Abstract:
There is a provided a secondary battery capable of preventing unloading and rotating caused by possible vibration or shock by increasing a coupling force among the vent plate, the insulator, and the cap-down that compose the cap assembly of the secondary battery. To increase the coupling force among the vent plate, the insulator, and the cap-down, protrusions and corresponding grooves or holes, and grooves with step areas may be formed. Alternatively, a plurality of insulators may be formed in a divided form. A secondary battery with a reliable cap assembly can be implemented through such a structural change.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application claims the benefit of Korean Patent Application No. 2007-86143 filed Aug. 27, 2007, the disclosure of which is hereby incorporated herein by reference in its entirety. 
       BACKGROUND OF THE INVENTION 
       [0002]    1. Technical Field 
         [0003]    The present invention relates to a secondary battery, and more particularly, to a secondary battery having high durability against vibration and shock and has improved coupling of a cap assembly. 
         [0004]    2. Discussion of Related Art 
         [0005]    Typical batteries are classified into primary batteries and secondary batteries. The primary batteries are often disposable because they either cannot be charged or can only be charged very slowly. On the other hand, the secondary batteries exhibit reversible conversion between chemical energy and electrical energy, thus allowing for repetitive charging and discharging. 
         [0006]    Secondary batteries may be classified into nickel batteries and lithium batteries depending on the active material of their electrode. In particular, an amount of energy that can be charged depends on materials of the electrodes and electrolyte. The lithium secondary batteries are capable of storing the most energy in the same volume and are widely used as power supplies for modern cell phones, notebook computers, camcorders, personal digital assistants (PDAs), etc. 
         [0007]    The lithium secondary batteries use lithium oxide as a cathode active material and carbon oxide as an anode active material. The lithium secondary batteries may be classified into lithium ion batteries using liquid electrolyte and lithium polymer batteries using polymer electrolyte depending on electrolyte types. The lithium secondary batteries may be of several types, including a cylindrical type, a polygonal type, a pouch type, and the like. 
         [0008]    Such a secondary battery generally comprises an electrode assembly having a cathode plate and an anode plate wound with a separator interposed therebetween, a case for accommodating the electrode assembly, and a cap assembly located on an opening of the case for sealing the case, with a gasket interposed between the cap assembly and the case. 
         [0009]    Specifically, the cap assembly often comprises a top cap member or cap-up, a vent plate, an insulator, and a bottom cap member or cap-down. 
         [0010]    The insulator is often vertically fastened with the vent plate. In this case, first fastening members of the insulator are coupled with insertion portions of the vent plate, causing the first fastening members to interfere with bent portions of the vent plate. 
         [0011]    Since the interference with the bent portions increases with an increasing size of the first fastening member, the first fastening member is not allowed to increase above a predetermined size. 
         [0012]    As a result, a coupling force between the first fastening members and the insertion portions to couple the insulator with the vent plate is limited and the insulator is more likely to rotate and be unloaded or otherwise dislodged due to possible vibration or shock. 
         [0013]    The insulator and the cap-down are also coupled to each other by second fastening members of the insulator. In this case, the second fastening members vertically presses the cap-down to be fixed thereto. This may cause the cap-down to rotate due to possible vibration or shock. 
         [0014]    The rotation of the cap-down may break a weld between the vent and the cap-down. Thus, a current path from the electrode assembly to the cap-up can be abnormally blocked impeding the normal operation of the battery. 
       SUMMARY OF THE INVENTION 
       [0015]    An aspect of the present invention provides a secondary battery having an increased coupling force among a vent plate, an insulator and a cap-down. 
         [0016]    Exemplary embodiments of the present invention provide a secondary battery comprising: an electrode assembly formed with a separator interposed between a cathode plate and an anode plate; a case for accommodating the electrode assembly; and a cap assembly for sealing the case, wherein the cap assembly comprises a vent plate, an insulator including a plurality of protrusions, and a cap-down including a plurality of grooves or holes located corresponding to the protrusions. 
         [0017]    Other embodiments of the present invention provide a secondary battery comprising: an electrode assembly formed with a separator interposed between a cathode plate and an anode plate; a case for accommodating the electrode assembly; and a cap assembly for sealing the case, wherein the cap assembly comprises a vent plate including a plurality of step areas, an insulator, and a cap-down. 
         [0018]    Other embodiments of the present invention provide a secondary battery comprising: an electrode assembly formed with a separator interposed between a cathode plate and an anode plate; a case for accommodating the electrode assembly; and a cap assembly for sealing the case, wherein the cap assembly comprises a vent plate including a plurality of protrusions, an insulator including a plurality of grooves or holes located corresponding to the protrusions, and a cap-down. 
         [0019]    Other embodiments of the present invention provide a secondary battery comprising: an electrode assembly formed with a separator interposed between a cathode plate and an anode plate; a case for accommodating the electrode assembly; and a cap assembly for sealing the case, wherein the cap assembly comprises a vent plate, an insulator, and a cap-down including a plurality of step areas. 
         [0020]    Other embodiments of the present invention provide a secondary battery comprising: an electrode assembly formed with a separator interposed between a cathode plate and an anode plate; a case for accommodating the electrode assembly; and a cap assembly for sealing the case, wherein the cap assembly comprises a vent plate, a plurality of insulators each including a plurality of protrusions, and a cap-down including a plurality of grooves or holes located corresponding to the protrusions. 
         [0021]    Thus, in the secondary battery of the present invention, the cap-down, the insulator and the vent plate are prevented from rotating and being unloaded due to possible vibration or shock, thereby improving coupling force and durability of the cap assembly. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0022]    The above and other features and advantages of the present invention will become more apparent to those of ordinary skill in the art by describing in detail preferred embodiments thereof with reference to the attached drawings in which: 
           [0023]      FIG. 1A  is a cross-sectional view illustrating a secondary battery according to a first embodiment of the present invention; 
           [0024]      FIG. 1B  is an assembly view illustrating a cap assembly of the secondary battery according to the first embodiment of the present invention; 
           [0025]      FIG. 2A  is an assembly view illustrating a cap assembly of the secondary battery according to a second embodiment of the present invention; 
           [0026]      FIG. 2B  is a cross-sectional view illustrating a secondary battery according to a second embodiment of the present invention; 
           [0027]      FIG. 3  is an assembly view illustrating a cap assembly of the secondary battery according to a third embodiment of the present invention; 
           [0028]      FIG. 4  is an assembly view illustrating a cap assembly of the secondary battery according to a fourth embodiment of the present invention; 
           [0029]      FIG. 5  is an assembly view illustrating a cap assembly of the secondary battery according to a fifth embodiment of the present invention; 
           [0030]      FIG. 6  is an assembly view illustrating a cap assembly of the secondary battery according to a sixth embodiment of the present invention; 
           [0031]      FIG. 7  is an assembly view illustrating a cap assembly of the secondary battery according to a seventh embodiment of the present invention; 
           [0032]      FIG. 8  is an assembly view illustrating a cap assembly of the secondary battery according to an eighth embodiment of the present invention; 
           [0033]      FIG. 9A  is a cross-sectional view illustrating a cap assembly of the secondary battery according to a ninth embodiment of the present invention; 
           [0034]      FIG. 9B  is an assembly view illustrating a cap assembly of the secondary battery according to the ninth embodiment of the present invention; 
           [0035]      FIG. 10A  is a cross-sectional view illustrating a cap assembly of the secondary battery according to a tenth embodiment of the present invention; 
           [0036]      FIG. 10B  is an assembly view illustrating a cap assembly of the secondary battery according to the tenth embodiment of the present invention; 
           [0037]      FIG. 11  is an enlarged cross-sectional view illustrating a step area of a vent plate according to the present invention; and 
           [0038]      FIG. 12  is an enlarged cross-sectional view illustrating a step area of a cap-down according to the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0039]    The present invention will now be described more fully hereinafter with reference to the accompanying drawings, in which preferred embodiments of the invention are shown. This invention may, however, be embodied in different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided as teaching examples of the invention. In the drawings, a length, a thickness and the like of layers and areas may be exaggerated for the convenience of explanation. Like numbers refer to like elements. 
       The First Embodiment 
       [0040]      FIG. 1A  is a cross-sectional view illustrating a secondary battery according to a first embodiment of the present invention. 
         [0041]      FIG. 1B  is an assembly view illustrating a cap assembly of the secondary battery according to the first embodiment of the present invention. 
         [0042]    Referring to  FIGS. 1A and 1B , a secondary battery according includes an electrode assembly  110  having a cathode plate  111  and an anode plate  112  wound with a separator  113  interposed therebetween. The assembly  110  includes a cathode current collecting plate  115  and an anode current collecting plate (not shown) electrically connected to the electrode assembly  110  for collecting current generated from the cathode plate  111  and the anode plate  112 , respectively. The battery also includes a case  120  for accommodating the electrode assembly  110 , and a cap assembly  200  coupled with the case  120  for sealing the case  120  and providing electrical connections to the electrode assembly  110 . 
         [0043]    The electrode assembly  110  includes the cathode plate  111  and the anode plate  112  coated with an active material with the separator  113  interposed therebetween. There are also non-coated portions  111   a  and  112   a  of the cathode and anode plates  111  and  112 , respectively, which are not coated with the active material. 
         [0044]    The cathode current collecting plate  115  and the anode current collecting plate (not shown) are electrically connected to the non-coated portions  111   a  and  112   a  of the cathode and anode plates  111  and  112  which are wound to face each other. 
         [0045]    The cathode current collecting plate  115  is located between the cap assembly  200  and the electrode assembly  110  for electrically connecting the cathode plate  111  with the cap assembly  200 . The anode current collecting plate is located between the case  120  and the electrode assembly  110  for electrically connecting the anode plate  112  with the case  120 . 
         [0046]    The case  120  is formed of a conductive metal such as aluminum, an aluminum alloy, or nickel plated steel and has a cylindrical shape in which the electrode assembly  110  is placed. The case may be formed in various shapes other than the cylindrical shape. 
         [0047]    The cap assembly  200  includes a cap-up or upper cap member  160 , a vent plate  150 , an insulator  140  and a cap-down or lower cap member  130 . The cap assembly  200  is located at an opening of the case  120 , with an insulating gasket  170  interposed therebetween. 
         [0048]    When the secondary battery is overcharged above a charging condition or a gas is generated in the secondary battery due to a short circuit between the cathode plate  111  and the anode plate  112  of the electrode assembly  110 , internal pressure increases and the gas travels through a plurality of ventilation holes  131  of the cap-down  130  and lifts a vent  151  of the vent plate  150 . 
         [0049]    Accordingly, a weld A between the vent  151  and the cap-down  130  is broken, such that a current path from the electrode assembly  110  to the cap-up  160  via a lead  123  is blocked. 
         [0050]    If the internal pressure of the secondary battery further increases, the vent  151  is separated from the vent plate  150  to discharge the gas. Thus, the secondary battery is provided protection against explosion and fire. 
         [0051]    Connection of the vent plate  150 , the insulator  140  and the cap-down  130  of the cap assembly  200  will now be described in greater detail. 
         [0052]    First, the insulator  140  is vertically fastened with the vent plate  150 . In this case, a first fastening member  142  of the insulator  140  is coupled with an insertion portion  152  of the vent plate. 
         [0053]    Then, the insulator  140  and the cap-down  130  are coupled with each other by engagement between a plurality of protrusions  141  of the insulator  140  and a plurality of holes  132  of the cap-down  130 . 
         [0054]    The plurality of protrusions  141  correspond to, are inserted into, and are fixed to the plurality of holes  132  in the cap-down  130 . In one implementation, a laser may irradiate the protrusions  141  to firmly fix the insulator  140  to the cap-down  130 . The protrusions  141  of the insulator are melted by heat generated by the laser and solidified to be firmly coupled with the holes  132 . 
       The Second Embodiment 
       [0055]      FIG. 2A  is an assembly view illustrating a cap assembly of the secondary battery according to a second embodiment of the present invention. 
         [0056]      FIG. 2B  is a cross-sectional view illustrating a secondary battery according to a second embodiment of the present invention; 
         [0057]    A secondary battery according to the second embodiment of the present invention is the same in structure as the secondary battery according to the first embodiment except for the cap-down, the insulator, and the vent plate of the cap assembly. Accordingly, aspects of the present embodiment that are the same as in the first exemplary embodiment will not be described again. 
         [0058]    Referring to  FIGS. 2A and 2B , an insulator  140  is vertically coupled with the vent plate  150 . In this case, a first fastening member (not shown) of the insulator  140  is coupled with an insertion portion  152  of the vent plate. 
         [0059]    The vent plate  150  comprises a plurality of step areas  154  for increasing a coupling force between the vent plate  150  and the insulator  140 . 
         [0060]    The step areas  154  of the vent plate  150  may be apparent from an enlarged view of  FIG. 11 . Referring to  FIG. 11 , each step area  154  is formed at an edge of the vent plate  150  and has a groove  156 . 
         [0061]    Specifically, the step may be formed in a predetermined region around the groove  156  by applying a force to the vent plate  150  to form the groove  156 . 
         [0062]    The step areas  154  of the vent plate  150  can increase step-induced surface friction upon connection of the vent plate  150  with the insulator  140 , thus inhibiting rotation of the insulator  140 . 
         [0063]    The insulator  140  and the cap-down  130  having ventilation holes  131  are then coupled with each other by the second fastening members  143  of the insulator  140 . In this case, the cap-down  130  is vertically pressed by the second fastening members  143 . 
       The Third Embodiment 
       [0064]      FIG. 3  is an assembly view illustrating a cap assembly of the secondary battery according to a third embodiment of the present invention. 
         [0065]    A secondary battery according to the third embodiment of the present invention is the same in structure as the secondary battery according to the first embodiment except for the cap-down, the insulator, and the vent plate of the cap assembly. Accordingly, aspects of the present embodiment that are the same as in the first exemplary embodiment will not be described again. 
         [0066]    Referring to  FIG. 3 , first, an insulator  140  is vertically coupled with a vent plate  150 . In this case, a first fastening member (not shown) of the insulator  140  is coupled with an insertion portion  152  of the vent plate in a similar manner as discussed above in conjunction with  FIGS. 1A and 2B . 
         [0067]    The vent plate  150  comprises a plurality of step areas  154  for increasing a coupling force between the vent plate  150  and the insulator  140 . 
         [0068]    The step areas  154  of the vent plate  150  may be apparent from the enlarged view of  FIG. 11 . Referring to  FIG. 11 , each step area  154  is formed at an edge of the vent plate  150  and has a groove  156 . 
         [0069]    Specifically, the step may be formed in a predetermined region around the groove  156  by applying a force to the vent plate  150  to form the groove  156 . 
         [0070]    The step areas  154  of the vent plate  150  can increase step-induced surface friction upon connection of the vent plate  150  with the insulator  140 , thus preventing rotation of the insulator  140 . 
         [0071]    The insulator  140  and the cap-down  130  having ventilation holes  131  are coupled with each other by using a plurality of protrusions  141  of the insulator  140  and a plurality of holes  132  of the cap-down  130 . 
         [0072]    Thus, the plurality of protrusions  141  correspond to, are inserted into, and are fixed to the plurality of holes  132 . In this case, the protrusions  141  are irradiated with a laser so that the insulator  140  is firmly fixed to the cap-down  130 . 
         [0073]    The protrusions  141  are melted by heat generated by the irradiated laser and solidified to be firmly coupled with the holes  132 . 
       The Fourth Embodiment 
       [0074]      FIG. 4  is an assembly view illustrating a cap assembly of the secondary battery according to a fourth embodiment of the present invention. 
         [0075]    A secondary battery according to the fourth embodiment of the present invention is the same in structure as the secondary battery according to the first embodiment except for the cap-down, the insulator, and the vent plate of the cap assembly. Accordingly, aspects of the present embodiment that are the same as in the first exemplary embodiment will not be described again. 
         [0076]    Referring to  FIG. 4 , first, an insulator  140  is vertically coupled with a vent plate  150 . In this case, a first fastening members (not shown) of the insulator  140  is coupled with an insertion portion  152  of the vent plate in a manner similar to that discussed above in conjunction with  FIGS. 1A and 2B . 
         [0077]    The vent plate  150  and the insulator  140  are also coupled with each other by a plurality of protrusions  155  of the vent plate  150  and a plurality of holes  145  of the insulator  140 . 
         [0078]    Thus, the plurality of protrusions  155  correspond to, are inserted into, and are fixed to the plurality of holes  145 . In this case, the holes  145  are irradiated with a laser so that the vent plate  150  is firmly fixed to the insulator  140 . 
         [0079]    The holes  145  of the insulator  140  are melted by heat generated by the laser and solidified to be firmly coupled with the protrusions  155 . 
         [0080]    Also, the protrusions  155  may be coupled with the holes  145  by applying a physical force to the protrusions  155 . 
         [0081]    The insulator  140  and the cap-down  130  having ventilation holes  131  are then coupled with each other by using second fastening members  143  of the insulator  140 . In this case, the cap-down  130  is vertically pressed by the second fastening members  143 . 
       The Fifth Embodiment 
       [0082]      FIG. 5  is an assembly view illustrating a cap assembly of the secondary battery according to a fifth embodiment of the present invention. 
         [0083]    A secondary battery according to the fifth embodiment of the present invention is the same in structure as the secondary battery according to the first embodiment except for the cap-down, the insulator, and the vent plate of the cap assembly. Accordingly, aspects of the present embodiment that are the same as in the first exemplary embodiment will not be described again. 
         [0084]    Referring to  FIG. 5 , first, an insulator  140  is vertically coupled with a vent plate  150 . In this case, a first fastening member (not shown) of the insulator  140  is coupled with an insertion portion  152  of the vent plate in a manner similar to that discussed above in conjunction with  FIGS. 1A and 2B . 
         [0085]    The insulator  140  and the cap-down  130  having ventilation holes  131  are then coupled with each other by using second fastening members  143  of the insulator  140 . In this case, the cap-down  130  is vertically pressed by the second fastening members  143 . 
         [0086]    The cap-down  130  comprises a plurality of step areas  133  for increasing a coupling force between the insulator  140  and the cap-down  130 . 
         [0087]    The step areas  133  of the cap-down  130  may be apparent from an enlarged view of  FIG. 12 . Referring to  FIG. 12 , each step area  133  is formed at an edge of the cap-down  130  and has a groove  134 . 
         [0088]    Specifically, the step may be formed in a predetermined region around the groove  134  by applying a force to the cap-down  130  to form the groove  134 . 
         [0089]    The step area  133  of the cap-down  130  can increase step-induced surface friction upon connection of the cap-down  130  with the insulator  140 , thus preventing rotation of the cap-down  130 . 
       The Sixth Embodiment 
       [0090]      FIG. 6  is an assembly view illustrating a cap assembly of the secondary battery according to a sixth embodiment of the present invention. 
         [0091]    A secondary battery according to the sixth embodiment of the present invention is the same in structure as the secondary battery according to the first embodiment except for the cap-down, the insulator, and the vent plate of the cap assembly. Accordingly, aspects of the present embodiment that are the same as in the first exemplary embodiment will not be described again. 
         [0092]    Referring to  FIG. 6 , first, an insulator  140  is vertically coupled with a vent plate  150 . In this case, a first fastening member (not shown) of the insulator  140  is coupled with an insertion portion  152  of the vent plate in a manner similar to that discussed above in conjunction with  FIGS. 1A and 2B . 
         [0093]    The vent plate  150  comprises a plurality of step areas  154  for increasing a coupling force between the vent plate  150  and the insulator  140 . 
         [0094]    The step areas  154  of the vent plate  150  may be apparent from the enlarged view of  FIG. 11 . Referring to  FIG. 11 , each step area  154  is formed at an edge of the vent plate  150  and has a groove  156 . 
         [0095]    Specifically, the step may be formed in a predetermined region around the groove  156  by applying a force to the vent plate  150  to form the groove  156 . 
         [0096]    Accordingly, the step areas  154  of the vent plate  150  can increase step-induced surface friction upon connection of the vent plate  150  with the insulator  140 , thus preventing rotation of the insulator  140 . 
         [0097]    The insulator  140  and the cap-down  130  having ventilation holes  131  are then coupled with each other by second fastening members  143  of the insulator  140 . In this case, the cap-down  130  is vertically pressed by the second fastening members  143 . 
         [0098]    The cap-down  130  comprises a plurality of step areas  133  for increasing a coupling force between the insulator  140  and the cap-down  130 . 
         [0099]    The step areas  133  of the cap-down  130  may be apparent from the enlarged view of  FIG. 12 . Referring to  FIG. 12 , each step area  133  is formed at an edge of the cap-down  130  and has a groove  134 . 
         [0100]    Specifically, the step may be formed in a predetermined region around the groove  134  by applying a force to the cap-down  130  to form the groove  134 . 
         [0101]    The step areas  133  of the cap-down  130  can increase step-induced surface friction upon connection of the cap-down  130  with the insulator  140 , thus preventing rotation of the insulator  130 . 
       The Seventh Embodiment 
       [0102]      FIG. 7  is an assembly view illustrating a cap assembly of the secondary battery according to a seventh embodiment of the present invention. 
         [0103]    A secondary battery according to the seventh embodiment of the present invention is the same in structure as the secondary battery according to the first embodiment except for the cap-down, the insulator, and the vent plate of the cap assembly. Accordingly, aspects of the present embodiment that are the same as in the first exemplary embodiment will not be described again. 
         [0104]    Referring to  FIG. 7 , first, an insulator  140  is vertically coupled with a vent plate  150 . In this case, a first fastening member (not shown) of the insulator  140  is coupled with an insertion portion  152  of the vent plate in a manner similar to that discussed above in conjunction with  FIGS. 1A and 2B . 
         [0105]    The vent plate  150  and the insulator  140  are also coupled with each other by a plurality of protrusions  155  of the vent plate  150  and a plurality of holes  145  of the insulator  140 . 
         [0106]    Thus, the plurality of protrusions  155  correspond to, are inserted into, and are fixed to the plurality of holes  145 . In this case, the holes  145  are irradiated with a laser so that the vent plate  150  is firmly fixed to the insulator  140 . The holes  145  of the insulator  140  are melted by heat generated by the laser and solidified to be firmly coupled with the protrusions  155 . Also, the protrusions  155  may be coupled with the holes  145  by applying a physical force to the protrusions  155 . 
         [0107]    The insulator  140  and the cap-down  130  having ventilation holes  131  are then coupled with each other by second fastening members  143  of the insulator  140 . In this case, the cap-down  130  is vertically pressed by the second fastening members  143 . 
         [0108]    The cap-down  130  comprises a plurality of step areas  133  for increasing a coupling force between the insulator  140  and the cap-down  130 . 
         [0109]    The step areas  133  of the cap-down  130  may be apparent from an enlarged view of  FIG. 12 . Referring to  FIG. 12 , each step area  133  is formed at an edge of the cap-down  130  and has a groove  134 . 
         [0110]    Specifically, the step may be formed in a predetermined region around the groove  134  by applying a force to the cap-down  130  to form the groove  134 . 
         [0111]    The step area  133  of the cap-down  130  can increase step-induced surface friction upon connection of the cap-down  130  with the insulator  140 , thus preventing rotation of the cap-down  130 . 
       The Eighth Embodiment 
       [0112]      FIG. 8  is an assembly view illustrating a cap assembly of the secondary battery according to an eighth embodiment of the present invention. 
         [0113]    A secondary battery according to the eighth embodiment of the present invention is the same in structure as the secondary battery according to the first embodiment except for the cap-down, the insulator, and the vent plate of the cap assembly. Accordingly, aspects of the present embodiment that are the same as in the first exemplary embodiment will not be described again. 
         [0114]    Referring to  FIG. 8 , first, an insulator  140  is vertically coupled with a vent plate  150 . In this case, a first fastening member (not shown) of the insulator  140  is coupled with an insertion portion  152  of the vent plate in a manner similar to that discussed above in conjunction with  FIGS. 1A and 2B . 
         [0115]    The vent plate  150  and the insulator  140  are also coupled with each other by a plurality of protrusions  155  of the vent plate  150  and a plurality of holes  145  of the insulator  140 . 
         [0116]    Thus, the plurality of protrusions  155  correspond to, are inserted into, and are fixed to the plurality of holes  145 . In this case, the holes  145  are irradiated with a laser so that the vent plate  150  is firmly fixed to the insulator  140 .The holes  145  of the insulator  140  are melted by heat generated by the irradiated laser and solidified to be firmly coupled with the protrusions  155 .Also, the protrusions  155  may be coupled with the holes  145  by applying a physical force to the protrusions  155 . 
         [0117]    The insulator  140  and the cap-down  130  having ventilation holes  131  are then coupled with each other by a plurality of protrusion  141  of the insulator  140  and a plurality of holes  132  of the cap-down  130 . 
         [0118]    The plurality of protrusions  141  correspond to, are inserted into, and are fixed to the plurality of holes  132 . In this case, the laser may be irradiated to the protrusion  141  to firmly fix the insulator  140  to the cap-down  130 . 
         [0119]    The protrusions  141  of the insulator are melted by heat generated by the laser and solidified to be firmly coupled with the holes  132 . 
       The Ninth Embodiment 
       [0120]      FIG. 9A  is a cross-sectional view illustrating a cap assembly of the secondary battery according to a ninth embodiment of the present invention. 
         [0121]      FIG. 9B  is an assembly view illustrating a cap assembly of the secondary battery according to the ninth embodiment of the present invention. 
         [0122]    A secondary battery according to the ninth embodiment of the present invention is the same in structure as the secondary battery according to the first embodiment except for the cap-down, the insulator, and the vent plate of the cap assembly. Accordingly, aspects of the present embodiment that are the same as in the first exemplary embodiment will not be described again. 
         [0123]    Referring to  FIGS. 9A and 9B , an insulator is divided into two: a first insulator  140   a  and a second insulator  140   b.  The first insulator  140   a  and the second insulator  140   b  are horizontally inserted into and coupled with an insertion portion  152  of a vent plate. 
         [0124]    Horizontally fastening of the divided insulators  140   a  and  140   b  with the vent plate  150  can prevent interference between a bent portion  153  of the vent plate and first fastening members  142  of the divided insulators  140   a  and  140   b,  which has been conventionally caused by the undivided insulator vertically fastened with the vent plate  150 . 
         [0125]    Also, the first fastening member  142  of the plurality of divided insulators  140   a  and  140   b  is allowed to be formed larger than the first fastening member of the undivided insulator, thus increasing a coupling force between the vent plate  150  and the insulators  140   a  and  140   b.    
         [0126]    The insulators  140   a  and  140   b  and a cap-down  130  having ventilation holes  131  are then coupled with each other by a plurality of protrusions  141  of the insulators  140   a  and  140   b  and a plurality of holes  132  of the cap-down  130 . 
         [0127]    The plurality of protrusions  141  correspond to, are inserted into, and are fixed to the plurality of holes  132 . In this case, a laser may be irradiated to the protrusions  141  to firmly fix the insulators  140   a  and  140   b  to the cap-down  130 . The protrusions  141  of the insulator are melted by heat generated by the laser and solidified to be firmly coupled with the holes  132 . 
       The Tenth Embodiment 
       [0128]      FIG. 10A  is a cross-sectional view illustrating a cap assembly of the secondary battery according to a tenth embodiment of the present invention. 
         [0129]      FIG. 10B  is an assembly view illustrating a cap assembly of the secondary battery according to the tenth embodiment of the present invention. 
         [0130]    A secondary battery according to the tenth embodiment of the present invention is the same in structure as the secondary battery according to the first embodiment except for the cap-down, the insulator, and the vent plate of the cap assembly. Accordingly, aspects of the present embodiment that are the same as in the first exemplary embodiment will not be described again. 
         [0131]    Referring to  FIGS. 10A and 10B , an insulator is divided into two: a first insulator  140   a  and a second insulator  140   b.  The first insulator  140   a  and the second insulator  140   b  are horizontally inserted into and coupled with an insertion portion  152  of a vent plate. 
         [0132]    Horizontally fastening of the divided insulators  140   a  and  140   b  with the vent plate  150  can prevent interference between a bent portion  153  of the vent plate and first fastening members  142  of the divided insulators  140   a  and  140   b,  which has been conventionally caused by the undivided insulator vertically fastened with the vent plate  150 . 
         [0133]    Thus, the first fastening member  142  of the plurality of divided insulators  140   a  and  140   b  is allowed to be formed larger than the first fastening member of the undivided insulator, thus increasing a coupling force between the vent plate  150  and the insulators  140   a  and  140   b.    
         [0134]    The vent plate  150  comprises a plurality of step areas  154  for increasing a coupling force between the vent plate  150  and the insulators  140   a  and  140   b.    
         [0135]    The step areas  154  of the vent plate  150  may be apparent from the enlarged view of  FIG. 11 . Referring to  FIG. 11 , each step area  154  is formed at an edge of the vent plate  150  and has a groove  156 . 
         [0136]    Specifically, the step may be formed in a predetermined region around the groove  156  by applying a force to the vent plate  150  to form the groove  156 . 
         [0137]    The step area  154  of the vent plate  150  can increase step-induced surface friction upon connection of the vent plate  150  with the insulators  140   a  and  140   b,  thus preventing rotation of the insulators  140   a  and  140   b.    
         [0138]    The insulators  140   a  and  140   b  and a cap-down  130  having ventilation holes  131  are then coupled with each other by a plurality of protrusions  141  of the insulators  140   a  and  140   b  and a plurality of holes  132  of the cap-down  130 . 
         [0139]    The plurality of protrusions  141  correspond to, are inserted into, and are fixed to the plurality of holes  132 . In this case, the laser may irradiate the protrusion  141  to firmly fix the insulators  140   a  and  140   b  to the cap-down  130 . 
         [0140]    The protrusions  141  of the insulator are melted by heat generated by the laser and solidified to be firmly coupled with the holes  132 . 
         [0141]    Although the first insulator  140   a  and the second insulator  140   b  in a divided form have been described by way of example in the ninth and tenth embodiments, a plurality of insulators may be included. 
         [0142]    The first to tenth embodiments of the present invention have been described with respect to the plurality of holes  132  and  145  corresponding to and coupled with the plurality of protrusions  141  and  155  with reference to the drawings. However, the holes  132  and  145  are not limited thereto but may be any sort of indentation, such as holes, grooves, etc. without departing from the present teachings. 
         [0143]    The invention has been described using preferred exemplary embodiments. However, it is to be understood that the scope of the invention is not limited to the disclosed embodiments. On the contrary, the scope of the invention is intended to include various modifications and alternative arrangements within the capabilities of persons skilled in the art using presently known or future technologies and equivalents. The scope of the claims, therefore, should be accorded the broadest interpretation so as to encompass all such modifications and similar arrangements.