed in the anode connector  111 . Thus, the busbar  101  is completed. A surface polishing process or a surface treatment process may be performed as necessary. 
     In the busbar  101  that is manufactured by the above-described process, the cathode connector  110  made of the same metal as the positive terminal  105  of each battery cell  102  and the anode connector  111  made of the same metal as the negative terminal  106  of each battery cell  102  are integrated together by metallic bonding. Therefore, galvanic corrosion does not occur at any part of the busbar  101  (including the parts connected to the battery terminals and the bonding surface between the cathode connector  110  and the anode connector  111 ), so that the electrical resistance can be reduced and the mechanical strength can be increased. 
     [Fourth Embodiment] 
       FIGS. 8A to 8C  illustrate a busbar  101  according to a fourth embodiment of the present invention. 
     The busbar  101  of the fourth embodiment also has the shape of an oblong rectangular plate, and is divided into substantially two halves at the middle position in the long-side direction thereof. One of the two halves is a cathode connector  110  (Al), and the other is an anode connector  111  (Cu). 
     In the present embodiment, the anode connector  111  includes a frame portion  114  that extends to the cathode-connector- 110  side, and the cathode connector  110  is fitted in the frame portion  114 . In other words, the entire periphery of the cathode connector  110  is surrounded by the anode connector  111 . 
     Referring to  FIGS. 8A to 8C , since aluminum or aluminum alloy which forms the cathode connector  110  is softer than copper or copper alloy which forms the anode connector  111 , the cathode connector  110  is formed so as to swell toward the anode connector  111  in the extrusion of the metals under an ultrahigh hydrostatic pressure. Therefore, the cathode connector  110  is formed so as to swell outward in plan view in the present embodiment. 
     Other structures, operational effects, and the manufacturing method of the fourth embodiment are similar to those of the third embodiment, and detailed explanations thereof are thus omitted. 
     The embodiments disclosed herein are exemplary and not restrictive in all aspects. The scope of the present invention is defined by the claims and not by the above explanation, and includes equivalents of the claims and all modifications within the scope. 
     For example, the length and width of the frame portion  114  are not limited. In addition, the ratio between the areas of the cathode connector  110  and the anode connector  111  in plan view may be changed as appropriate. 
     In addition, although the busbars  101  according to the present invention are very suitable for connecting lithium-ion batteries mounted in a vehicle, the busbars  101  may instead be used to connect lithium-ion batteries for other uses. 
     Although the present application has been described in detail with reference to specific embodiments, various alterations and modifications are possible within the spirit and scope of the present invention. 
     This application is based on Japanese Patent Application filed Mar. 29, 2010 (Japanese Patent Application No. 2010-075915) and Japanese Patent Application filed Mar. 29, 2010 (Japanese Patent Application No. 2010-075917), the contents of which are incorporated herein by reference. 
     
       
         
               
             
               
               
               
             
           
               
                   
               
               
                 Reference Signs List 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                   
                  1 
                 busbar 
               
               
                   
                  1A  
                 formed body 
               
               
                   
                  2 
                 cell 
               
               
                   
                  3 
                 assembled battery 
               
               
                   
                  5  
                 cathode terminal 
               
               
                   
                  6 
                 anode terminal 
               
               
                   
                  10 
                 cathode connector 
               
               
                   
                  10A 
                 cathode base material 
               
               
                   
                  11 
                 anode connector 
               
               
                   
                  11A 
                 anode base material 
               
               
                   
                  12 
                 connection hole 
               
               
                   
                  13 
                 connection hole 
               
               
                   
                  15 
                 nut 
               
               
                   
                  20 
                 extruder 
               
               
                   
                  21 
                 die 
               
               
                   
                  25 
                 step portion 
               
               
                   
                 101 
                 busbar 
               
               
                   
                 101A 
                 formed body 
               
               
                   
                 102 
                 cell 
               
               
                   
                 103 
                 assembled battery 
               
               
                   
                 105 
                 cathode terminal 
               
               
                   
                 106 
                 anode terminal 
               
               
                   
                 110 
                 cathode connector 
               
               
                   
                 110A 
                 cathode base material 
               
               
                   
                 111 
                 anode connector 
               
               
                   
                 111A 
                 anode base material 
               
               
                   
                 112 
                 connection hole 
               
               
                   
                 113 
                 connection hole 
               
               
                   
                 114 
                 frame portion 
               
               
                   
                 115 
                 nut 
               
               
                   
                 120 
                 extruder 
               
               
                   
                 121 
                 die 
               
               
                   
                 125 
                 step portion