Abstract:
A secondary battery in which the structure of an insulating case arranged between an electrode assembly and a cap assembly prevents electrode tabs from being bent. The secondary battery includes: an electrode assembly including a positive electrode, a negative electrode, a separator interposed between the positive electrode and the negative electrode, and electrode tabs respectively extending from the positive electrode and the negative electrode; a can for accommodating the electrode assembly; a cap assembly attached to an opening of the can and connected to the electrode tabs; and an insulating case arranged between the electrode assembly and the cap assembly and including a hole through which one of the electrode tabs pass, the insulating case including barrier ribs respectively extending from at least portions of side walls of the hole.

Description:
CLAIM OF PRIORITY 
       [0001]    This application makes reference to, incorporates the same herein, and claims all benefits accruing under 35 U.S.C.§119 from an application earlier filed in the Korean Intellectual Property Office on 28 Mar. 2006 and there duly assigned Serial No. 10-2006-0027959. 
       BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The present invention relates to a secondary battery, and more particularly, to a secondary battery in which the structure of an insulating case inserted between an electrode assembly and a cap assembly prevents electrode tabs from being bent. 
         [0004]    2. Description of the Prior Art 
         [0005]    Secondary batteries have been recently researched and developed since secondary batteries can be recharged, are small, and have a high capacity. Representative secondary batteries that have been recently developed and used are nickel-Metal hydride (Ni-MH) batteries, lithium (Li) batteries, and lithium ion (Li-ion) batteries. 
         [0006]    In these secondary batteries, an electrode assembly composed of a positive electrode, a negative electrode, and a separator is accommodated in a can commonly formed of aluminum or an aluminum alloy; the can is completed by a cap assembly; an electrolyte is injected into the can, and the can is sealed. The can can be formed of steel. However, when the can is formed of aluminum or an aluminum alloy, the battery can be made light since the aluminum is light and is not corroded when the battery is used at a high voltage for a long time. 
         [0007]    The electrode terminals of the sealed secondary battery cells are electrically connected to the terminals of safety apparatus, such as a Positive Temperature Coefficient (PTC) device, a thermal fuse, or a Protective Circuit Module (PCM). The safety apparatus are connected to the positive electrode and the negative electrode to interrupt the current when the voltage of the battery rapidly increases due to excessive charge and discharge and to thus prevent the battery from being damaged. 
         [0008]    The safety apparatus and the bare cells are accommodated in an additional package where the safety apparatus and the bare cells are electrically connected to each other or where spaces between the safety apparatus and the bare cells are filled with a melted resin and the package is coated to form a battery pack. 
         [0009]      FIG. 1  is an exploded perspective view of a conventional secondary battery. Referring to  FIG. 1 , the conventional secondary battery includes a can  211 , an electrode assembly  212  accommodated within the can  211 , and a cap assembly mechanically attached to the opened top of the can  211  to seal the top of the can  211 . 
         [0010]    The electrode assembly  212  is formed by winding a thin plate or layer shaped positive electrode  213 , a separator  214 , and a negative electrode  215 . In the positive electrode  213 , a positive electrode tab  216  is electrically connected to the region of a positive electrode collector in which a positive electrode active material layer is not formed. In the negative electrode  215 , a negative electrode tab  217  is electrically connected to the region of a negative electrode collector in which a negative electrode active material layer is not formed. 
         [0011]    The positive electrode  213  and the negative electrode  215  and the positive and negative electrode tabs  216  and  217  can be arranged in reversed polarities. An insulating tape  218  can be wound on the boundaries where the positive and negative electrode tabs  216  and  217  are withdrawn from the electrode assembly  212  in order to prevent the positive and negative electrode tabs  216  and  217  and the positive and negative electrodes  213  and  215  from being shorted. 
         [0012]    The conventional can  211  is formed of a rectangular parallelepiped aluminum or aluminum alloy. The electrode assembly  212  is accommodated through the opened top of the can  211  so that the can  211  functions as the container of the electrode assembly  212  and the electrolyte. The can  211  can also function as a terminal. 
         [0013]    A planar plate shaped cap plate  110  having the size and shape corresponding to the opened top of the can  211  is provided in the cap assembly. A terminal through hole is formed in the center of the cap plate  110  so that an electrode terminal  130  can pass through. A tube shaped gasket  120  is provided outside the electrode terminal  130  that penetrates the center of the cap plate  110  so that the electrode terminal  130  and the cap plate  110  are electrically insulated from each other. An insulating plate  140  is provided under the cap plate  110  in the center of the cap plate  110  and around the terminal through hole. A terminal plate  150  is provided under the insulating plate  140 . An electrode injecting hole  112  is formed on one side of the cap plate  110 . A cap (not shown) is provided in the electrolyte injection hole  112  in order to seal the electrolyte injection hole  112  after the electrolyte has been injected. 
         [0014]    On the other hand, an insulating case  190  is further provided between the cap assembly and the electrode assembly  212 , and more particularly, under the cap assembly and on the electrode assembly  212 . A negative electrode tab hole  191  is formed on one side of the insulating case  190  so that the negative electrode tab  217  can pass through from the electrode assembly  212 . A positive electrode tab hole  192  is formed at the edge on the other side in the position corresponding to the positive electrode tab  216 . An electrolyte through hole  193  may or may not be additionally formed. 
         [0015]    The positive electrode tab  216  can be welded to the rear surface of the cap plate  110  through the positive electrode tab hole  192  of the insulating case  190  and the negative electrode tab  217  can be welded to the rear surface of the electrode terminal  130  through the negative electrode tab hole  191  so that the positive electrode tab  216  and the negative electrode tab  217  are withdrawn from the positive and negative electrodes  213  and  215  of the electrode assembly  212  to be connected to the cap plate  110  and the electrode terminal  130 . 
         [0016]      FIG. 2  is a side sectional view taken along the line A-A of  FIG. 1  of the insulating case and the electrode assembly that are attached to each other. As illustrated in  FIG. 2 , the insulating case  190  is provided between the cap assembly and the electrode assembly  212  that are illustrated in  FIG. 1  to electrically insulate the cap assembly and the electrode assembly  212  from each other. The insulating case  190  is formed of an insulating polymer resin and is preferably formed of polypropylene. 
         [0017]    On the other hand, since the negative electrode tab  217  withdrawn from the electrode assembly  212  to pass through the negative electrode tab hole  191  is connected to the electrode terminal  130  illustrated in  FIG. 1  in a short distance, the negative electrode tab  217  is folded in zigzags between the insulating case  190  and the cap assembly. 
         [0018]    When an external mechanical shock, such as falling or vibration, is applied to the secondary battery having the negative electrode tab folded in zigzags between the cap assembly and the insulating case as described above, the negative electrode tab folded in zigzags can be pushed downward and pressed by the insulating case. In this case, the pressed negative electrode tab is connected to the electrode assembly under the insulating case through the negative electrode tab hole having a predetermined gap so that the positive and negative electrodes can be shorted. Therefore, the stability of the secondary battery deteriorates. 
       SUMMARY OF THE INVENTION 
       [0019]    Accordingly, the present invention has been made to solve the above-mentioned problems occurring in the prior art, and an object of the present invention is to provide a secondary battery in which the structure of an insulating case inserted between an electrode assembly and a cap assembly prevent electrode tabs from being bent. 
         [0020]    In order to accomplish the object of the present invention, a secondary battery is provided including: an electrode assembly including a positive electrode, a negative electrode, a separator interposed between the positive electrode and the negative electrode, and electrode tabs respectively extending from the positive electrode and the negative electrode; a can for accommodating the electrode assembly; a cap assembly attached to an opening of the can and connected to the electrode tabs; and an insulating case arranged between the electrode assembly and the cap assembly and including a hole through which one of the electrode tabs passes, the insulating case including barrier ribs respectively extending from at least portions of side walls of the hole. 
         [0021]    At least portions of side walls of the hole are preferably an internal side wall of the hole running parallel to a lengthwise direction of the insulating case. 
         [0022]    The electrode tab that passes through the hole is preferably folded in zigzags between the cap assembly and the insulating case and electrically connects an electrode terminal of the cap assembly to one electrode of the electrode assembly. 
         [0023]    The barrier ribs are preferably inclined upward away from the insulating case. The barrier ribs preferably run parallel to a front surface of the insulating case. The barrier ribs preferably include tapered ribs whose thickness is reduced toward a center of the hole from the respective hole side wall. 
         [0024]    The starting points of the tapered ribs positioned in ends extending from the respective hole side wall are preferably thicker than the barrier ribs. 
         [0025]    The barrier ribs are preferably of a thickness in a range of 0.1 to 0.2 mm. The barrier ribs are integral with the insulating case and are of the same material. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0026]    A more complete appreciation of the present invention and many of the attendant advantages thereof, will be readily apparent as the present invention becomes better understood by reference to the following detailed description when considered in conjunction with the accompanying drawings in which like reference symbols indicate the same or similar components, wherein: 
           [0027]      FIG. 1  is an exploded perspective view of a conventional secondary battery; 
           [0028]      FIG. 2  is a side sectional view taken along the line A-A of an insulating case and an electrode assembly that are attached to each other; 
           [0029]      FIG. 3  is an exploded perspective view of a secondary battery according to an embodiment of the present invention; 
           [0030]      FIG. 4  is a perspective view of an enlarged ‘P’ part in the secondary battery of  FIG. 3 ; 
           [0031]      FIG. 5  is a side sectional view of barrier ribs taken along the line C-C of the insulating case of  FIG. 4 ; 
           [0032]      FIG. 6  is a side sectional view taken along the line B-B of  FIG. 3  of the insulating case and the electrode assembly that are attached to each other; 
           [0033]      FIG. 7  is a side sectional view of barrier ribs of an insulating case according to another embodiment of the present invention; and 
           [0034]      FIG. 8  is a side sectional view of barrier ribs of an insulating case according to still another embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0035]    Hereinafter, a secondary battery according to exemplary embodiments of the present invention are described in detail with reference to the accompanying drawings. 
         [0036]      FIG. 3  is an exploded perspective view schematically illustrating a secondary battery according to an embodiment of the present invention. Referring to  FIG. 3 , the secondary battery according to an embodiment of the present invention includes a can  411 , an electrode assembly  412  accommodated within the can  411 , and a cap assembly coupled with the opened top of the can  411  to seal up the top of the can  411 . 
         [0037]    The can  411  can be formed of a rectangular parallelepiped metal and can function as a terminal. According to the present invention, the can  411  functions as a positive terminal. Also, the can  411  can function as a negative terminal according to another embodiment. The electrode assembly  412  is accommodated through the opened top of the can  411 . 
         [0038]    A positive electrode  413  includes a positive electrode collector formed of a thin metal plate having excellent conductivity, for example, an aluminum foil and a positive electrode active material layer whose main component is a lithium based oxide, coating both surfaces of the foil. A positive electrode tab  416  is electrically connected to the region of the positive electrode collector in which the positive electrode active material layer is not formed on the positive electrode  413 . 
         [0039]    A negative electrode  415  includes a negative electrode collector formed of a thin metal plate having excellent conductivity, for example, a copper foil and a negative electrode active material layer whose main component is carbon, coating both surfaces of the foil. A negative electrode tab  417  is electrically connected to the region of the negative electrode collector in which the negative electrode active material layer is not formed on the negative electrode  415 . 
         [0040]    The positive electrode  413  and the negative electrode  415  and the positive and negative electrode tabs  416  and  417  can be arranged in reversed polarities. An insulating tape  418  can be wound on the boundaries where the positive and negative electrode tabs  416  and  417  are withdrawn from the electrode assembly  412  in order to prevent the positive and negative electrode tabs  416  and  417  and the positive and negative electrodes  413  and  415  from being shorted. 
         [0041]    A separator  414  is formed of polyethylene, polypropylene, or a co-polymer of the polyethylene and the polypropylene. The separator  414  is preferably formed to be wider than the positive and negative electrodes  413  and  415  in order to prevent the electrode plates from being shorted. 
         [0042]    A planar plate shaped cap plate  310  having the size and shape corresponding to the size and shape of the opened top of the can  411  is provided in the cap assembly. A terminal through hole is formed in the center of the cap plate  310  so that an electrode terminal  330  can pass through. A tube shaped gasket  320  is provided outside the electrode terminal  330  that penetrates the center of the cap plate  310  so that the electrode terminal  330  and the cap plate  310  are electrically insulated from each other. An insulating plate  340  is provided under the cap plate  310  in the center of the cap plate  310  and around the terminal through hole. A terminal plate  350  is provided under the insulating plate  340 . The cap plate  310  is attached to the can  411  by welding the cap plate  310  to the can  411  to function as the positive terminal like the can  411 . 
         [0043]    The electrode terminal  330  is inserted through the terminal through hole so that the gasket  320  wraps the outer circumference thereof. The bottom surface of the electrode terminal  330  is electrically connected to the terminal plate  350  where the insulating plate  340  is interposed. The electrode terminal  330  is a negative terminal whose polarity is reverse to the polarity of the cap plate  310 . 
         [0044]    The positive electrode tab  416  withdrawn from the positive electrode  413  is welded to the rear surface of the cap plate  310 . The negative electrode tab  417  withdrawn from the negative electrode  415  is welded to the lower end of the electrode terminal  330  and the negative electrode tab  417  is folded in zigzags. 
         [0045]    On the other hand, an insulating case  390  is provided on the front surface of the electrode assembly  412  in order to electrically insulate the electrode assembly  412  and the cap assembly from each other and to cover the upper end of the electrode assembly  412  at the same time. The insulating case  390  is formed of an insulating polymer resin and is preferably formed of polypropylene. A negative electrode tab hole  391  is formed on one side of the insulating case  390  so that the negative electrode tab  417  can pass through from the electrode assembly  412 . A positive electrode tab hole  392  is formed at the edge on the other side, that is, in the position corresponding to the positive electrode tab  416 . An electrolyte through hole  393  may or may not be additionally formed. 
         [0046]    An electrolyte injection hole  312  is formed on one side of the cap plate  310 . A cap (not shown) for sealing the electrolyte injection hole  312  after an electrolyte has been injected is provided in the electrolyte injection hole  312 . The cap is formed by placing a ball shaped mother material commonly formed of aluminum or a metal containing aluminum on the electrolyte injection hole to mechanically press fitting the mother material into the electrolyte injection hole. Therefore, the ball must have a diameter larger than the diameter of the electrolyte injection hole  312 . 
         [0047]    The cap assembly and the electrode assembly accommodated within the can  411  that have the above-described structures are insulated from each other by the insulating case  390 . 
         [0048]    The structure of the negative electrode tab hole  391  of the insulating case  390  is described below in detail with reference to  FIGS. 4 and 5 . 
         [0049]      FIG. 4  is a perspective view of an enlarged ‘P’ part in the secondary battery of  FIG. 3 .  FIG. 5  is a side sectional view of barrier ribs taken along the line C-C of the insulating case of FIG.  4 .  FIG. 6  is a side sectional view taken along the line B-B of  FIG. 3  of the insulating case and the electrode assembly that are attached to each other. 
         [0050]    As illustrated in  FIGS. 4 and 5 , the insulating case  390  of the secondary battery according to an embodiment of the present invention further includes barrier ribs  393  extended from both side walls of the negative electrode tab hole  391 . The both side walls of the negative electrode tab hole  391  from which the barrier ribs  393  are extended are side walls in a hole that runs parallel to the lengthwise direction of the insulating case. 
         [0051]    The barrier ribs  393  have a predetermined slope upward from the insulating case  390 . This is for easily inserting the negative electrode tab  417  into the insulating case  390  from the front surface of the insulating case  390  from which the negative electrode tab  417  is withdrawn. 
         [0052]    Since the barrier ribs  393  are extended from the both side walls of the negative electrode tab hole  391 , the space between the barrier ribs  393  is small so that the negative electrode tab  417  cannot easily pass through the barrier ribs  393  of the negative electrode tab hole  391 . Therefore, the barrier ribs  393  are formed to a thickness of 0.1 to 0.2 mm, which is smaller than the thickness of the insulating case  390  so that the negative electrode tab  417  can be easily withdrawn upward from the insulating case  390 . This is because, in the case where a force is applied to the barrier ribs  393  when the negative electrode tab  417  is inserted into the thin barrier ribs  393 , the barrier ribs  393  are pushed upward so that a space through which the negative electrode tab  417  can pass through can be secured. Therefore, the negative electrode tab  417  can easily pass through the barrier ribs  393  of the negative electrode tab hole  391 . The barrier ribs  393  can be formed to be integrated with the insulating case  390  of the insulating polymer resin, for example, the polypropylene like the insulating case  390 . 
         [0053]    As illustrated in  FIG. 6 , the barrier ribs  393  having the slope hold and fix the negative electrode tab  417  that passes through the lower part of the negative electrode tab hole  391  and the barrier ribs  393  and that is provided in zigzags on the insulating case  390 . Therefore, when an external force is applied to the secondary battery including the insulating case  390  having the barrier ribs  393 , the barrier ribs  393  prevent the negative electrode tab  417  formed in zigzags on the insulating case  390  from being pushed toward the lower part of the insulating case  390 . Also, when the negative electrode tab  417  formed in zigzags in a predetermined part is pushed toward the electrode assembly  412  to some extent, the barrier ribs  393  prevent the negative electrode tab  417  and the front surface of the electrode assembly  412  from being directly connected to each other. Therefore, the negative electrode tab  417  is not connected to the electrode assembly  412  positioned under the insulating case  390  so that it is possible to prevent the positive and negative electrodes from being shorted. 
         [0054]      FIG. 7  is a side sectional view of barrier ribs of an insulating case according to another embodiment of the present invention. 
         [0055]    The barrier ribs  593  of an insulating case  590  according to another embodiment of the present invention is different from the barrier ribs  393  of the insulating case  390  of  FIG. 5  in that the barrier ribs  593  do not have a slope and function the same as the barrier ribs  393  of the insulating case  390 . 
         [0056]    As illustrated in  FIG. 7 , the barrier ribs  593  of the insulating case  590  according to another embodiment of the present invention run parallel to the front surface of the insulating case  590  and are extended from the both side walls of a negative electrode tab hole  591 . The thickness of the barrier ribs  593  is 0.1 to 0.2 mm, which is small, like the thickness of the barrier ribs  393  of the insulating case  390  of  FIG. 5 . Therefore, when a force is applied to the barrier ribs  393  when the negative electrode tab  417  illustrated in  FIG. 3  is inserted into the barrier ribs  593 , the barrier ribs  593  are pushed upward so that a space through which the negative electrode tab  417  can pass can be secured. As a result, the negative electrode tab  417  can easily pass through the barrier ribs  593  of the negative electrode tab hole  591 . The barrier ribs  593  hold and fix the negative electrode tab  417  while the negative electrode tab  417  remaining pushed upward after passing through the small space between the barrier ribs  593 . The barrier ribs  593  can be formed to be integrated with the insulating case  590  of the insulating polymer resin, for example, the polypropylene like the insulating case  590 . 
         [0057]      FIG. 8  is a side sectional view of barrier ribs of an insulating case according to still another embodiment of the present invention. 
         [0058]    The barrier ribs  693  of an insulating case  690  according to still another embodiment of the present invention function the same as the barrier ribs  593  of the insulating case  590  of  FIG. 7 . However, the shape of the barrier ribs  693  is different from the shape of the barrier ribs  593 . 
         [0059]    As illustrated in  FIG. 8 , the barrier ribs  693  of the insulating case  690  according to still another embodiment of the present invention are extended from the both side walls of a negative electrode tab hole  691  and include tapered parts  693   a  whose thickness is reduced toward the center of the negative electrode tab hole  691  in the extended ends thereof. 
         [0060]    In the barrier ribs  693 , the parts excluding the tapered parts  693   a  are formed to a thickness of 0.1 to 0.2 mm, which is smaller than the thickness of the thickness of the insulating case  690  so that, when a force is applied to the barrier ribs  393  when the negative electrode tab  417  of  FIG. 3  is inserted into the barrier ribs  693 , the barrier ribs  693  are pushed upward so that the negative electrode tab  417  can easily pass through the space between the barrier ribs  693 . The barrier ribs  693  hold and fix the negative electrode tab  417  while the negative electrode tab  417  remaining pushed upward after passing through the small space between the barrier ribs  693 . 
         [0061]    The tapered parts  693   a  are reduced from the ends extended from the both side walls of the negative electrode tab hole  691  toward the center of the negative electrode tab hole  691  so that the internal surfaces thereof have a slope in the same direction as the barrier ribs  393  of  FIG. 5 . The internal surfaces of the tapered parts  693   a  having such a slope hold and fix the negative electrode tab  417  of  FIG. 3  that passes through the negative electrode tab hole  691  and the barrier ribs  693  and that is provided in zigzags on the insulating case  390 . The starting parts of the tapered parts positioned in the ends extended from the side wall of the negative electrode tab hole  691  can be formed to be thicker than the barrier ribs  693 . Therefore, parts of the tapered parts  693   a  that hold the negative electrode tab  410  are thicker than the other parts of the barrier ribs  693  to firmly hold the negative electrode tab  417 . 
         [0062]    The barrier ribs  693  can be formed to be integrated with the insulating case  690  of the same insulating polymer resin, for example, the polypropylene like the insulating case  690 . 
         [0063]    As described above, in the secondary battery according to an embodiment of the present invention, the barrier ribs extended from the internal wall of the electrode tab hole of the insulating case inserted between the electrode assembly and the cap assembly are formed to fix the electrode tab that passes through the electrode tab hole so that it is possible to prevent the electrode tab folded in zigzags on the insulating case from being bent downward from the insulating case by an external force. Also, when the electrode tab formed in zigzags in a predetermined part is pushed toward the electrode assembly to some extend, the barrier ribs prevent the electrode tab and the front surface of the electrode assembly from being directly connected to each other. Therefore, the electrode tab is not connected to the electrode assembly positioned under the insulating case so that it is possible to prevent the positive and negative electrodes from being shorted. Therefore, it is possible to secure the stability of the secondary battery. 
         [0064]    Although exemplary embodiments of the present invention have been described for illustrative purposes, those skilled in the art will appreciate that various modifications, additions and substitutions are possible, without departing from the scope and spirit of the present invention as defined by the accompanying claims.