Abstract:
A battery module including a plurality of rechargeable batteries, and a connector for connecting a first terminal of one of the plurality of rechargeable batteries and including a first material to a second terminal of another one of the plurality of rechargeable batteries and including a second material, wherein the connector includes: a first portion connected to the first terminal and including the first material; and a second portion connected to the second terminal and including the second material, and a welded portion connecting the first portion and the second portion.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of U.S. Provisional Application No. 61/248,806, filed on Oct. 5, 2009, in the United States Patent and Trademark Office, the disclosure of which is incorporated herein in its entirety by reference. 
    
    
     BACKGROUND 
     1. Field 
     The following description relates to a battery module with electrically connected rechargeable batteries. 
     2. Description of Related Art 
     Rechargeable batteries can be charged and discharged. Small capacity rechargeable batteries are used for small portable electronic devices such as mobile phones, laptop computers, and camcorders, while large capacity batteries are used as power sources for driving motors of hybrid vehicles, etc. 
     High power battery modules using a high energy density non-aqueous electrolyte have been developed, and the high power battery modules are formed as large-capacity battery modules by connecting a plurality of rechargeable batteries in series to be used for driving the motors of electric vehicles, etc. 
     Further, one large capacity rechargeable battery is generally composed of a plurality of rechargeable batteries connected in series, in which the rechargeable battery may be formed in a cylindrical shape or a prismatic shape. 
     Prismatic rechargeable batteries include a case having an electrode assembly in which a positive electrode and a negative electrode are disposed with a separator therebetween, and a space where the electrode assembly is disposed, a cap plate sealing the case and having a terminal hole where an electrode terminal is inserted, and an electrode terminal that is electrically connected with the electrode assembly and protrudes outside the case through the terminal hole. 
     The electrode terminal is fixed to the cap plate by a nut, but the nut can be loosened by continuous external vibration or shock. This causes contact resistance inside the rechargeable batteries, such that the output and cycle-life of the rechargeable batteries are reduced. 
     In particular, when a positive electrode terminal is made of aluminum and a negative electrode terminal is made of copper, since a connecting member and at least one of the positive electrode terminal or the negative electrode terminal are made of different materials, corrosion may occur or contact resistance may be continuously increased by contact between the different metals. 
     A method of connecting a connecting member to the positive electrode and the negative electrode using resistance welding has been proposed. 
     However, when the connecting member is made of a different material from that of at least one of the positive electrode terminal or the negative electrode terminal, it is difficult to bond the connecting member and the terminals with different materials using resistance welding or ultrasonic welding because of the different melting points. 
     The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art. 
     SUMMARY OF THE INVENTION 
     Exemplary embodiments of the present invention provide a battery module for easily and stably connecting a connecting member with terminals. 
     A battery module according to an exemplary embodiment of the present invention includes: a plurality of rechargeable batteries, and a connector for connecting a first terminal of one of the plurality of rechargeable batteries and including a first material to a second terminal of another one of the plurality of rechargeable batteries and including a second material, wherein the connector includes: a first portion connected to the first terminal and including the first material; and a second portion connected to the second terminal and including the second material, and a welded portion connecting the first portion and the second portion. 
     The welded portions may be formed by friction stir welding. 
     The welded portion may include a spot weld. 
     The first material may include aluminum. The second material may include copper. The first material and the second material may be different. 
     The first portion may include a first connecting bar and a first protrusion extending from the first connecting bar. The second portion may include a second connecting bar and a second protrusion extending from the second connecting bar, wherein the first protrusion and the second protrusion are configured to overlap with one another to form an overlapping region, and wherein the overlapping region includes the welded portion. The first protrusion may be thinner than the first connecting bar and the second protrusion may be thinner than the second connecting bar, wherein the first connecting bar, the second connecting bar, and the overlapping region may have substantially a same thickness. The first portion and the second portion may be plate shaped, wherein the first protrusion is a bended portion formed in a plane parallel to a plane of the first connecting bar, wherein the bended portion overlaps with part of the second portion to form an overlapping region, and wherein the overlapping region includes the welded portion. The first connecting bar and the second connecting bar may be coplanar, wherein the connector is thicker at the overlapping region than at the first connecting bar or at the second portion. 
     The first portion and the second portion may be plate shaped and are arranged to be coplanar, wherein a side of the first portion and a side of the second portion may be in contact with one another. The welded portion may be formed in a line where the side of the first portion and the side of the second portion are in contact. 
     The first terminal and the second terminal may be plate shaped, wherein the first portion is welded to the first terminal and the second portion is welded to the second terminal. 
     The first terminal and the second terminal may be cylindrical and include threaded exterior surfaces, wherein the first portion and the second portion of the connector each has a terminal hole for respectively accommodating the first terminal and the second terminal, and wherein locking nuts connect the connector to the first terminal and the second terminal, respectively. 
     The welded portion may include a nugget zone including a mixture of the first material and the second material. The first portion and the second portion of the connector may be in contact, and wherein the nugget zone traverses the contacting surfaces of the first portion and the second portion. The nugget zone may be formed by melding of the first portion with the second portion while in a solid state to form a melded material, and a dynamic recrystallization of the melded material. The welded portion may further include a thermo-mechanically affected zone around the nugget zone and formed by plastic deformation and partial recrystallization of the first material with the second material, and a heat affected zone around the thermo-mechanically affected zone and having slanting crystals and air holes. 
     The welded portion may include a welding groove recessed from a surface of the connector. 
     According to another exemplary embodiment of the present invention, a method of connecting a first terminal of a first rechargeable battery with a second terminal of a second rechargeable battery, includes: providing a first connector portion including a same material as the first terminal; providing a second connector portion including a same material as the second terminal; and forming a welded portion to connect the first connector portion with the second connector portion by utilizing friction stir welding; and connecting the first connector portion to the first terminal and the second connector portion to the second terminal. 
     The friction stir welding may form a nugget zone including a mixture of the first material and the second material by melding of the first connector portion with the second connector portion while in a solid state to form a melded material, and dynamic recrystallization of the melded material. 
     According to exemplary embodiments of the present invention, with a decrease in contact resistance and corrosion, the output of the battery module can be improved, and the cycle-life of the battery module can also be improved. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view showing a battery module according to a first exemplary embodiment of the present invention; 
         FIG. 2  is a perspective view of a connecting member according to the first exemplary embodiment of the present invention; 
         FIG. 3  is a partial cross-sectional view of the connecting member according to the first exemplary embodiment of the present invention; 
         FIG. 4  is a perspective view showing a connecting member according to a second exemplary embodiment of the present invention; 
         FIG. 5  is a perspective view showing a connecting member according to a third exemplary embodiment of the present invention; and 
         FIG. 6  is a perspective view showing a battery module according to a fourth exemplary embodiment of the present invention. 
     
    
    
     DESCRIPTION OF REFERENCE NUMERALS INDICATING FEATURES IN THE DRAWINGS 
     
       
         
               
               
             
           
               
                   
               
             
             
               
                 100, 300: battery module 
                 110, 310: rechargeable battery 
               
               
                 112, 312: case 
                 114, 314: cap plate 
               
               
                 130, 330: positive electrode  
                 140, 340: negative electrode terminal 
               
               
                 terminal 
                   
               
               
                 150, 215, 236: welded portion 
                 151, 216, 235: welding groove 
               
               
                 152: nugget zone 
                 154: thermo-mechanically affected zone 
               
               
                 156: heat affected zone 
                 160, 210, 230, 350: connecting member 
               
               
                 161, 211, 231, 351: first  
                 211a: body portion 
               
               
                 connecting bar 
                   
               
               
                 212a: bended portion 
                 161a: first welding protrusion 
               
               
                 162, 212, 232, 352: second  
                 323: lower nut 
               
               
                 connecting bar 
                   
               
               
                 162a: second welding protrusion 
                 351a, 352a: terminal hole 
               
               
                 165: terminal welded portion 
                   
               
               
                 324: upper nut 
               
               
                   
               
             
          
         
       
     
     DETAILED DESCRIPTION 
     In the following detailed description, only certain exemplary embodiments of the present invention have been shown and described by way of illustration. As those skilled in the art will recognize, the described embodiments may be modified in various different ways without departing from the spirit or scope of the present invention. Accordingly, the drawings and description are to be regarded as illustrative in nature and not restrictive. Like reference numerals designate like elements throughout the specification. 
       FIG. 1  is a perspective view showing a battery module according to a first exemplary embodiment of the present invention, and  FIG. 2  is a perspective view showing a connecting member according to the first exemplary embodiment of the present invention. 
     Referring to  FIG. 1  and  FIG. 2 , a battery module  100  according to the first exemplary embodiment includes a plurality of rechargeable batteries  110  each having a positive electrode terminal  130  and a negative electrode terminal  140 , and connecting members  160  that electrically connect the rechargeable batteries  110 . 
     The battery module  100  according to the first exemplary embodiment is formed by connecting the rechargeable batteries  110  in series. However, the present invention is not limited thereto, and in some embodiments the rechargeable batteries  110  may be connected, for example, in parallel. 
     The rechargeable battery  110  according to the first exemplary embodiment is formed in a prismatic shape and includes a case  112 , a cap plate  114  connected to an opening of the case  112 , and the positive electrode terminal  130  and the negative electrode terminal  140  that protrude outside the case  112 . Although the rechargeable battery is exemplified in the first exemplary embodiment in a prismatic shape, the present invention is not limited thereto, and the battery may be formed, for example, in a cylindrical shape or other shapes. 
     A vent member  116  that is opened when an internal pressure increases and a sealing cap  118  for sealing an electrolyte injection inlet are located on the cap plate  114 . 
     The terminals  130  and  140  are fixed to the cap plate  114  while protruding outside the cap plate  114 , and a gasket  123  is positioned between the cap plate  114  and each of the terminals  130  and  140  for insulation and sealing. In this embodiment, the positive electrode terminal  130  and the negative electrode terminal  140  are formed substantially in a plate shape and are electrically connected to an electrode assembly (not shown) inserted in the case  112 . The positive electrode terminal  130  may be made of aluminum and the negative electrode terminal  140  may be made of copper. 
     The rechargeable batteries  110  are arranged to be adjacent to each other and are connected in series by the connecting members  160 , in which the positive electrode terminals  130  and the negative electrode terminals  140  of adjacent rechargeable batteries  110  are alternately arranged, and the connecting member  160  is welded to the positive electrode terminal  130  of one rechargeable battery  110  and the negative electrode terminal of an adjacent rechargeable battery  110 . 
     The connecting member  160  is plate shaped and covers the positive electrode terminal  130  and the negative electrode terminal  140 . The connecting member  160  is welded to the terminals  130  and  140 , respectively, and a terminal welded portion  165  is formed on the connecting member  160 . 
     The connecting member  160  includes a first connecting bar  161  and a second connecting bar  162  that is bonded to the first connecting bar  161  by friction stir welding. The first connecting bar  161  may be made of aluminum, as may be the positive electrode terminal  130 , and the second connecting bar  162  may be made of copper, as may be the negative electrode terminal  140 . The first connecting bar  161  is fixed to the positive electrode terminal  130 , for example, by welding and the second connecting bar  162  is fixed to the negative electrode terminal  140 , for example, by welding. 
     A first welding protrusion  161   a  is formed at a side of the first connecting bar  161 . The first welding protrusion  161   a  may extend from a lower side of the first connecting bar  161  and may have a smaller thickness than other portions of the first connecting bar  161 , and is stepped with respect to an upper surface of the first connecting bar  161 . 
     A second welding protrusion  162   a  is formed at a side of the second connecting bar  162 . The second welding protrusion  162   a  may extend from a lower side of the second connecting bar  162  and may have a smaller thickness than other portions of the second connecting bar  162 , and is stepped with respect to an upper surface of the second connecting bar  162 . 
     The second welding protrusion  162   a  is positioned over the first welding protrusion  161   a , such that the second welding protrusion  162   a  overlaps with the first welding protrusion  161   a . In this position, the first welding protrusion  161   a  and the second welding protrusion  162   a  are bonded by friction stir welding. 
       FIG. 3  is a partial cross-sectional view of a connecting portion according to the first exemplary embodiment of the present invention. 
     Referring to  FIG. 3 , with the welding protrusions  161   a  and  162   a  overlapping, a welded portion  150  is formed by rotating a tool to recrystallize the structure using dynamic flow. The tool has a pin and a shank where the pin is fixed, and the cross-section where the pin protrudes from the shank is called a shoulder. 
     The first connecting bar  161  and the second connecting bar  162  may be bonded by spot welding, in which the portion where the shoulder contacts the connecting member  160  is the welded portion  150 , and a welding groove  151  is located around a portion of the welded portion  150  where the pin was positioned. 
     As shown in  FIG. 3 , a nugget zone  152  that is formed by dynamic recrystallization, a thermo-mechanically affected zone (TMAZ)  154 , and a heat affected zone (HAZ)  156  are formed in the welded portion  150 . 
     The nugget zone  152  is a portion where recovery and recrystallization occur due to high heat and the amount of deformation, such that the nugget zone  152  may also be called a dynamic-recrystallized portion. Unlike general welding in which melting occurs by heat, the nugget zone  152  is formed by dynamic recrystallization of materials that are melded in a solid state by friction heat and stirring. A diameter of the nugget zone  152  is generally larger than a diameter of the pin and smaller than a diameter of the shoulder  183 . The size of the nugget zone  152  varies based on the rotational speed of the tool, such that when the rotational speed is high, the size of the nugget zone  152  is reduced. When the rotational speed is too high, the shape of the crystals may be incomplete, and defects may occur approximate the incomplete portion. 
     The thermo-mechanically affected zone  154  is a portion where partial recrystallization occurs by plastic deformation caused by friction at a contact surface where the shoulder of the tool contacts the connecting member  160 , and where thermal deformation by friction and mechanical deformation caused by the shoulder simultaneously occur. Crystals softened by excessive plastic flow and deformation of the material are distributed at an angle in the thermo-mechanically affected zone  154 . 
     The heat affected zone  156  is more affected by heat than the thermo-mechanically affected zone  154 , in which slanting crystals exist and a plurality of air holes may be formed. 
     When the first connecting bar  161  contacting the positive electrode terminal  130  is made of the same material as the positive electrode terminal  130  and the second connecting bar  162  contacting the negative electrode terminal  140  is made of the same material as the negative electrode terminal  140 , as in the present exemplary embodiment, contact resistance may be minimized or reduced, and corrosion between the connecting member  160  and the terminals  130  and  140  may also be minimized or reduced. Accordingly, not only will the output of the battery module  100  be improved, but bonding between the connecting member  160  and the terminals  130  and  140  is also improved, such that the overall cycle-life of the battery module  100  may also be improved. 
     Further, in the connecting member  160 , the portion made of the same material as the positive electrode terminal  130  is welded to the positive electrode terminal  130 , and the portion made of the same material as the negative electrode terminal  140  is welded to the negative electrode terminal  140 , such that respective weldability between the connecting member  160  and terminals  130  and  140  is improved. 
     Further, by bonding the first connecting bar  161  and the second connecting bar  162  by friction stir welding, the first connecting bar  161  made of aluminum and the second connecting bar  162  made of copper may be more effectively welded together. Copper and aluminum have different melting points, such that when they are bonded by resistance welding or ultrasonic welding there is a greater possibility that defects may occur at the welded portion  150 , or the welded portion may more easily be separated by external shock or vibration. In particular, when a battery module is used in electric vehicles or hybrid electric vehicles, vibration is continuously applied to the connecting member  160 , such that the continuous vibration may cause contact defects between the connecting member and the terminals. 
     However, when the first connecting bar  161  and the second connecting bar  162  are bonded by friction stir welding, as in the present exemplary embodiment, solid-state bonding can be achieved, such that the connecting member  160  and the terminals  130  and  140 , which have different melting points, can be stably bonded together. In particular, the nugget zone  152  formed approximate the center of the welded portion  150  is an area where dynamic recrystallization occurs, such that it has a structure that more effectively resists external vibration and shock. Further, the thermo-mechanically affected zone  154 , which is an area where two connecting bars  161  and  162  are rotated and bonded, has mixed parent metals, such that it also has structural characteristics that resist external shock and vibration. 
     Further, the friction stir welding does not need a heat source, a welding rod, or a filler metal, unlike other types of welding, such that friction stir welding is a more environmentally-friendly type of welding that does not discharge harmful light or substances. Further, since dynamic recombination occurs, solidification cracks that may occur in, for example, fuse bonding, may be minimized or reduced and there is less deformation, such that mechanical properties are excellent. 
       FIG. 4  is a perspective view showing a connecting member according to a second exemplary embodiment of the present invention. 
     Referring to  FIG. 4 , a connecting member  210  according to the second exemplary embodiment includes a first connecting bar  211  and a second connecting bar  212  attached to the first connecting bar  211 , for example, by welding. The first connecting bar  211  and the second connecting bar  212  are made of different materials, in which the first connecting bar  211  may be made of the same material as the negative electrode terminal  140  and the second connecting bar  212  may be made of the same material as the positive electrode terminal  130 . 
     The second connecting bar  212  is formed substantially in a rectangular plate shape. The first connecting bar  211  has a body portion  211   a  arranged in substantially a same plane with the second connecting bar  212 , and a bended portion  212   a  bending from the body portion  211   a  and arranged to be under the second connecting bar  212  in a plane substantially parallel to the body portion  211   a.    
     The bended portion  212   a  is in close contact with the lower side of the second connecting bar  212  and overlaps the second connecting bar  212 . A welded portion  215  is formed by bonding the second connecting bar  212  and the bended portion  212   a  by friction stir welding using a tool. A welding groove  216  where a pin of the tool was positioned is located around the center of the welded portion  215 . 
     The first connecting bar  211  can easily overlap with the second connecting bar  212  by bending the first connecting bar  211  according to the second exemplary embodiment. Further, since the first connecting bar  211  and the second connecting bar  212  are bonded by friction stir welding, different metals can be more easily and stably bonded together, and the connecting member  210  can also be more easily coupled to the terminals  130  and  140 , for example, by more conventional types of welding. 
       FIG. 5  is a perspective view showing a connecting member according to a third exemplary embodiment of the present invention. 
     Referring to  FIG. 5 , a connecting member  230  according to the third exemplary embodiment includes a first connecting bar  231  and a second connecting bar  232  attached to the first connecting bar  231  by, for example, welding. The first connecting bar  231  and the second connecting bar  232  may be made of different materials, in which the first connecting bar  231  may be made of the same material as the positive electrode terminal  130  and the second connecting bar  232  may be made of the same material as the negative electrode terminal  140 . 
     The first connecting bar  231  and the second connecting bar  232  are each formed substantially in a rectangular plate shape and arranged such that a side of the first connecting bar  231  and a side of the second connecting bar  232  contact each other. 
     In this position, a tool is positioned at an interface between the first connecting bar  231  and the second connecting bar  232 , and the first connecting bar  231  and the second connecting bar  232  can be fixed together by welding. The tool performs welding while moving along the interface between the first connecting bar  231  and the second connecting bar  232 , such that a welded portion  236  is shaped substantially in a line. A welding groove  235  where the pin was positioned is located around a center of the welded portion  236 . 
     According to the third exemplary embodiment, since a weld line is formed with the first connecting bar  231  and the second connecting bar  232  contacting each other, the welded area is wider such that the first connecting bar  231  and the second connecting bar  232  can be more stably fixed. 
       FIG. 6  is a perspective view showing a battery module according to a fourth exemplary embodiment of the present invention. 
     Referring to  FIG. 6 , a battery module  300  according to the fourth exemplary embodiment includes a plurality of rechargeable batteries  310  having a positive electrode terminal  330  and a negative electrode terminal  340 , and connecting members  350  that electrically connect the rechargeable batteries  310 . 
     The battery module  300  according to the third exemplary embodiment is formed by connecting the rechargeable batteries  310  in series. 
     The rechargeable batteries  310  according to the fourth exemplary embodiment are each formed in a prismatic shape and include a case  312 , a cap plate  314  connected to an opening of the case  312 , and the positive electrode terminal  330  and the negative electrode terminal  340  protruding outside the case  312 . A vent member  316  that is opened when an internal pressure increases and a sealing cap  318  for sealing an electrolyte injection inlet are located on the cap plate  314 . 
     Further, the terminals  330  and  340  protrude outside the cap plate  314 , and lower nuts  323  for supporting the terminals  330  and  340  on the cap plate  314  are fitted on the terminals  330  and  340 . Further, a gasket  321  may be arranged between each lower nut  323  and the cap plate  314  for insulation. 
     In this embodiment, the positive electrode terminal  330  and the negative electrode terminal  340  are each substantially in a cylindrical shape, and the outer circumferential surfaces may be threaded to fit nuts. Further, the positive electrode terminal  330  and the negative electrode terminal  340  of each battery are electrically connected with an electrode assembly inserted in the case  312  of the battery. The positive electrode terminal  330  may be made of aluminum and the negative electrode terminal  340  may be made of copper. 
     The connecting member  350  is arranged on the lower nuts  323 , and includes a first connecting bar  351  contacting the positive electrode terminal  330  and a second connecting bar  352  contacting the negative electrode terminal  340 . The first connecting bar  351  may be made of the same material as the positive electrode terminal  330 , and may have a terminal hole  351   a  in which the positive electrode terminal  330  is inserted. The second connecting bar  352  may be made of the same material as the negative electrode terminal  340 , and may have a terminal hole  352   a  in which the negative electrode terminal  340  is inserted. 
     The connecting member  350  can be fixed to the terminals  330  and  340  by inserting the positive electrode terminal  330  and the negative electrode terminal  340  in the terminal holes  351   a  and  352   a , respectively, and then respectively fitting upper nuts  324  on the terminals  330  and  340 . 
     In some embodiments, the connecting member  350  is formed in a similar structure as the connecting member  160  according to the first exemplary embodiment. Welding protrusions are formed on the first connecting bar  351  and the second connecting bar  352 , and a welded portion  360  is formed on the connecting portion by overlapping and then bonding the welding protrusions using friction stir welding. In other embodiments, the connecting member may have other structures, for example, similar to the connecting members as described above in the second or third embodiments. 
     According to the fourth exemplary embodiment, if the portion of the connecting member  350  contacting the positive electrode terminal  330  is made of the same material as the positive electrode terminal  330 , and the portion of the connecting member  350  contacting the negative electrode terminal  340  is made of the same material as the negative electrode terminal  340 , corrosion between the connecting member  350  and the terminals  330  and  340  can be minimized or reduced. Further, since the first connecting bar  351  and the second connecting bar  352  are bonded by friction stir welding, different metals can be more stably fixed together. 
     While this invention has been described in connection with what is presently considered to be practical exemplary embodiments, it is to be understood that the invention is not limited to the disclosed embodiments, but is instead intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims.