CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application claims the benefit of U.S. Provisional Application No. 61/480,195, filed on Apr. 28, 2011, in the United States Patent and Trademark Office, the disclosure of which is incorporated herein in its entirety by reference. 
     
    
     BACKGROUND 
       [0002]    1. Field 
         [0003]    Embodiments relate to a terminal of a secondary battery and a method of assembling the terminal. 
         [0004]    2. Description of the Related Art 
         [0005]    Secondary batteries are rechargeable unlike primary batteries. Among such secondary batteries, a low capacity battery including a battery cell in the form of a pack may be used for small portable electronic devices such as cellular phones and camcorders, and a high capacity battery including dozens of battery cells connected to one another may be used as a motor-driving power source for electric scooters, hybrid vehicles, or electric vehicles. 
         [0006]    Secondary batteries are manufactured in various shapes such as a cylindrical shape and a prismatic shape. A secondary battery is typically constructed as follows: an electrode assembly formed by inserting an insulating separator between positive and negative electrode plates is placed in a case together with electrolyte; and a cap plate is on the case. The electrode assembly is connected to positive and negative terminals which protrude from the cap plate and are exposed to the exterior of the secondary battery. 
       SUMMARY 
       [0007]    An aspect of the present invention provides a terminal of a secondary battery in which a collecting plate and a terminal plate are coupled using a coupling terminal to improve the electricity collecting efficiency and coupling force, and a method of assembling the terminal. 
         [0008]    A secondary battery includes an electrode assembly; a first terminal electrically connected to the electrode assembly, wherein the first terminal includes a first collecting plate contacting the electrode assembly and having at least one opening; a first terminal plate comprising at least one protrusion extending into the at least one opening; and a first coupling terminal extending through the first terminal plate and electrically coupled to the first collecting plate; a case housing the electrode assembly; and a cap assembly sealing the case. 
         [0009]    In one embodiment, the first terminal plate has a plurality of protrusions and the first collecting plate has a plurality of openings. Further, in one embodiment, the first collecting plate has a terminal opening through which the first coupling terminal protrudes. A first coupling ring may be located between the first collecting plate and the first coupling terminal. 
         [0010]    In one embodiment, the first terminal plate has a coupling opening configured to accommodate the first coupling terminal, and the coupling opening may be threaded. Further, in one embodiment, n the first terminal plate has a pressing section that is compressed against the first coupling terminal. 
         [0011]    In one embodiment, the secondary battery further includes a second terminal electrically connected to the electrode assembly, wherein the second terminal includes a second collecting plate contacting the electrode assembly and having at least one opening; a second terminal plate comprising at least one protrusion extending into the at least one opening of the second terminal plate; and a second coupling terminal extending through the second terminal plate and electrically coupled to the second collecting plate. 
         [0012]    In one embodiment, the first coupling terminal and the first terminal plate are made from different materials and in one embodiment, the first coupling terminal has a greater strength than the first terminal plate. 
         [0013]    Further, in one embodiment the cap assembly includes a cap plate, wherein the first terminal plate extends into the cap plate. 
         [0014]    According to the terminal of the secondary battery and the method of assembling the terminal, the collecting plate and the terminal plate are coupled using the coupling terminal so that the electricity collecting efficiency and coupling force of the secondary battery can be improved. 
         [0015]    According to the terminal of the secondary battery and the method of assembling the terminal, the collecting plate and the terminal plate are electrically connected through the coupling terminal so that a current passage can be shortened to reduce terminal electric resistance. 
         [0016]    According to the terminal of the secondary battery and the method of assembling the terminal, the terminal plate and the coupling terminal are coupled by a bolt-nut structure and pressed so that the coupling terminal may not be rotated when a bus bar or a nut is coupled to the coupling terminal. 
         [0017]    According to the terminal of the secondary battery and the method of assembling the terminal, since a current flows from the collecting plate to a bus bar through the terminal plate having a relatively large sectional area, the electric resistance of the terminal can be reduced owing to the wide current passage. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0018]      FIG. 1  is a perspective view illustrating a secondary battery according to an embodiment. 
           [0019]      FIG. 2  is a sectional view of the secondary battery taken along line I-I′ of  FIG. 1 . 
           [0020]      FIG. 3  is an enlarged sectional view illustrating portion A of  FIG. 2 . 
           [0021]      FIGS. 4A through 4C  are views illustrating a method of assembling a terminal of the secondary battery according to an embodiment. 
           [0022]      FIG. 5  is a view illustrating a method of coupling secondary batteries with bus bars according to an embodiment. 
           [0023]      FIG. 6  is a sectional view illustrating a coupled state of a terminal of a secondary battery and a bus bar according to an embodiment. 
       
    
    
     DETAILED DESCRIPTION 
       [0024]    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. Hereinafter, embodiments will be described in detail with reference to the accompanying drawings. 
         [0025]      FIG. 1  is a perspective view illustrating a secondary battery  100  according to an embodiment.  FIG. 2  is a sectional view of the secondary battery  100  taken along line I-I′ of  FIG. 1 .  FIG. 3  is an enlarged sectional view illustrating portion A of  FIG. 2 . 
         [0026]    Referring to  FIGS. 1 through 3 , the secondary battery  100  of the current embodiment includes an electrode assembly  110 , a first terminal  120 , a second terminal  130 , a case  140 , and a cap assembly  150 . 
         [0027]    The electrode assembly  110  is formed by winding or stacking a first electrode plate  111 , a separator  113 , and a second electrode plate  112  which have a thin plate or film shape. The first electrode plate  111  may function as a negative electrode, and the second electrode plate  112  may function as a positive electrode. Alternatively, the first electrode plate  111  and the second electrode plate  112  may function oppositely. 
         [0028]    The first electrode plate  111  is formed by applying a first electrode active material such as graphite or carbon to a first electrode collector formed of metal foil such as nickel or copper foil. The first electrode plate  111  includes a first electrode non-coating portion  111   a  to which the first electrode active metal is not applied. The first electrode non-coating portion  111   a  functions as a current flow passage between the first electrode plate  111  and the outside of the first electrode plate  111 . In the current embodiment, materials that can be used to form the first electrode plate  111  are not limited to the above-mentioned materials. 
         [0029]    The second electrode plate  112  is formed by applying a second electrode active material such as a transition metal oxide to a second electrode collector formed of metal foil such as aluminum foil. The second electrode plate  112  includes a second electrode non-coating portion  112   a  to which the second electrode active metal is not applied. The second electrode non-coating portion  112   a  functions as a passage for a current between the second electrode plate  112  and the outside of the second electrode plate  112 . In the current embodiment, materials that can be used to form the second electrode plate  112  are not limited to the above-mentioned materials. 
         [0030]    The polarities of the first and second electrode plates  111  and  112  may be reversed with respect to each other. 
         [0031]    The separator  113  may be located between the first electrode plate  111  and the second electrode plate  112  to prevent a short circuit and allow movement of lithium ions. The separator  113  may be formed of a polyethylene film, a polypropylene film, or a film including polyethylene and polypropylene. In the current embodiment, materials that can be used to form the separator  113  are not limited to the above-mentioned materials. 
         [0032]    The first and second terminals  120  and  130  are coupled to both end parts of the electrode assembly  110  in a manner such that the first and second terminals  120  and  130  are electrically connected to the first and second electrode plates  111  and  112 , respectively. 
         [0033]    Substantially, the electrode assembly  110  is accommodated in the case  140  together with electrolyte. The electrolyte may include an organic solvent such as ethylene carbonate (EC), propylene carbonate (PC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC); and a lithium salt such as LiPF 6  or LiBF 4 . The electrolyte may be liquid, solid, or gel. 
         [0034]    The first terminal  120  is usually formed of a metal or an equivalent thereof, and is electrically connected to the first electrode plate  111 . The first terminal  120  includes a first collecting plate  121 , a first terminal plate  122 , a first coupling terminal  123 , and a first coupling ring  124 . 
         [0035]    The first collecting plate  121  makes contact with the first electrode non-coating portion  111   a  protruding from an end of the electrode assembly  110 . Substantially, the first collecting plate  121  is welded to the first electrode non-coating portion  111   a . The first collecting plate  121  is coupled to a lower side of a cap plate  151  (described later). The first collecting plate  121  has an approximately reverse L-shape, and a terminal hole  121   a  is formed in the upper portion of the first collecting plate  121 . The first coupling terminal  123  is fitted and coupled to the terminal hole  121   a . Protrusion holes  121   b  are formed at both sides of the terminal hole  121   a . Protrusions  122   c  of the first terminal plate  122  are fitted and coupled to the protrusion holes  121   b . For example, the first collecting plate  121  is formed of copper or a copper alloy. However, the material of the first collecting plate  121  is not limited thereto. 
         [0036]    The first terminal plate  122  is inserted through the cap plate  151  and is located on one side (the exterior side or top side) of the cap plate  151 . The first terminal plate  122  is electrically connected to the first collecting plate  121 . The first terminal plate  122  includes a body  122   a  and a protrusion part  122   b , and a penetration hole extends through a center portion of the first terminal plate  122 . A bolt part  123   b  of the first coupling terminal  123  may be coupled to the penetration hole, which may include a screw thread  122   d . The body  122   a  is coupled to the topside of the cap plate  151  and has an approximately hexahedral shape. A pressing region  122   e  is formed on a center portion of the body  122   a  around the penetration hole. After the first coupling terminal  123  is coupled to the first terminal plate  122 , the pressing region  122   e  may be pressed to fix the first coupling terminal  123  to the first terminal plate  122  by compression. The protrusion part  122   b  protrudes downward from the body  122   a  and has an approximately hexahedral shape. The protrusion part  122   b  is inserted through the cap plate  151  and is electrically connected to the first collecting plate  121 . The protrusions  122   c  are formed on the protrusion part  122   b  at both sides of the penetration hole. The protrusions  122   c  are coupled to the protrusion holes  121   b  of the first collecting plate  121  so that the first terminal plate  122  and the first collecting plate  121  can be electrically connected to each other. The first terminal plate  122  is electrically insulated from the cap plate  151 . For example, the first terminal plate  122  may be formed of copper, copper alloy, or an equivalent thereof. However, the material of the first terminal plate  122  is not limited thereto. The first terminal plate  122  and the cap plate  151  are insulated from each other. 
         [0037]    The first coupling terminal  123  is inserted through the first terminal plate  122  and is coupled to the first collecting plate  121  at the bottom side of the cap plate  151 . The first coupling terminal  123  includes a head part  123   a  and the bolt part  123   b . The head part  123   a  is coupled to the terminal hole  121   a  of the first collecting plate  121 . The head part  123   a  is bigger than the terminal hole  121   a  so that the first coupling terminal  123  cannot be separated from the first collecting plate  121 . The bolt part  123   b  protrudes upward from the head part  123   a  and includes a screw thread  123   c . The bolt part  123   b  is coupled to the terminal hole  121   a  of the first collecting plate  121  and the penetration hole of the first terminal plate  122 . In detail, the screw thread  123   c  of the bolt part  123   b  is engaged with the screw thread  122   d  formed on the penetration hole. In other words, since the first coupling terminal  123  and the first terminal plate  122  are coupled to each other by a bolt-nut structure, the first coupling terminal  123  and the first terminal plate  122  can be firmly coupled to each other. Furthermore, the first coupling terminal  123  can be fixed to prevent rotation by pressing the pressing region  122   e  of the first terminal plate  122  against the screw thread  123   c  of the first coupling terminal  123 . In one embodiment, the coupling terminal  123  is formed of a material having a greater strength than a material of the first terminal plate  122 . The first coupling terminal  123  may be formed of stainless steel for tighter coupling with the first terminal plate  122 . 
         [0038]    The first coupling ring  124  is located between the first collecting plate  121  and the first coupling terminal  123  for tight contact with the first collecting plate  121  and the first coupling terminal  123 . The first coupling ring  124  is formed of a material such as rubber and prevents permeation of moisture into the secondary battery  100  and leakage of electrolyte from the inside of the secondary battery  100 . 
         [0039]    The second terminal  130  may be formed of a metal or an equivalent thereof. The second terminal  130  is electrically connected to the second electrode plate  112 . The second terminal  130  includes a second collecting plate  131 , a second terminal plate  132 , a second coupling terminal  133 , and a second ring  134 . The second terminal  130  may have substantially the same shape as the first terminal  120  and thus, a detailed description thereof will not be repeated. The second collecting plate  131  and the second terminal plate  132  may be formed of aluminum, an aluminum alloy, or an equivalent thereof. However, the current embodiment is not limited to such materials. 
         [0040]    In addition, the second terminal plate  132  may be electrically connected to the cap plate  151 . In this case, the case  140  and the cap plate  151  (that will be described below in detail) may have the same polarity (for example, positive polarity) as the second terminal  130 . 
         [0041]    As described above, according to the embodiment, the collecting plates  121  and  131  are coupled to the terminal plates  122  and  132  through the coupling terminals  123  and  133 . In other words, the collecting plates  121  and  131  that collect electricity from the electrode assembly  110  are coupled to the terminal plates  122  and  132  through the coupling terminals  123  and  133  that will be coupled to bus bars. Therefore, both the electricity collecting efficiency and coupling reliability of the secondary battery  100  can be improved. In addition, since the collecting plates  121  and  131  and the terminal plates  122  and  132  are electrically connected through the coupling terminals  123  and  133 , the secondary battery  100  can have a simple structure and a shorter current passage for lower terminal electric resistance. 
         [0042]    Furthermore, according to the embodiment, since the coupling terminals  123  and  133  and the terminal plates  122  and  132  are coupled by a bolt-nut structure, rotation of the coupling terminals  123  and  133  can be prevented. Therefore, the coupling between the coupling terminals  123  and  133  and the terminal plates  122  and  132  can be more firm. In addition, after coupling bus bars to the coupling terminals  123  and  133 , nuts can be tightened to the coupling terminals  123  and  133  for more secure coupling between the coupling terminals  123  and  133  and the bus bars. 
         [0043]    Furthermore, according to embodiment, since current passages from the collecting plates  121  and  131  to bus bars are formed through the terminal plates  122  and  132  having relatively large sectional areas, the electric resistances of the terminals  120  and  130  can be reduced. 
         [0044]    The case  140  is formed of a conductive metal such as aluminum, aluminum alloy, or steel plated with nickel. The case  140  has an approximately hexahedral shape with an opening so that the electrode assembly  110 , the first terminal  120 , and the second terminal  130  can be inserted and placed in the case  140 .  FIG. 2  illustrates a state where the case  140  and the cap assembly  150  are coupled to each other. As will be appreciated, the peripheral part of the cap assembly  150  substantially corresponds to the opening of the case  140 . The inner surface of the case  140  may be treated to be electrically insulated from the electrode assembly  110 , the first and second terminals  120  and  130 , and the cap assembly  150 . 
         [0045]    The cap assembly  150  is coupled to the case  140 . In detail, the cap assembly  150  includes the cap plate  151 , sealing gaskets  152 , a plug  153 , a safety vent  154 , and insulation members  155 . Alternatively, the sealing gaskets  152  and the insulation members  155  may be considered as elements of the first and second terminals  120  and  130 . 
         [0046]    The cap plate  151  closes the opening of the case  140 . The cap plate  151  may be formed of the same material as the case  140 . For example, the cap plate  151  may be coupled to the case  140  by laser welding. As described above, the cap plate  151  may have the same polarity as the second terminal  130 . In this case, the cap plate  151  and the case  140  may have the same polarity. 
         [0047]    The sealing gaskets  152  are located between the cap plate  151  and the first and second terminal plates  122  and  132 . In detail, the sealing gaskets  152  are located between the cap plate  151  and the bodies  122   a  and  132   a  of the first and second terminal plates  122  and  132  for sealing between the cap plate  151  and the first and second terminal plates  122  and  132 . The sealing gaskets  152  prevent permeation of moisture into the secondary battery  100  or leakage of electrolyte from the inside of the secondary battery  100 . Each of the sealing gaskets  152  includes a first seal gasket  152   a  and a second seal gasket  152   b . The first seal gasket  152   a  is located inside the second seal gasket  152   b  and is surrounded by the second seal gasket  152   b . Since each of the sealing gaskets  152  is two parts, tighter sealing can be provided between the cap plate  151  and the first terminal plate  122  and the second terminal plate  132 . 
         [0048]    The plug  153  closes an electrolyte injection hole  151   a  of the cap plate  151 . The safety vent  154  is located within a vent hole  151   b  of the cap plate  151 , and a notch  154   a  is formed in the safety vent  154  so that the safety vent  154  can be opened at a preset pressure. 
         [0049]    The insulation members  155  are located between the cap plate  151  and the first and second collecting plates  121  and  131  to prevent a short circuit. In other words, the insulation members  155  prevent a short circuit between the first collecting plate  121  and the cap plate  151  and a short circuit between the second collecting plate  131  and the cap plate  151 . The insulation members  155  are also located between the cap plate  151  and the protrusion parts  122   b  and  132   b  of the first and second terminal plates  122  and  132  so that a short circuit can be prevented between the cap plate  151  and the first and second terminal plates  122  and  132 . 
         [0050]      FIGS. 4A through 4C  are views for sequentially explaining a method of assembling the terminal of the secondary battery according to an embodiment. In the following described, first and second terminals have the same structure. Thus, an explanation will be given based on the first terminal. 
         [0051]    Referring to  FIG. 4A , the insulation member  155  and the first collecting plate  121  are coupled to each other at a position under the first collecting plate  121 . Next, the sealing gasket  152  and the first terminal plate  122  are coupled to each other at a position above the cap plate  151 . Thus, the first terminal plate  122  is electrically insulated from the cap plate  151  by the sealing gasket  152  and the insulation member  155 . The protrusions  122   c  formed on the first terminal plate  122  are coupled to the protrusion holes  121   b  of the first collecting plate  121 . 
         [0052]    Referring to  FIG. 4B , the first coupling terminal  123  is inserted through the cap plate  151  from the bottom side of the cap plate  151 . In detail, the first coupling terminal  123  is inserted through the terminal hole  121   a  formed in the first collecting plate  121  and the penetration hole formed in the first terminal plate  122 . The first coupling ring  124  is located between the first collecting plate  121  and the first coupling terminal  123  for tight contact with the first collecting plate  121  and the first coupling terminal  123 . In addition, the screw thread  123   c  formed on the first coupling terminal  123  is engaged with the screw thread  122   d  formed on the first terminal plate  122 . Therefore, since the first coupling terminal  123  and the first terminal plate  122  are coupled to each other by a bolt-nut structure, the first coupling terminal  123  and the first terminal plate  122  can be firmly coupled to each other. 
         [0053]    Referring to  FIG. 4C , the pressing region  122   e  of the first terminal plate  122  is pressed to the first coupling terminal  123 . Then, rotation of the first coupling terminal  123  is prevented, and thus the coupling between the first coupling terminal  123  and the first terminal plate  122  can be maintained more securely. 
         [0054]      FIG. 5  is a view for explaining a method of coupling secondary batteries with bus bars according to an embodiment. 
         [0055]    As illustrated in  FIG. 5 , a plurality of secondary batteries  100  may be connected in series and/or in parallel with each other by using conductive bus bars  210 . Penetration holes  210   a  are formed at both sides of the bus bars  210 , and first and second coupling terminals  123  and  133  of the secondary batteries  100  are coupled to the penetration holes  210   a . Nuts  211  are coupled to the first and second coupling terminals  123  and  133  by applying large torque to the nuts  211 . 
         [0056]    Therefore, since the bus bars  210  are coupled to the first and second coupling terminals  123  and  133  by using the nuts  211 , the bus bars  210  can be in tight contact with first and second terminal plates  122  and  132 . 
         [0057]    Accordingly, since the bus bars  210  are securely coupled to the first and second coupling terminals  123  and  133  by using the nuts  211 , the coupling between the bus bars  210  and the first and second coupling terminals  123  and  133  can be more secure. In addition, since relatively large current passages are formed by the first and second terminal plates  122  and  132  and the bus bars  210 , terminal resistance can be reduced. 
         [0058]      FIG. 6  is a sectional view illustrating a coupled state of a terminal of a secondary battery and a bus bar according to an embodiment. 
         [0059]    Referring to  FIG. 6 , a bus bar  210  is coupled to a coupling terminal  123 . In detail, a bolt part  123   b  of the coupling terminal  123  is coupled to a penetration hole  210   a  of the bus bar  210 . A nut  211  is coupled to a portion of the bolt part  123   b  above the bus bar  210  so that the bus bar  210  can be brought into tight contact with a terminal plate  122 . Since the bus bar  210  is coupled to the terminal plate  122  having a relatively large sectional area, a wide current passage can be formed to reduce electric contact resistance. Furthermore, since the bus bar  210  is directly brought into contact with the terminal plate  122 , a current passage can be shortened to reduce electric resistance. 
         [0060]    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 disclosure as set forth in the following claims. 
         [0000]    
       
         
               
             
               
               
               
             
           
               
                   
               
               
                 REFERENCE NUMERAL 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                   
                 100: secondary battery 
                 110: electrode assembly 
               
               
                   
                 120: first terminal 
                 121: first collecting plate 
               
               
                   
                 122: first terminal plate 
                 123: first coupling terminal 
               
               
                   
                 124: first coupling ring 
                 130: second terminal 
               
               
                   
                 131: second collecting plate 
                 132: second terminal plate 
               
               
                   
                 133: second coupling terminal 
                 134: second coupling ring 
               
               
                   
                 140: case 
                 150: cap assembly 
               
               
                   
                 151: cap plate 
                 152: seal gasket 
               
               
                   
                 153: plug 
                 154: safety vent 
               
               
                   
                 155: insulation member
A secondary battery includes an electrode assembly; a first terminal electrically connected to the electrode assembly, wherein the first terminal includes a first collecting plate contacting the electrode assembly and having at least one opening; a first terminal plate comprising at least one protrusion extending into the at least one opening; and a first coupling terminal extending through the first terminal plate and electrically coupled to the first collecting plate; a case housing the electrode assembly; and a cap assembly sealing the case.