Abstract:
A rechargeable battery includes an electrode group in a case, the electrode group including a first electrode and a second electrode, a cap plate coupled to the case, an electrode terminal electrically connected to the first electrode, the electrode terminal being electrically insulated from the cap plate, and a current interrupt device (CID) electrically connected to the second electrode and the cap plate, the CID including a membrane on a first surface of the cap plate, the membrane being between and electrically connecting the second electrode and the cap plate, and the membrane being configured to interrupt the electrical connection when a voltage greater than a setting voltage is charged, a first insulator contacting the first surface of the cap plate and at least one surface of the membrane to support the membrane, and a fastening member connecting the cap plate and the first insulator.

Description:
BACKGROUND 
       [0001]    1. Field 
         [0002]    The described technology relates to a rechargeable battery and a module thereof. More particularly, the described technology relates to a rechargeable battery and a module thereof that reduce resistance of a current interrupt device and improve durability of a current interrupt device during vibration or impact. 
         [0003]    2. Description of the Related Art 
         [0004]    A conventional rechargeable battery may include a current interrupt device (CID) that interrupts current upon overcharging. However, because the CID has a complex structure and many parts, it may be difficult to apply a conventional CID, e.g., a CID used in a small battery, to a large square-shaped rechargeable battery that uses a high current, e.g., in a hybrid electric vehicle (HEV). 
         [0005]    Further, when a large resistance is formed in the CID, a temperature thereof may increase due to high current. Therefore, it may be difficult to apply the conventional CID to a rechargeable battery for driving a motor requiring a large amount of power. 
         [0006]    It is necessary for CIDs that are used for a rechargeable battery for a hybrid electric vehicle (HEV), a plug-in hybrid electric vehicle (PHEV), or an electric vehicle to have strong durability to vibration or impact of the vehicle. 
         [0007]    The above information disclosed in this Background section is only for enhancement of understanding of the background of the described technology 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 
       [0008]    Embodiments are therefore directed to a rechargeable battery and a module thereof, which substantially overcome one or more of the problems due to the limitations and disadvantages of the related art. 
         [0009]    It is therefore a feature of an embodiment to provide a rechargeable battery and a module thereof having a CID of a simple structure in order to prevent overcharge and secure safety. 
         [0010]    It is therefore another feature of an embodiment to provide a rechargeable battery and a module thereof having a CID structure adapted to have reduced resistance, thereby improving durability of the CID during vibration or impact. 
         [0011]    At least one of the above and other features and advantages may be realized by providing a rechargeable battery, including a case that houses an electrode group including a first electrode and a second electrode, a cap plate that is coupled to the case, an electrode terminal that is electrically insulated from the cap plate and electrically connected to the first electrode to be protruded to a first surface of the cap plate, and a CID that electrically connects the second electrode and the cap plate and that interrupts an electrical connection when a voltage greater than a setting voltage is charged. The CID may include a membrane that is disposed at a second surface that is formed at an opposite side of the first surface of the cap plate to electrically connect the second electrode and the cap plate, and that interrupts an electrical connection when a voltage greater than a setting voltage is charged, a first insulator that contacts the second surface of the cap plate and at least one surface of the membrane to support the membrane, and a fastening member that fastens the cap plate and the first insulator. 
         [0012]    The CID may further include a first middle plate that is disposed at a surface of an opposite side of the cap plate of the first insulator, and that is connected to the second electrode by a lead tab and has a first penetration hole corresponding to the membrane, and the membrane may include a first flange that is disposed between the second surface of the cap plate and the first middle plate, and a first welding part that is convexly formed toward the first middle plate in the first flange to be electrically connected to the first middle plate. 
         [0013]    The fastening member may include a first rivet and a second rivet that fasten the cap plate, the first insulator, and the first middle plate. 
         [0014]    The membrane may include a first flange that is connected to the second surface of the cap plate, and a first welding part that is convexly formed toward an opposite side of the cap plate in the first flange, and the CID may further include a sub-plate including a second welding part that is electrically connected to the second electrode to be convexly formed toward the membrane, and wherein the first welding part and the second welding part may be welded to each other. 
         [0015]    The CID may further include a first middle plate that is disposed at a surface of an opposite side of the cap plate of the first insulator, that is connected to the second electrode by a lead tab, and that includes a first penetration hole corresponding to the membrane, the sub-plate may include a second flange that is integrally formed with the second welding part and that is connected to a surface of an opposite side of the first insulator of the first middle plate, and the second welding part may pass through the first penetration hole and be welded to the first welding part. 
         [0016]    The fastening member may include a first rivet and a second rivet that fasten the cap plate, the first insulator, and the first middle plate. 
         [0017]    The cap plate may have a second penetration hole corresponding to the first penetration hole. 
         [0018]    The membrane may include a fracture part that is inverted into the second penetration hole to function as a vent. 
         [0019]    The electrode terminal may be disposed by interposing the second insulator at the second surface of the cap plate at an opposite side of the CID, be connected to a second middle plate that is connected to the first electrode by a lead tab, and be protruded to a terminal hole that is formed in the cap plate to be deformed in the first surface of the cap plate. The electrode terminal may be formed in a hollow structure. 
         [0020]    The fastening member may include a first bolt and a second bolt that penetrate through the first insulator and the first middle plate and that are fastened to the cap plate. 
         [0021]    The fastening member may include a first welding member and a second welding member that penetrate through the first insulator and the first middle plate and that are welded to the cap plate. 
         [0022]    At least one of the above and other features and advantages may also be realized by providing a rechargeable battery module, including unit cells of two or more square-shaped rechargeable batteries that are disposed to be stacked in one direction, and a bus bar that connects the unit cells. Each unit cell may include an electrode terminal that is housed in a case and that is electrically connected to a first electrode of an electrode group including the first electrode and a second electrode and that is electrically insulated from a cap plate covering the case to be protruded to a first surface of the cap plate, and a CID that electrically connects the second electrode and the cap plate and that interrupts an electrical connection when a voltage greater than a setting voltage is charged. The CID may include a membrane that is disposed at a second surface that is formed at an opposite side of the first surface of the cap plate to be electrically connected to the second electrode and that interrupts an electrical connection when a voltage greater than a setting voltage is charged, a first insulator that is disposed at the second surface of the cap plate and at least one surface of the membrane to support the membrane, and a fastening member that fastens the cap plate and the first insulator. The bus bar is welded to the electrode terminal of the unit cell of one side and to the cap plate adjacent to the membrane of the unit cell of the other side. 
         [0023]    The CID may include a first middle plate that is disposed at a surface of an opposite side of the cap plate of the first insulator, that is connected to the second electrode by a lead tab, and that includes a first penetration hole corresponding to the membrane, and a sub-plate that is connected at an opposite side of the first insulator of the first middle plate. The membrane may include a first flange that is connected to the second surface of the cap plate and a first welding part that is protruded to an opposite side of the cap plate in the first flange to be electrically connected to the first middle plate, and the sub-plate may include a second flange that is connected to the first middle plate and a second welding part that is protruded toward the first welding part in the second flange, wherein the second welding part may pass through the first penetration hole and be welded to the first welding part. 
         [0024]    The cap plate may have a second penetration hole corresponding to the first penetration hole. 
         [0025]    The membrane may include a fracture part that is inverted into the second penetration hole to function as a vent. 
         [0026]    The bus bar may be welded to cover the second penetration hole at the cap plate side. 
         [0027]    The bus bar may have a discharge hole that is formed to correspond to the second penetration hole. 
         [0028]    The fastening member may include a first rivet and a second rivet that fasten the cap plate, the first insulator, and the first middle plate, and the bus bar may connect the electrode terminal of the unit cell of one side and the cap plate corresponding to the membrane that is disposed between the first rivet and the second rivet of the unit cell of the other side with a diagonal structure. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0029]    The above and other features and advantages will become more apparent to those of ordinary skill in the art by describing in detail exemplary embodiments with reference to the attached drawings, in which: 
           [0030]      FIG. 1  illustrates a perspective view of a rechargeable battery according to an exemplary embodiment; 
           [0031]      FIG. 2  illustrates a cross-sectional view of the rechargeable battery of  FIG. 1 ; 
           [0032]      FIG. 3  illustrates an exploded perspective view of members that are fastened to a cap plate in the rechargeable battery of  FIG. 1 ; 
           [0033]      FIG. 4  illustrates a cross-sectional view of a CID according to another exemplary embodiment; 
           [0034]      FIG. 5  illustrates a cross-sectional view of a CID according to another exemplary embodiment; 
           [0035]      FIG. 6  illustrates a partial perspective view of a state of connecting a cap plate and an electrode terminal of unit cells of a rechargeable battery by a bus bar in a rechargeable battery module according to an exemplary embodiment; and 
           [0036]      FIG. 7  illustrates a top plan view of  FIG. 6 . 
       
    
    
     DESCRIPTION OF REFERENCE NUMERALS INDICATING PRIMARY ELEMENTS IN THE DRAWINGS 
       [0037]      
         [0000]    
       
         
               
               
             
               
             
               
               
             
               
             
               
               
             
               
             
               
               
             
               
             
               
               
             
           
               
                   
               
             
             
               
                 100: rechargeable battery 
                 200, 500, 600: current interrupt device 
               
               
                 10: electrode group 
                 11: positive electrode 
               
               
                 111, 121: uncoated part 
                 12: negative electrode 
               
               
                 13: separator 
                 20: case 
               
               
                 30: cap plate 
                 31: terminal hole 
               
             
          
           
               
                 32: electrolyte solution injection hole 
               
             
          
           
               
                 33: seal stopper 
                 41: electrode terminal 
               
               
                 51: membrane 
                 511, 541: first and second flanges 
               
             
          
           
               
                 512, 542: first and second welding parts 
               
             
          
           
               
                 513: fracture part 
                 52, 152: first insulator 
               
               
                 521: penetration hole 
               
             
          
           
               
                 831, 832: first and second welding members 
               
             
          
           
               
                 53, 73, 83: fastening member 
                 531, 532: first and second rivets 
               
               
                 522, 533: insulation member 
                 54: sub-plate 
               
             
          
           
               
                 55, 65: first and second middle plates 
               
               
                 551, 34: first and second penetration holes 
               
             
          
           
               
                 61, 62: lead tab 
                 731, 732: first and second volts 
               
               
                 70: bus bar 
                 71: discharge hole 
               
               
                 63: second insulator 
                 831, 832: first and second welding 
               
               
                   
                 members 
               
               
                   
               
             
          
         
       
     
       DETAILED DESCRIPTION 
       [0038]    Korean Patent Application No. 10-2009-0056161, filed on Jun. 23, 2009, in the Korean Intellectual Property Office, and entitled: “Rechargeable Battery and Module Thereof,” is incorporated by reference herein in its entirety. 
         [0039]    Example embodiments will now be described more fully hereinafter with reference to the accompanying drawings; however, they may be embodied in different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. 
         [0040]    In the drawing figures, the dimensions of layers and regions may be exaggerated for clarity of illustration. It will also be understood that when a layer or element is referred to as being “on” another layer or substrate, it can be directly on the other layer or substrate, or intervening layers may also be present. In addition, it will also be understood that when a layer is referred to as being “between” two layers, it can be the only layer between the two layers, or one or more intervening layers may also be present. Like reference numerals refer to like elements throughout. 
         [0041]      FIG. 1  illustrates a perspective view of a rechargeable battery according to a first exemplary embodiment, and  FIG. 2  illustrates a cross-sectional view of the rechargeable battery of  FIG. 1 . Referring to  FIGS. 1 and 2 , a rechargeable battery  100  may include a case  20 , e.g., prismoid-shaped, that houses an electrode group  10 , a cap plate  30  that closes and seals an opening that is formed at one side of the case  20 , an electrode terminal  41  that is protruded to the outside through a terminal hole  31  that is formed in the cap plate  30 , and lead tabs  61  and  62  that connect the cap plate  30  and the electrode terminal  41 , respectively, to the electrode group  10 . 
         [0042]    The electrode group  10  may include a first electrode  12 , e.g., a negative electrode  12 , and a second electrode  11 , e.g., a positive electrode  11 , respectively disposed at both surfaces of a separator  13 , which is an insulator. The positive electrode  11 , the negative electrode  12 , and the separator  13  may be spirally wound together in a jelly roll form. 
         [0043]    The positive electrode  11  and the negative electrode  12  may each be formed with a current collecting body of a thin plate metal foil, and may include a coated part and uncoated parts  111  and  121  that are differentiated according to whether they are coated with an active material. That is, the coated part is an area that is coated with an active material, and the uncoated parts  111  and  121  are areas that are not coated with an active material. 
         [0044]    The uncoated parts  111  and  121  may be respectively formed at each side end of a length direction of the positive electrode  11  and the negative electrode  12 , respectively, and may be disposed at opposite sides. The uncoated parts  111  and  121  may be connected to the lead tabs  61  and  62 , respectively, and the lead tabs  61  and  62  may be connected to the cap plate  30  and the electrode terminal  41 , respectively. 
         [0045]    In the first exemplary embodiment, because the uncoated part  111  of the positive electrode  11  is connected to the cap plate  30  through the lead tab  61 , the cap plate  30  may define a positive electrode terminal. Because the uncoated part  121  of the negative electrode  12  is connected to the electrode terminal  41  through the lead tab  62 , the electrode terminal  41  may define a negative electrode terminal. Alternatively, the cap plate  30  may define a negative electrode terminal, and the electrode terminal  41  may define a positive electrode terminal (not shown). 
         [0046]    The case  20  may form an entire external appearance of the rechargeable battery  100  and may be formed of a conductive metal, e.g., one or more of aluminum, aluminum alloy, nickel-plated steel, etc. The case  20  may define a housing space for the electrode group  10 , e.g., in a rectangular shape of a hexahedron, i.e., a cuboid. If the case  20  is a prismoid, the case  20  may have a wide heat radiating area and, thus, may have a better heat radiating performance, e.g., as compared to that of a cylindrical case. 
         [0047]    The cap plate  30  may be formed with a thin plate and may be coupled to an opening that is formed at one side of the case  20  to close and seal the opening. The cap plate  30  may include an electrolyte solution injection hole  32  through which an electrolyte solution may be injected into the sealed case  20 . After the electrolyte solution is injected, the electrolyte solution injection hole  32  may be sealed by a seal stopper  33 . Further, in order to prevent explosion of the rechargeable battery  100  due to an increase of internal pressure thereof, when the internal pressure of the rechargeable battery  100  reaches a setting value, a vent part (not shown), e.g., included in the cap plate  30 , may rupture to discharge internal gas. 
         [0048]    In order to secure safety for overcharge, the rechargeable battery  100  according to the first exemplary embodiment may include a current interrupt device (CID)  200 . The CID  200  may be between the electrode group  10  and the cap plate  30 . For example, as illustrated in  FIG. 2 , the CID  200  may be between the positive electrode  11  and the cap plate  30 . In another example, the CID  200  may be provided between the negative electrode  12  and the electrode terminal  41  (not shown). The CID  200  will be described in more detail below with reference to  FIG. 3 . 
         [0049]      FIG. 3  illustrates an exploded perspective view of members that are fastened to the cap plate  30  in the rechargeable battery  100 . Referring to  FIGS. 2 and 3 , the CID  200  may include a membrane  51 , a first insulator  52 , and a fastening member  53 . 
         [0050]    As illustrated in  FIG. 3 , the membrane  51  of the CID  200  may include a first flange  511  and a first welding part  512  attached to the first flange  511 . The first flange  511  may be attached, e.g., welded, to a lower surface  30   a  of the cap plate  30 , so the first flange  511  and the lower surface  30   a  of the cap plate  30  may be in a surface contact state. For example, the first flange  511  may be welded to the cap plate  30  by a laser. The first welding part  512  may be convexly formed on the first flange  511 , e.g., extend downward from the first flange  511 , and may be disposed at the lower surface  30   a  of the cap plate  30 . The first welding part  512  may be electrically connected to the positive electrode  11 , so current flows through the first welding part  512  to sustain a general operating state of the rechargeable battery  100 . Therefore, when the electrical connection between the first welding part  512  and the positive electrode  11  breaks, e.g., upon overcharging, current through the first welding part  512  is interrupted to stop overcharging of the rechargeable battery  100 . 
         [0051]    The first insulator  52  of the CID  200  may be parallel to a bottom of the case  20 , and may be disposed at the lower surface  30   a  of the cap plate  30  and at a lower surface of the first flange  511 . For example, as illustrated in  FIG. 2 , a first portion of the first insulator  52  may be on, e.g., directly on, the lower surface  30   a  of the cap plate  30 , and a second portion of the first insulator  52  may be on, e.g., directly on, a lower surface of the first flange  511 . In other words, as illustrated in  FIGS. 2-3 , the first flange  511  may be between the cap plate  30  and the second portion of the first insulator  52 . As further illustrated in  FIG. 2 , the lower surface  30   a  of the cap plate  30  and the lower surface of the first flange  511  may be formed at the same plane, i.e., may be substantially level, so the first insulator  52  may support the first flange  511  of the membrane  51  by a substantially uniform surface pressure. In other words, the first flange  511  may be securely supported between, e.g., directly between, the cap plate  30  and the first insulator  52  that overlaps the substantially flat surface defined by the lower surfaces of the cap plate  30  and first flange  511 . 
         [0052]    The fastening member  53  of the CID  200  may be formed as a pair to fasten the cap plate  30  and the first insulator  52  at both sides of the membrane  51 . In other words, as illustrated in  FIG. 2 , the membrane  51  may be between two fastening members  53 . Therefore, the membrane  51  may sustain a strong bonding state with the cap plate  30  by the cap plate  30  and the first insulator  52  that receive a fastening force of the fastening member  53 . 
         [0053]    Further, as illustrated in  FIGS. 2 and 3 , the CID  200  may include a sub-plate  54  and a first middle plate  55 . For example, the sub-plate  54  may include a second flange  541  that is electrically connected to the positive electrode  11 , and a second welding part  542  that is convexly formed upward from the second flange  541 . The first middle plate  55  may be disposed at a lower surface of the first insulator  52 , i.e., the first insulator  52  may be between the cap plate  30  and the first middle plate  55 , and may be electrically connected to the positive electrode  11  by the lead tab  61 . Further, as illustrated in  FIGS. 2-3 , the first middle plate  55  may include a first penetration hole  551  at a portion corresponding to the membrane  51 . When the CID  200  is operated, i.e., when pressure increases in the battery case  20 , the first penetration hole  551  may apply internal pressure to the membrane  51 . 
         [0054]    When the first middle plate  55  is provided, the second flange  541  of the sub-plate  54  may be welded to a lower surface of the first middle plate  55 , i.e., the first middle plate  55  may be between the second flange  541  and the cap plate  30 . For example, the second flange  541  may be welded to the first middle plate  55  by ultrasonic waves. The second welding part  542  of the sub-plate  54  may pass through the first penetration hole  551 , and may be connected, e.g., welded, to the first welding part  512  of the membrane  51  during the general operating state of the rechargeable battery  100 . Therefore, as illustrated in  FIG. 2 , the positive electrode  11  of the electrode group  10  may be electrically connected to the cap plate  30  via the lead tab  61 , the first middle plate  55 , the sub-plate  54 , and the membrane  51 . 
         [0055]    As illustrated in  FIG. 2 , when the first insulator  52  is integrally formed, i.e., as a single uniform member, to overlap the first middle plate  55 , the first insulator  52  may have a penetration hole  521  therethrough corresponding to the first penetration hole  551  of the first middle plate  55 , thereby allowing the membrane  51  and the sub-plate  54  to be connected. In another example, the first insulator  52  may be independently provided at both sides of a connection part of the membrane  51  and the sub-plate  54 , i.e., as two separate portions defining the penetration hole  521 , (not shown). 
         [0056]    According to exemplary embodiments, since the sub-plate  54  is attached, e.g., welded, in a surface contact state to the first middle plate  55  by the second flange  541 , a structure in which the first middle plate  55  supports the sub-plate  54  may be formed. Further, an electrical connection structure of the sub-plate  54  and the first middle plate  55  may be stabilized, and a welding structure of the sub-plate  54  and the membrane  51  may be stably sustained. Accordingly, electrical resistance between the first middle plate  55 , the sub-plate  54 , and the membrane  51  may be reduced. 
         [0057]    The fastening member  53  of the CID  200  may be formed in various structures, and may include first and second rivets  531  and  532 , as illustrated in  FIGS. 2 and 3 . The first and second rivets  531  and  532  may fasten the cap plate  30 , the first insulator  52 , and the first middle plate  55  at both sides of the membrane  51 . Therefore, the membrane  51  may sustain a strong bonding state with the cap plate  30  by the cap plate  30  and the first insulator  52  that receive a fastening force of the fastening member  53 . In this case, as illustrated in  FIG. 2 , the first and second rivets  531  and  532  may be installed by interposing an insulation member  533  that penetrates through the first middle plate  55 , the first insulator  52 , and the cap plate  30 . The insulation member  533  may be integrally formed with the first insulator  52  (not shown) or may be separated from the first insulator  52  ( FIG. 3 ). By a strong fastening force of the first middle plate  55  and the first insulator  52 , the membrane  51  and the sub-plate  54  that are welded to the first middle plate  55  may stably sustain a welding structure. Thereby, electrical resistance may be reduced between the sub-plate  54  and the membrane  51 . 
         [0058]    The cap plate  30  may have a second penetration hole  34  at a position corresponding to, e.g., overlapping, the first penetration hole  551  and the membrane  51 . When the first welding part  512  of the membrane  51  is separated from the second welding part  542  of the sub-plate  54  due to overcharge, the second penetration hole  34  may facilitate an upward air flow, i.e., relative to the lower surface  30   a  of the cap plate  30  (two-point chain line in  FIG. 2 ), at an upper surface of the membrane  51 . Therefore, a rising separation operation of the membrane  51  may be undisturbed. When the sub-plate  54  is fractured, an electrical connection between the sub-plate  54  and the cap plate  30  is interrupted. 
         [0059]    Further, as illustrated in  FIGS. 2 and 3 , the membrane  51  may include a fracture part  513 . In detail, although the rechargeable battery  100  may have a separate vent part (not shown), the rechargeable battery  100  may include a vent part in the CID  200 , e.g., the rechargeable battery  100  may include only the vent part in the CID  200  without the separate vent part. 
         [0060]    That is, the vent part may be formed in the membrane  51 , i.e., the fracture part  513 . In more detail, referring again to  FIGS. 2 and 3 , when the membrane  51  is applied with internal pressure due to a fracture of the sub-plate  54 , the membrane  51  may rupture via the fracture part  513  while being inverted into the second penetration hole  34  (one-point chain line of  FIG. 2 ). Thus, gas may be discharged out of the rechargeable battery  100  to the outside, thereby preventing explosion of the rechargeable battery  100  due to an increase of internal pressure. 
         [0061]    Referring back to  FIG. 2 , the electrode terminal  41  may have a structure that is protruded to the outside through the terminal hole  31 , and may be formed at an opposite side of the cap plate  30  with respect to the CID  200 . A second insulator  63  may be interposed on the lower surface  30   a  of the cap plate  30 , and may extend in the terminal hole  31  between the cap plate  30  and the electrode terminal  41  to electrically insulate the electrode terminal  41  from the cap plate  30 . A second middle plate  65  may be disposed on the lower surface  30   a  of the cap plate  30 , i.e., the second insulator  63  may be between the second middle plate  65  and the lower surface  30   a  of the cap plate  30 , and may be connected to the negative electrode  12  by the lead tab  62 . 
         [0062]    As illustrated in  FIG. 2 , the electrode terminal  41  may be integral with the second middle plate  65 . The electrode terminal  41  may extend from the second middle plate  65 , may protrude through the terminal hole  31 , and may deform at a periphery of the terminal hole  31  of an upper surface  30   b  of the cap plate  30 . For example, the electrode terminal  41  may be formed with a rivet structure. Further, the electrode terminal  41  may be formed in a hollow structure to be easily deformed in the upper surface  30   b  of the cap plate  30 . 
         [0063]      FIG. 4  illustrates a cross-sectional view of a CID  500  according to a second exemplary embodiment. Referring to  FIG. 4 , the CID  500  may have a substantially same structure as the CID  200  discussed previously with reference to  FIGS. 2 and 3 , with the exception of having first and second bolts  731  and  732  as a fastening member  73 , instead of the first and second rivets  531  and  532  of the fastening member  53 . 
         [0064]    In detail, as illustrated in  FIG. 4 , the first and second bolts  731  and  732  may penetrate through the first middle plate  55  and a first insulator  152 , and may be coupled to the cap plate  30  by screw threads. In this case, the first insulator  152  may form an electrical insulation structure between the first middle plate  55  and each of the first and second bolts  731  and  732 . The first insulator  152  may further include an insulation member  522  that is interposed between head portions of the first and second bolts  731  and  732  and a lower surface of the first middle plate  55 . 
         [0065]      FIG. 5  illustrates a cross-sectional view of a CID  600  according to a third exemplary embodiment. Referring to  FIG. 5 , the CID  600  may have a substantially same structure as the CID  200  discussed previously with reference to  FIGS. 2 and 3 , with the exception of having first and second welding members  831  and  832  as a fastening member  83 , instead of the first and second rivets  531  and  532  of the fastening member  53 . 
         [0066]    In detail, as illustrated in  FIG. 5 , the first and second welding members  831  and  832  may penetrate through the first middle plate  55  and the first insulator  152 , and may be welded (W) to the cap plate  30 . In this case, the first insulator  152  may form an electrical insulation structure between the first and second welding members  831  and  832  and the first middle plate  55 . The first insulator  152  may further include the insulation member  522  that is interposed between head portions of the first and second fastening members  831  and  832  and the lower surface of the first middle plate  55 . 
         [0067]      FIG. 6  illustrates a partial perspective view of a state of connecting the cap plate  30  and the electrode terminal  41  of unit cells by a bus bar in a rechargeable battery module according to an exemplary embodiment, and  FIG. 7  illustrates a top plan view of  FIG. 6 . Referring to  FIGS. 6 and 7 , a rechargeable battery module  400  may include a plurality of unit cells according to exemplary embodiments, e.g., a plurality of square-shaped rechargeable batteries  100 . For example, the rechargeable battery module  400  may be formed by disposing two or more stacked rechargeable batteries  100 , i.e., unit cells, in one direction, and connecting the rechargeable batteries  100  of a unit cell in series by a bus bar  70 . 
         [0068]    For example, as illustrated in  FIG. 6 , a first side  70   a  of the bus bar  70  may be welded to the electrode terminal  41  of one rechargeable battery  100  that forms a unit cell and a second side  70   b  of the bus bar  70  may be welded to the cap plate  30  of another rechargeable battery  100  that forms a unit cell, thereby electrically connecting the electrode terminal  41  and the cap plate  30  of two adjacent rechargeable batteries  100  in series. For example, the bus bar  70  may be made of a low resistance material, e.g., Al and Cu, and may be used when using resistance welding, friction welding, or laser welding. 
         [0069]    In order to maximally use an internal space of the case  20 , the electrode terminal  41  that is connected to the negative electrode  12  may be formed at one side end of the cap plate  30 , and the CID  200  that is connected to the positive electrode  11  may be formed at another side of the cap plate  30 . Because of the first rivet  531 , even though the CID  200  is disposed at a side end of the cap plate  30 , a distance between the CID  200  and a center of the cap plate  30  may be smaller than a distance between the electrode terminal  41  and the center of the cap plate  30 . 
         [0070]    Further, when the bus bars  70  are connected in series, it is necessary to form a minimal current path between the electrode terminal  41  of the negative electrode  12  and the cap plate  30  of the positive electrode  11 . For this purpose, the bus bar  70  may connect the electrode terminal  41  and the CID  200 . The CID  200  may be disposed between the first and second rivets  531  and  532 . Therefore, the bus bar  70  may be disposed in a diagonal structure between two rechargeable batteries  100  to connect the two rechargeable batteries  100  in series. 
         [0071]    The bus bar  70  may be welded in a structure such that it covers a second penetration hole  34  of the cap plate  30  and has a discharge hole  71  that is formed to correspond to the second penetration hole  34  of the cap plate  30 . When the membrane  51  of the CID  200  also functions as a vent, the discharge hole  71  may allow internal gas to be discharged upon fracturing of the membrane  51 . That is, when the discharge holes  71  are connected in series, a shortest current path may be embodied, and the membrane  51  may function as a vent. 
         [0072]    The cap plate  30  that is connected to the positive electrode  11  of the electrode group  10  to form a positive electrode terminal may be planar, and the electrode terminal  41  that is connected to the negative electrode  12  to form a negative electrode terminal may protrude through the cap plate  30 . Therefore, in the rechargeable battery module  400 , a stable serial connection structure may be formed and sustained. 
         [0073]    According to an exemplary embodiment, a rechargeable battery may include CID between an electrode of the electrode group and a cap plate in order to secure safety for overcharge. The CID may include a membrane is welded between the cap plate and another plate, i.e., a first middle plate or a sub-plate that is connected to an electrode of the electrode group, thereby reducing electrical resistance. Further, the membrane in the CID may be disposed and supported between the cap plate and a first insulator that is fastened by a fastening member, thereby improving durability during vibration or impact. 
         [0074]    Exemplary embodiments have been disclosed herein, and although specific terms are employed, they are used and are to be interpreted in a generic and descriptive sense only and not for purpose of limitation. Accordingly, it will be understood by those of ordinary skill in the art that various changes in form and details may be made without departing from the spirit and scope of the present invention as set forth in the following claims.