Abstract:
A rechargeable battery adapted to prevent or reduce overcharge. A rechargeable battery includes a case containing an electrode assembly; a cap plate coupled to the case and sealing an opening of the case; a first electrode terminal connected to a first electrode of the electrode assembly and electrically connected to the case; a second electrode terminal connected to a second electrode of the electrode assembly and electrically insulated from the case when a pressure inside the case is less than a threshold pressure; and a short-circuit unit including a short-circuit member connected to the second electrode terminal, the short-circuit unit adapted to short-circuit the second electrode terminal to the case by swelling a portion of the case to contact the short-circuit member when the pressure inside the case is equal to or greater than the threshold pressure.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application claims priority to and the benefit of Korean Patent Application No. 10-2009-0018604 filed in the Korean Intellectual Property Office on Mar. 4, 2009, the entire content of which is incorporated herein by reference. 
       BACKGROUND 
       [0002]    1. Field 
         [0003]    Embodiments of the present invention relate to a rechargeable battery and a module thereof, and more particularly, to a rechargeable battery and a module thereof that can prevent or reduce overcharge. 
         [0004]    2. Description of the Related Art 
         [0005]    A large-capacity rechargeable battery may be used as a power supply for driving a motor of an electric vehicle or a hybrid electric vehicle (HEV). A large-capacity rechargeable battery is typically provided with a plurality of rechargeable batteries consisting of unit cells and is formed by connecting the unit cells to each other in series. 
         [0006]    A large-capacity rechargeable battery may have a circular or a prismatic shape. The prismatic shape generally provides a better heat radiating performance than the circular shape. Therefore, the prismatic shape is more advantageous than the circular shape with respect to the aspect of safety against overcharge. As a result, circular rechargeable batteries are typically provided with a current interrupt device (CID) for interrupting current in overcharge, while prismatic rechargeable batteries are typically not provided with a CID. 
         [0007]    However, recently, because the rechargeable battery adopted in the HEV, the plug-in hybrid electric vehicle (PHEV), and the electric vehicle is required to have high capacity, the size of the rechargeable battery may increase. In the case of the prismatic shape, a difference in heat radiation may be caused inside and outside of the unit cell due to an increase of a thickness thereof, such that safe charging may be difficult to provide. 
         [0008]    The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art. 
       SUMMARY 
       [0009]    Embodiments of the present invention provide a rechargeable battery and a module thereof for preventing or reducing overcharge. 
         [0010]    Embodiments of the present invention provide a rechargeable battery and a module thereof for providing stability from overcharge in a prismatic rechargeable battery having increased thickness. 
         [0011]    A rechargeable battery according to one exemplary embodiment of the present invention includes a case containing an electrode assembly; a cap plate coupled to the case and sealing an opening of the case; a first electrode terminal connected to a first electrode of the electrode assembly and electrically connected to the case; a second electrode terminal connected to a second electrode of the electrode assembly and electrically insulated from the case when a pressure inside the case is less than a threshold pressure; and a short-circuit unit including a short-circuit member connected to the second electrode terminal, the short-circuit unit adapted to short-circuit the second electrode terminal to the case by swelling a portion of the case to contact the short-circuit member when the pressure inside the case is equal to or greater than the threshold pressure. The case may have a prismatic hexahedron shape and the short-circuit unit may be on a surface of the case. 
         [0012]    The case may include a first surface and a second surface facing each other and each having a substantially same first area; a third surface and a fourth surface facing each other and being between the first and second surfaces, each of the third and fourth surfaces having a substantially same second area smaller than the first area; and a fifth surface facing the opening and having a width substantially equal to a width of the third and fourth surfaces. The short-circuit unit may be on the third surface or the fourth surface. The rechargeable battery may further include an insulating layer on outer surfaces of the case other than the surface having the short-circuit unit thereon. 
         [0013]    The first surface or the second surface may extend in a first direction and include cell barriers spaced from each other in a second direction that crosses the first direction, the cell barriers defining at least one flow passage therebetween for passage of a heat transfer medium therethrough. The rechargeable battery may further include an insulating layer on outer surfaces of the cell barriers. 
         [0014]    The short-circuit unit may include a swelling induction unit including the portion of the case, the portion of the case having a thickness that is less than a thickness of another portion of the case surrounding the portion, and the short-circuit member may face and be contactable with an outer surface of the portion of the case. 
         [0015]    The swelling induction unit may be concave on an inner surface of the portion of the case, and the short-circuit member may include a mounting portion mounted to the second electrode terminal, and a short-circuit end facing and contactable with the swelling induction unit. The short-circuit member may be bent between the mounting portion and the short-circuit end, the mounting portion being substantially horizontal, and the short-circuit end being substantially vertical. 
         [0016]    The short-circuit unit may further include a bracket connected to the case and supporting the short-circuit end, and an insulating member between the short-circuit end and the bracket. 
         [0017]    The first electrode terminal may be a positive electrode terminal, and the second electrode terminal may be a negative electrode terminal. 
         [0018]    The rechargeable battery may include an outer insulator on at least an outer surface of the cap plate, and an inner insulator on an inner surface of the cap plate, and the outer and inner insulators may receive one of the first and second electrode terminals therethrough and electrically insulate the one of the first and second electrode terminals from the cap plate. 
         [0019]    A rechargeable battery module according to another embodiment of the present invention includes a plurality of unit cells adjacent one another, and at least one bus bar connecting unit cells of the plurality of unit cells to each other in series, wherein a unit cell of the plurality of unit cells includes a case containing an electrode assembly; a cap plate coupled to the case and sealing an opening of the case; a first electrode terminal connected to a first electrode of the electrode assembly and electrically connected to the case; a second electrode terminal connected to a second electrode of the electrode assembly and electrically insulated from the case when a pressure inside the case is less than a threshold pressure; and a short-circuit unit including a short-circuit member connected to the second electrode terminal, the short-circuit unit adapted to short-circuit the second electrode terminal to the case by swelling a portion of the case to contact the short-circuit member when the pressure inside the case is equal to or greater than the threshold pressure. 
         [0020]    As such, according to an exemplary embodiment of the present invention, an insulating layer is on an outer surface of a case, one electrode terminal is electrically connected to the case, and a short-circuit unit is adapted to short-circuit another electrode terminal and the case by swelling the case, thereby preventing or reducing overcharging. That is, since charged current is discharged by the short-circuit while charging is continuous without current interruption, an increase of voltage and temperature can be prevented or reduced. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0021]      FIG. 1  is a perspective view of a rechargeable battery module according to an exemplary embodiment of the present invention. 
           [0022]      FIG. 2A  is a cross-sectional view of a unit cell of the rechargeable battery module of  FIG. 1  taken along line II-II before operation of a short-circuit unit of the rechargeable battery module. 
           [0023]      FIG. 2B  is a cross-sectional view of a unit cell of the rechargeable battery module of  FIG. 1  taken along line II-II after operation of a short-circuit unit of the rechargeable battery module. 
           [0024]      FIG. 3  is a plan view of the rechargeable battery module of  FIG. 1 . 
           [0025]      FIG. 4A  is a cross-sectional view of a short-circuit unit of the rechargeable battery module of  FIG. 1  before operation. 
           [0026]      FIG. 4B  is a cross-sectional view of a short-circuit unit of the rechargeable battery module of  FIG. 1  after operation. 
       
    
    
     DESCRIPTION OF REFERENCE NUMERALS INDICATING SOME ELEMENTS IN THE DRAWINGS 
       [0027]      
         [0000]    
       
         
               
               
             
           
               
                   
               
             
             
               
                 10: Unit cell 
                 100: Rechargeable battery module 
               
               
                 11, 12: Positive and negative 
               
               
                 electrode terminals 
               
               
                 111, 121: Nuts 
               
               
                 13: Electrode assembly 
                 14: Case 
               
               
                 141, 142, 143, 144, 145: First to fifth 
               
               
                 surfaces of case 
               
               
                 146: Cell barrier 
                 147: Flow passage 
               
               
                 15: Cap plate 
                 151: Sealing closure 
               
               
                 152: Vent portion 
                 153: Terminal hole of cap plate 
               
               
                 16, 17: Outer and inner insulators 
                 18: Insulating layer 
               
               
                 19: Connecting member 
               
               
                 20: Bus bar 
                 21: Terminal hole of bus bar 
               
               
                 31, 32: Positive and negative 
               
               
                 electrodes 
               
               
                 31a, 32a: Uncoated region 
                 33: Separator 
               
               
                 34: Current collecting member 
                 40: Short-circuit unit 
               
               
                 41: Swelling induction unit 
                 42: Short-circuit member 
               
               
                 421: Mounting portion 
                 422: Short-circuit end 
               
               
                 43: Bracket 
                 44: Insulating member 
               
               
                 T1, T2: First and second thicknesses 
               
               
                   
               
             
          
         
       
     
       DETAILED DESCRIPTION 
       [0028]    Hereinafter, the present invention will be described more fully with reference to the accompanying drawings, in which exemplary embodiments of the invention are shown. As those skilled in the art would realize, the described embodiments may be modified in various ways, all without departing from the spirit or scope of the present invention. Accordingly, the drawings and description are to be regarded as illustrative in nature and not restrictive. Like reference numerals designate like elements throughout the specification. 
         [0029]      FIG. 1  is a perspective view of a rechargeable battery module according to an exemplary embodiment of the present invention. Referring to  FIG. 1 , a rechargeable battery module  100  according to one exemplary embodiment includes two or more unit cells  10  that are sequentially disposed adjacent to each other and one or more bus bars  20  connecting the unit cells  10  to each other in series. 
         [0030]    The bus bar  20  connects a positive electrode terminal  11  of one of the unit cells  10  with a negative electrode terminal  12  of another adjacent one of the unit cells  10  in series to form the high-output rechargeable battery module  100 . An output of the rechargeable battery module  100  is dependent on the number of unit cells  10  that are connected to each other in series. 
         [0031]      FIG. 2A  is a cross-sectional view of one of the unit cells  10  of the rechargeable battery module  100  taken along line II-II of  FIG. 1  before operation of a short-circuit unit of the rechargeable battery module, and  FIG. 2B  is a cross-sectional view of one of the unit cells  10  of the rechargeable battery module  100  taken along line II-II of  FIG. 1  after operation of a short-circuit unit of the rechargeable battery module.  FIG. 3  is a plan view of the rechargeable battery module  100 . Referring to  FIGS. 2A ,  2 B, and  3 , the unit cells  10  form the rechargeable battery module  100  that includes the positive electrode terminal  11  and the negative electrode terminal  12 . 
         [0032]    In one embodiment, each of the unit cells  10  includes an electrode assembly  13  that is connected to the positive electrode terminal  11  and the negative electrode terminal  12 , a case  14  that contains the electrode assembly  13  and is electrically connected to the positive electrode terminal  11  via a connecting member  19  (shown in  FIG. 2A ), a cap plate  15  that covers an opening formed at one side of the case  14 , an outer insulator  16  that is installed on an outer surface of the cap plate  15 , and one or more inner insulators  17  that are installed on an inner surface of the cap plate  15 . 
         [0033]    The unit cell  10 , in one embodiment, further includes an insulating layer  18  that is formed on an outer surface of the case  14 . The insulating layer  18  may be formed by an insulating sheet that is attached with an insulating material or by an insulation coated layer that is coated with an insulating material. The unit cell  10  further includes a short-circuit unit  40  configured to short-circuit the negative electrode terminal  12  to the case  14  by swelling of the case  14 , in which a portion of the case  14  swells in an overcharge condition. 
         [0034]    The electrode assembly  13  may be formed in a jelly roll shape by disposing a positive electrode  31  and a negative electrode  32  on both surfaces of a separator  33 , respectively, and winding the positive electrode  31 , the negative electrode  32 , and the separator  33  all together. 
         [0035]    Each of the positive electrode  31  and the negative electrode  32  may include a coated region where a current collector formed of a thin metal foil is coated with an active material and an uncoated region  31   a  and  32   a  where the current collector is not coated with the active material. 
         [0036]    The uncoated regions  31   a  and  32   a  are formed at side ends of the positive electrode  31  and the negative electrode  32 , respectively, in longitudinal directions of the positive electrode  31  and the negative electrode  32  and at side ends opposite to each other. The uncoated regions  31   a  and  32   a  are connected to the positive electrode terminal  11  and the negative electrode terminal  12 , respectively, through respective current collecting members  34 . 
         [0037]    The case  14  forms an entire exterior of the unit cell  10  and is made of a conductive metal such as aluminum, an aluminum alloy, or nickel-plated steel. The case  14  forms a space incorporating the electrode assembly  13 . For example, the case  14  may have a prismatic hexahedron shape. 
         [0038]    In one embodiment, the case  14  includes a pair of first and second surfaces  141  and  142  (see  FIG. 3 ), each having a substantially same area (e.g., an area formed by a length and a height of the case  14 ) and facing each other; a pair of third and fourth surfaces  143  and  144  each having a substantially same area (e.g., an area formed by a width and the height of the case  14 ) smaller than the area of the first and second surfaces  141  and  142  and facing each other at two sides between the first and second surfaces  141  and  142 ; and a fifth surface  145  at another side between the first and second surfaces  141  and  142  and having an area (e.g., an area formed by the length and the width of the case  14 ) smaller than the area of the first and second surfaces  141  and  142 . The fifth surface  145  forms a side of the case  14  opposite to an opening of the case  14 . 
         [0039]    The cap plate  15  may be formed of a thin plate and is joined to the opening formed at one side of the case  14  and seals the opening. The cap plate  15  may have an electrolyte injection opening (not shown) for injecting an electrolyte into the inside of the sealed case  14 . 
         [0040]    The electrolyte injection opening is sealed with a sealing closure  151  after injecting the electrolyte. The cap plate  15  may have a vent portion  152  cut depending on an internal pressure set to prevent explosion of the unit cell  10 . 
         [0041]    The cap plate  15  has a pair of terminal holes  153  that each receive one of the positive electrode terminal  11  and the negative electrode terminal  12  therethrough. The positive electrode terminal  11  and the negative electrode terminal  12  are joined to the terminal holes  153  of the cap plate  15  to be connected to a respective current collecting member  34  in the case  14  and be connected to the electrode assembly  13  through the current collecting member  34 . 
         [0042]    In one embodiment, the outer insulator  16  is partially inserted into the terminal hole  153  of the negative electrode terminal  12  outside of the cap plate  15  to electrically insulate the negative electrode terminal  12  from the cap plate  15 . That is, the outer insulator  16  insulates the negative electrode terminal  12  from the outer surface of the cap plate  15  and, at the same time, insulates the negative electrode terminal  12  from an inner surface of the terminal hole  153  of the cap plate  15  of the negative electrode terminal  12 . In an exemplary embodiment of the outer insulator  16 , a part corresponding to the outer surface of the cap plate  15  and a part corresponding to the inner surface of the terminal hole  153  are integrally formed, but may alternatively be formed separate from each other (not shown). 
         [0043]    The bus bar  20  is provided with a pair of terminal holes  21  that correspond to the positive electrode terminal  11  and the negative electrode terminal  12  of the adjacent unit cells  10 . The bus bar  20  is installed on the outer insulator  16  of each of the adjacent unit cells  10  by inserting the positive electrode terminal  11  and the negative electrode terminal  12  through the terminal holes  21 . Nuts  111  and  121  are joined to the positive electrode terminal  11  and the negative electrode terminal  12 , respectively, such that the bus bar  20  connects the positive electrode terminal  11  and the negative electrode terminal  12  to each other in series in a pair of unit cells  10 . In the described embodiment, the outer insulator  16  supports the bus bar  20  and is between the cap plate  15  and the bus bar  20  (see  FIG. 2A ). 
         [0044]    The inner insulators  17  are provided to correspond to the terminal holes  153  inside of the cap plate  15  and electrically insulate the current collecting members  34  from the cap plate  15  on the inner surface of the cap plate  15 . In one embodiment, each of a pair of current collecting members  34  connects the positive electrode  31  and the negative electrode  32  of the electrode assembly  13  to the positive electrode terminal  11  and the negative electrode terminal  12 , respectively. 
         [0045]    In the unit cell  10  of an exemplary embodiment, the positive electrode terminal  11  is electrically connected to the case  14  through the connecting member  19 , but the negative electrode terminal  12  and the case  14  are insulated from each other for normal operation of the unit cell  10 . The connecting member  19  may be made of conductive material such as copper or aluminum. 
         [0046]    Further, in other embodiments of the unit cell  10 , the negative electrode terminal  12  may be electrically connected to the case  14  and the positive electrode terminal  11  and the case  14  may be insulated from each other (not shown). In these embodiments, in an overcharge condition, the short-circuit unit  40  may short-circuit the positive electrode terminal  11  and the case  14  to each other. 
         [0047]    When the unit cell  10  is overcharged (see  FIGS. 2B and 4B ) and deviating from a normal operating range (see  FIGS. 2A and 4A ), the short-circuit unit  40  short-circuits the negative electrode terminal  12  to the case  14 . As a result, while current charging is continuous, the short-circuit unit  40  discharges current by electrically connecting the case  14  and the negative electrode terminal  12 , thereby preventing additional increases of voltage and temperature of the unit cell  10 . As a result, safety of the unit cell  10  from overcharge is secured. 
         [0048]    The outer insulator  16  and the inner insulator  17  insulate the negative electrode terminal  12  and the case  14  from each other, and the short-circuit unit  40  selectively short-circuits the negative electrode terminal  12  and the case  14  to each other in an overcharge condition. As such, the outer insulator  16  and the inner insulator  17  and the short-circuit unit  40  perform opposite functions. 
         [0049]    In an exemplary embodiment, the short-circuit unit  40  is formed on one surface of the case  14 , that is, either one of the third and fourth surfaces  143  and  144 , and the insulating layer  18  is formed on other surfaces of the case  14  where the short-circuit unit  40  is not formed. In one exemplary embodiment, the short-circuit unit  40  is formed on the third surface  143  of the case  14  and the insulating layer  18  is formed on the first, second, fourth, and fifth surfaces  141 ,  142 ,  144 , and  145 . The insulating layer  18  may be further formed on a part of the third surface  143  except for a part corresponding to the short-circuit unit  40  (not shown). 
         [0050]    Further, in one embodiment, either one of the first and second surfaces  141  and  142  (e.g., the first surface  141 , as shown in  FIG. 3 ) is provided with cell barriers  146  to form flow passages  147  therebetween for passage of a heat transmission medium. The cell barriers  146  extend in a first direction (e.g., along the z-axis direction of  FIG. 3 ) and are spaced from each other at a predetermined interval in a second direction (e.g., the x-axis direction of  FIG. 3 ) that crosses the z-axis direction. 
         [0051]    That is, each of the flow passages  147  is formed as a space between adjacent ones of the cell barriers  146  that are formed on the first surface  141  of one unit cell  10  of two adjacent unit cells  10  and the second surface  142  of the other unit cell  10  of the two adjacent unit cells  10 . 
         [0052]    Further, the insulating layer  18  formed on the first surface  141  is also formed on outer surfaces of the cell barriers  146  formed on the first surface  141 . The insulating layer  18  formed on the cell barriers  146  prevents the cases  14  that are electrically connected to the positive electrode terminal  11  in the adjacent unit cells  10  from being connected in series. 
         [0053]    The short-circuit unit  40 , in an exemplary embodiment, includes a swelling induction unit  41  formed on the third surface  143  of the case  14  and a short-circuit member  42 . The swelling induction unit  41  is formed on the case  14 , and the short-circuit member  42  faces the swelling induction unit  41  and is connected to the negative electrode terminal  12 . 
         [0054]      FIGS. 4A and 4B  are cross-sectional views of the short-circuit unit  40  of the rechargeable battery module  100  before and after operation (e.g., due to an overcharge condition), respectively. Referring to  FIG. 4A , the swelling induction unit  41  is formed on the third surface  143  of the case  14  and has a second thickness T 2  that is thinner than a first thickness T 1  of the surrounding portions of the third surface  143  (see also  FIG. 2A ). As a result, when an internal pressure inside the case  14  increases, the first to fifth surfaces  141  to  145 , including the portion of the third surface  143  having the first thickness T 1 , are not expanded, but the swelling induction unit  41  of the third surface  143  may be expanded, or bulged, before the other surfaces (see  FIGS. 2B and 4B ). For example, the swelling induction unit  41  is concave on an inner surface of the third surface  143  and is configured to bulge outwardly in the region having the second thickness T 2  due to the internal pressure. 
         [0055]    The short-circuit member  42  is electrically connected to the negative electrode terminal  12  at one side thereof and faces an outer surface of the swelling induction unit  41  at the other side thereof. That is, in one embodiment, the short-circuit member  42  includes a mounting portion  421  that is mounted on the negative electrode terminal  12  and a short-circuit end  422  that faces the swelling induction unit  41 , and the short-circuit member  42  is bent between the mounting portion  421  and the short-circuit end  422  (e.g., bent from a horizontal orientation at the mounting portion  421  to a vertical orientation at the short-circuit end  422 ). Therefore, when the swelling induction unit  41  is expanded, or bulged, the portion of the third surface  143  having the second thickness T 2 , that is, the swelling induction unit  41 , and the short-circuit member  42  may be electrically short-circuited to each other. That is, when the swelling induction unit  41  and the short-circuit end  422  are short-circuited to each other, each of the negative electrode terminal  12 , the mounting unit  421 , the short-circuit end  422 , and the swelling induction unit  41  are electrically connected to each other. As a result, since the swelling induction unit  41  is electrically connected to the positive electrode terminal  11  on the third surface  143  of the case  14 , the positive electrode terminal  11  and the negative electrode terminal  12  are short-circuited to each other. Accordingly, since charged current is discharged through the short-circuit member  42  even though charging is continuous in the unit cell  10 , safety against overcharge is secured. 
         [0056]    Further, the short-circuit unit  40  may include a bracket  43  and an insulating member  44 . The bracket  43  is connected to the third surface  143  of the case  14  to stably support the short-circuit end  422 , thereby preventing the short-circuit end  422  from being unnecessarily short-circuited to the swelling induction unit  41 . The insulating member  44  is interposed between the portion of the short-circuit end  422  penetrating the bracket  43  and the bracket  43  to electrically insulate the short-circuit end  422  and the bracket  43  from each other. 
         [0057]    While this invention has been described in connection with what are presently considered to be practical exemplary embodiments, it is to be understood that the invention is not limited to the disclosed embodiments, but, on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims.