Abstract:
A secondary battery includes a plurality of electrode assemblies; a current collector plate electrically connecting the plurality of electrode assemblies; a case accommodating the plurality of electrode assemblies; and a cap plate sealing the case, wherein the current collector plate has a resistance increasing unit thereon to increase the resistance of the current collector plate.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application claims priority to and the benefit of Korean Patent Application No. 10-2013-0043205, filed on Apr. 18, 2013, the entire content of which is incorporated herein by reference. 
       BACKGROUND 
       [0002]    1. Field 
         [0003]    Aspects of the present invention relate to a secondary battery. 
         [0004]    2. Description of the Related Art 
         [0005]    Unlike a primary battery which cannot be recharged, a secondary battery can be repeatedly charged and discharged. Low capacity batteries that use single battery cells are used as power sources for various portable small-sized electronic devices such as cellular phones, and camcorders. High power batteries that use tens of battery cells connected to each other in a battery pack are used as power sources for electric scooters, hybrid vehicles or electric vehicles. 
         [0006]    Secondary batteries may be classified into different types such as cylindrical and prismatic batteries. The secondary battery is generally configured by accommodating an electrode assembly having a positive plate and a negative plate and a separator as an insulator located therebetween in a case with an electrolyte and installing a cap plate having electrode terminals in the case. 
         [0007]    One of the evaluation tests of secondary battery safety is a nail penetration test. In the nail penetration test, a nail is allowed to penetrate in a direction in which the electrode assemblies are stacked to forcibly cause an internal short-circuit, and the extent of heat generated is investigated, thereby evaluating the safety of the secondary battery. In certain batteries, a large amount of short-circuit current is instantaneously generated due to the internal short-circuit, thereby resulting in abnormal heat generation and thermal runaway of the electrode assemblies. Accordingly, there is a demand for a secondary battery configured to improve safety of the secondary battery. 
       SUMMARY 
       [0008]    Aspects of the present invention provide a secondary battery, which can reduce the magnitude of short-circuit current or controlling the same at a constant level during a nail penetration test by forming a resistance increasing unit increasing the resistance of a current collector plate, thereby improving safety by preventing ignition and explosion of an electrode assembly. 
         [0009]    In accordance with one aspect of the present invention, there is provided a secondary battery including a plurality of electrode assemblies, a current collector plate electrically connecting the plurality of electrode assemblies, a case accommodating the plurality of electrode assemblies, and a cap plate sealing the case, wherein the current collector plate has a resistance increasing unit formed therein to increase the resistance of the current collector plate. 
         [0010]    The current collector plate may include a horizontal part positioned between the cap plate and the electrode assemblies; a vertical part bent and extending from the horizontal part, and extending parts formed at opposite sides of the vertical part, extending to a lower portion of the case and electrically connected to the electrode assemblies. 
         [0011]    Each of the vertical part may include a first region extending from the horizontal part; and a second region extending from the first region and coupled to the extending parts. 
         [0012]    The resistance increasing unit may be formed in the second region. 
         [0013]    In addition, the resistance increasing unit may pass through the second region and may be formed as an open hole having one side opened. 
         [0014]    The open hole may have a smaller width than the second region. 
         [0015]    The resistance increasing unit may be formed as a throughhole passing through the second region. 
         [0016]    The throughhole may have a smaller width than the second region. 
         [0017]    The resistance increasing unit may be formed in an uneven shape to increase a width of the second region. 
         [0018]    The plurality of electrode assemblies may include a first electrode assembly and a second electrode assembly, and the extending parts may include a front surface extending part electrically connected to the first electrode assembly and a rear surface extending part electrically connected to the second electrode assembly. 
         [0019]    The second region may connect the front surface extending part to the rear surface extending part. 
         [0020]    The case may include a bottom surface, and a pair of long side surfaces and a pair of short side surfaces upwardly extending from the bottom surface, the vertical part may be parallel to the short side surfaces, and the extending parts may be parallel to the long side surfaces. 
         [0021]    The plurality of electrode assemblies may be stacked to be parallel to the long side surface. 
         [0022]    The secondary battery may further include an electrode terminal formed to pass through the cap plate. Here, the electrode terminal is electrically connected to the horizontal part. 
         [0023]    The horizontal part may have a terminal hole to which the electrode terminal is coupled. 
         [0024]    Each of the electrode assemblies may include a first electrode plate, a second electrode plate and a separator located between the first electrode plate and the second electrode plate, and the current collector plate may be electrically connected to a first uncoated portion of the first electrode plate or a second uncoated portion of the second electrode plate. 
         [0025]    As described above, in the secondary battery according to the embodiment of the present invention, the resistance increasing unit is formed in the second region of the current collector plate connecting the first electrode assembly to the second electrode assembly, thereby reducing the magnitude of short-circuit current passing the second region and controlling the same at a constant level. Accordingly, the secondary battery according to the embodiment of the present invention may improve its safety by preventing abnormal ignition or explosion of the electrode assemblies. 
         [0026]    Additional aspects and/or advantages of the invention will be set forth in part in the description which follows and, in part, will be obvious from the description, or may be learned by practice of the invention. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0027]    The objects, features and advantages of the present invention will be more apparent from the following detailed description in conjunction with the accompanying drawings, in which: 
           [0028]      FIG. 1  is a perspective view of a secondary battery according to an embodiment of the present invention; 
           [0029]      FIG. 2  is a cross-sectional view of the secondary battery taken along the line I-I′ of  FIG. 1 ; 
           [0030]      FIG. 3  is an exploded perspective view of the secondary battery shown in  FIG. 1 ; 
           [0031]      FIG. 4  is a perspective view of a first current collector plate shown in  FIG. 1 ; 
           [0032]      FIG. 5  is a perspective view of a first current collector plate of a secondary battery according to another embodiment of the present invention, corresponding to the first current collector plate shown in  FIGS. 4 ; and 
           [0033]      FIG. 6A  is a perspective view of a first current collector plate of a secondary battery according to still another embodiment of the present invention, corresponding to the first current collector plate shown in  FIG. 4 , and  FIG. 6B  is a cross-sectional view of the secondary battery taken along the line II-II′ of  FIG. 6A . 
       
    
    
     DETAILED DESCRIPTION 
       [0034]    Hereinafter, examples of embodiments of the invention will be described in detail with reference to the accompanying drawings such that they can easily be made and used by those skilled in the art. 
         [0035]      FIG. 1  is a perspective view of a secondary battery according to an embodiment of the present invention,  FIG. 2  is a cross-sectional view of the secondary battery taken along the line I-I′ of  FIG. 1 ,  FIG. 3  is an exploded perspective view of the secondary battery shown in  FIG. 1 , and  FIG. 4  is a perspective view of a first current collector plate shown in  FIG. 1 . 
         [0036]    Referring to  FIGS. 1 to 4 , the secondary battery  100  according to an embodiment of the present invention includes electrode assemblies  110 , a first current collector plate  120 , a second current collector plate  130 , a case  140  and a cap assembly  150 . 
         [0037]    Each of the electrode assemblies  110  is formed by winding or laminating a stacked structure having a first electrode plate  111 , a separator  113  and a second electrode plate  112 , which are formed of a thin plate or layer. Here, the first electrode plate  111  may function as a negative electrode and the second electrode plate  112  may function as a positive electrode, or vice versa. In addition, the first and second electrode plates  111  and  112  may have different polarities. 
         [0038]    The first electrode plate  111  may be formed by applying a first electrode active material, such as graphite or carbon, on a first electrode collector plate formed of metal foil, such as nickel or copper foil. The first electrode plate  111  may include a first electrode uncoated portion  111   a  on which the first electrode active metal is not applied. The first electrode uncoated portion  111   a  may function as a passage for current flowing between the first electrode plate  111  and the outside of the first electrode plate  111 . However, the present invention does not limit the material of the first electrode plate  111  to those listed herein. 
         [0039]    The second electrode plate  112  may be formed by applying a second electrode active material, such as a transition metal, on a second electrode collector plate formed of such as aluminum foil. The second electrode plate  112  may include a second electrode uncoated portion  112   a  on which the second electrode active metal is not applied. The second electrode uncoated portion  112   a  may function as a passage for current flowing between the second electrode plate  112  and the outside of the second electrode plate  112 . However, the present invention does not limit the material of the second electrode plate  112  to those listed herein. 
         [0040]    The separator  113  may be located between the first electrode plate  111  and the second electrode plate  112  to prevent short circuiting and allow the movement of lithium ions. The separator  113  may be formed of, for example, polyethylene, polypropylene, or combined film of polypropylene and polyethylene. However, the present invention does not limit the material of the separator  113  to those listed herein. 
         [0041]    Each of the electrode assemblies  110  and an electrolyte are accommodated within the case  140 . The electrolyte may include an organic solvent such as ethylene carbonate (EC), propylene carbonate (PC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), or dimethyl carbonate (DMC), and a lithium salt such as LiPF 6  or LiBF 4 . The electrolyte may be a liquid, a solid, or a gel. 
         [0042]    In addition, a plurality of electrode assemblies  110  may be accommodated in the case  140 . In one embodiment, as shown in  FIG. 3 , two of the electrode assemblies  110  are accommodated in the case  140 . One electrode assembly positioned ahead in the case  140  is referred to as a first electrode assembly  110   a,  and one electrode assembly positioned behind in the case  140  is referred to as a second electrode assembly  110   b.    
         [0043]    The first current collector plate  120  may be formed of, for example, copper or a copper alloy, and may contact the first electrode uncoated portion  111   a  protruding from an end of the electrode assembly  110 . In practice, the first current collector plate  120  may be welded to the first electrode uncoated portion  111   a  to be electrically connected to the first electrode plate  111 . Referring to  FIG. 4 , the first current collector plate  120  may include a first horizontal part  121 , a first vertical part  122 , first extending parts  123  and a first resistance increasing unit  124 . 
         [0044]    The first horizontal part  121  is installed between a top portion of the electrode assemblies  110  and a bottom portion of the cap assembly  150  in the form of a plate. In detail, the first horizontal part  121  is formed to be generally parallel to a cap plate  151  of the cap assembly  150 . In addition, the first horizontal part  121  has a first terminal hole  121   a  formed therein. A first electrode terminal  152  of the cap assembly  150  may be fitted into and coupled to the first terminal hole  121   a.    
         [0045]    The first vertical part  122  is bent and extends from an end of the first horizontal part  121 . The first vertical part  122  is formed to be generally perpendicular to the first horizontal part  121  and the cap plate  151  and is formed to be generally parallel to a side surface  142  of the case  140 . In particular, the first vertical part  122  is formed to be generally parallel to short side surfaces  142   c  and  142   d  of the case  140 . 
         [0046]    The first vertical part  122  includes a first region  122   a  and a second region  122   b.  The first region  122   a  is a part connected to the first horizontal part  121 , and the second region  122   b  is a region downwardly extending from the first region  122   a.  In addition, the first extending parts  123  are coupled to the second region  122   b.  In practice, the second region  122   b  serves to connect the first electrode assembly  110   a  to the second electrode assembly  110   b.  In other words, the first extending parts  123  are connected to the first electrode assembly  110   a  and the second electrode assembly  110   b,  and the second region  122   b  connects the first extending parts  123  to each other. In addition, the first resistance increasing unit  124  to be described below is formed in the second region  122   a.    
         [0047]    The first extending parts  123  are positioned on both side surfaces of the first vertical part  122 . In one embodiment, the first extending parts  123  are coupled to opposite sides of the second region  122   b.  In addition, the first extending parts  123  are coupled to the overall side surface of the second region  122   b  and are formed to extend from the second region  122   b.  In addition, the first extending parts  123  are formed to be parallel to the long side surfaces  142   a  and  142   b  of the case  140  and are coupled to the first electrode uncoated portions  111  a of the electrode assemblies  110 . Therefore, each of the first extending parts  123  may be formed to have lengths equal to or smaller than those of the first electrode uncoated portions  111   a.    
         [0048]    The first extending parts  123  include a front surface extending part  123   a  and a rear surface extending part  123   b.  The front surface extending part  123   a  and the rear surface extending part  123   b  face and are opposite to each other. The front surface extending part  123   a  is coupled to the first electrode assembly  110   a,  and the rear surface extending part  123   b  is coupled to the second electrode assembly  110   b.  In detail, the first electrode uncoated portion  111   a  of the first electrode assembly  110   a  is welded to the front surface extending part  123   a,  and the first electrode uncoated portion  111  a of the second electrode assembly  110   b  is welded to the rear surface extending part  123   b.    
         [0049]    The first resistance increasing unit  124  is formed in the second region  122   b  of the first vertical part  122 . In addition, the first resistance increasing unit  124  is formed in the second region  122   b  and is formed as an open hole having one side opened, i.e., a notch. Therefore, a longitudinal width of the second region  122   b  connecting the front surface extending part  123   a  and the rear surface extending part  123   b  is reduced by the first resistance increasing unit  124 , and the resistance of the second region  122   b  may increase. In addition, a movement path of current flowing from the front surface extending part  123   a  to the rear surface extending part  123   b  narrows by the first resistance increasing unit  124 . In other words, when the first resistance increasing unit  124  is formed in the second region  122   b,  a bottleneck may occur in which the current flowing through the second region  122   b  concentrates in one direction, thereby increasing the resistance of the second region  122   b.    
         [0050]    The first resistance increasing unit  124  is formed to have a longitudinal width smaller than a width of the second region  122   b  to allow the current to flow from the front surface extending part  123   a  to the rear surface extending part  123   b.  In addition, the first resistance increasing unit  124  may be formed in any shape so long as it can reduce the longitudinal width of the second region  122   b.  For example, the first resistance increasing unit  124  may be formed of various shapes, such as a rectangle, a triangle, a circle, or an ellipse having one side opened. 
         [0051]    A nail penetration test is generally used as one of evaluation tests of secondary battery safety. In the nail penetration test, a nail is allowed to penetrate in a direction in which the electrode assemblies are stacked to forcibly generate internal short-circuit, and the extent of heat generated is investigated, thereby evaluating the safety of the secondary battery. If the internal short-circuit is caused by the nail passing through the first electrode assembly, a large amount of short-circuit current is instantaneously generated. The short-circuit current flows in to the second electrode assembly through the second region, and abnormal heat generation and thermal runaway of the electrode assemblies may occur due to the internal short-circuit current. 
         [0052]    However, in the secondary battery  100  according to the embodiment of the present invention, since the first resistance increasing unit  124  is formed in the second region  122   b  connecting the first electrode assembly  110   a  to the second electrode assembly  110   b,  the resistance of the second region  122   b  is relatively large. Therefore, the magnitude of the short-circuit current passing the second region  122   b  can be reduced or controlled to be at a constant level. Accordingly, the secondary battery  100  according to the embodiment of the present invention may have improved safety by suppressing abnormal heat generation. 
         [0053]    The second current collector plate  130  may be formed of a conductive material, for example, aluminum or an aluminum alloy, and may contact the second electrode uncoated portion  112   a  protruding from the other end of each of the electrode assemblies  110 . In practice, the second current collector plate  130  may be welded to the second electrode uncoated portion  112   a  to be electrically connected to the second electrode plate  112 . The second current collector plate  130  may include a second horizontal part  131 , a second vertical part  132 , second extending parts  133  and a second resistance increasing unit  134 . 
         [0054]    The second current collector plate  130  has substantially the same configuration as the first current collector plate  120  shown in  FIG. 4 , and repeated explanations will be omitted. 
         [0055]    The case  140  may be formed of a conductive metal, such as aluminum, an aluminum alloy or a nickel plated steel and may have an approximately hexahedron shape provided with an opening through which the electrode assemblies  110 , the first current collector plate  120  and the second current collector plate  130  are inserted and placed. Since the case  140  and the cap assembly  150  are illustrated in an assembled state in  FIG. 2 , the opening of the case  140  is not shown. However, it will be appreciated that the opening corresponds to a substantially opened portion of the edge of the cap assembly  150 . In addition, the case  140  includes a bottom surface  141  and side surfaces  142  upwardly extending from the bottom surface  141 . The side surfaces  142  include a pair of long side surfaces  142   a  and  142   b  facing each other, and a pair of short side surfaces  142   c  and  142   d  connecting the long side surfaces  142   a  and  142   b  and facing each other. In one embodiment, the inner surface of the case  140  may be treated to be insulated from the electrode assemblies  110 , the first current collector plate  120 , the second current collector plate  130  and the cap assembly  150 . In one embodiment, the case  140  may have a polarity and may serve as, for example, a positive electrode. 
         [0056]    The cap assembly  150  is coupled to the case  140 . In one embodiment, the cap assembly  150  may include the cap plate  151 , the first electrode terminal  152 , the second electrode terminal  153 , a gasket  154 , and a terminal plate  155 . In addition, the cap assembly  150  may further include a plug  156 , a vent plate  157 , a connection member  158 , an upper insulation member  159 , and a lower insulation member  160 . 
         [0057]    The cap plate  151  closes the opening of the case  140 . The cap plate  151  may be formed of the same material the case  140 . For example, the cap plate  151  may be coupled to the case  140  by laser welding. In one embodiment, the cap plate  151  and the case  140  may have the same polarity. 
         [0058]    The first electrode terminal  152  is electrically connected to the first current collector plate  120  while passing through one side of the cap plate  151 . The first electrode terminal  152  may be formed in a pillar shape. In addition, the first electrode terminal  152  upwardly protrudes and extends from the cap plate  151 , and a flange  152   a  is formed at a lower portion of the cap plate  151  to prevent the first electrode terminal  152  from being dislodged from the cap plate  151 . A region of the first electrode terminal  152  positioned under the flange  152   a  is fitted into the first terminal hole  121   a  of the first current collector plate  120 . In one embodiment, the first electrode terminal  152  is insulated from the cap plate  151 . 
         [0059]    The second electrode terminal  153  is electrically connected to the second current collector plate  130  while passing through the other side of the cap plate  151 . Since the second electrode terminal  153  has the same shape as the first electrode terminal  152 , repeated explanations will be omitted. In one embodiment, the second electrode terminal  153  may be electrically connected to the cap plate  151 . 
         [0060]    The gasket  154  may be formed of an insulating material, and may be located between the cap plate  151  and the first and second electrode terminals  152  and  153  to seal spaces between the cap plate  151  and the first and second electrode terminals  152  and  153 . The gasket  154  may prevent the introduction of moisture into the secondary battery  100  or the leakage of the electrolyte from the secondary battery  100 . 
         [0061]    The terminal plate  155  is coupled to the first electrode terminal  152  and the second electrode terminal  153 . In addition, the terminal plate  155  is welded to the first electrode terminal  152  and the second electrode terminal  153 , thereby fixing the first electrode terminal  152  and the second electrode terminal  153  to the cap plate  151 . In other words, boundary regions between each of the first electrode terminal  152  and the second electrode terminal  153 , exposed to the upper portion of the cap plate  151 , and the terminal plate  155 , are welded to each other. For example, laser beams are applied to the boundary regions between each of the upwardly exposed first and second electrode terminals  152  and  153  and the terminal plate  155 , thereby welding the boundary regions to each other by fusing and cooling. 
         [0062]    The plug  156  may close an electrolyte injection hole  151   a  of the cap plate  151 . The vent plate  157  may be installed in a vent hole  151   b  of the cap plate  151  and may have a notch  157   a  to be opened at a set pressure. 
         [0063]    The connection member  158  is formed such that the second electrode terminal  153  is fitted into a region between the second electrode terminal  153  and the cap plate  151  and makes close contact with the cap plate  151  and the gasket  154  through the terminal plate  155 . The connection member  158  is electrically connected to the second electrode terminal  153  and the cap plate  151 . 
         [0064]    The upper insulation member  159  is formed such that the first electrode terminal  152  is fitted into a region between the first electrode terminal  152  and the cap plate  151  and makes close contact with the cap plate  151  and the gasket  154  through the terminal plate  155 . The upper insulation member  159  insulates the first electrode terminal  152  and the cap plate  151  from each other. 
         [0065]    The lower insulation member  160  is formed between each of the first current collector plate  120  and the second current collector plate  130  and the cap plate  151 , thereby preventing unnecessary short-circuits. 
         [0066]    As described above, in the secondary battery  100  according to the embodiment of the present invention, the first resistance increasing unit  124  increasing the resistance of the first current collector plate  120  is formed in the second region  122   b  of the first current collector plate  120  connecting the first electrode assembly  110   a  and the second electrode assembly  110   b,  thereby reducing the magnitude of short-circuit current or controlling the same at a constant level during a nail penetration test. Accordingly, the secondary battery  100  according to the embodiment of the present invention may have improved safety by suppressing abnormal heat generation of the first and second electrode assemblies  110   a  and  110   b.    
         [0067]      FIG. 5  is a perspective view of a first current collector plate of a secondary battery according to another embodiment of the present invention, corresponding to the first current collector plate shown in  FIG. 4 . 
         [0068]    The first current collecting plate for a secondary battery shown in  FIG. 5  is substantially the same first current collecting plate  120  shown in  FIG. 4  in view of configurations and functions, except for a configuration of a first resistance increasing unit  224  of a first current collector plate  220 . Thus, repeated illustration and explanations of the same functional components will be omitted, and the following description will focus on the first resistance increasing unit  224  of the first current collector plate  220 . 
         [0069]    Referring to  FIG. 5 , the first current collector plate  220  includes a first horizontal part  121 , a first vertical part  122 , first extending parts  123  and a first resistance increasing unit  224 . 
         [0070]    The first resistance increasing unit  224  is formed in a second region  122   b  of the first vertical part  122 . In addition, the first resistance increasing unit  224  formed in the second region  122   b  is formed as a throughhole passing through the center of the second region  122   b.  Thus, a longitudinal width of the second region  122   b  connecting a front surface extending part  123   a  and a rear surface extending part  123   b  is reduced by the throughhole and the resistance of the second region  122   b  may increase. In addition, a movement path of current flowing from the front surface extending part  123   a  to the rear surface extending part  123   b  narrows by the throughhole. In other words, if the first resistance increasing unit  224  is formed in the second region  122   b  in the form of a throughhole, a bottleneck may occur, in which the current flowing through the second region  122   b  concentrates in opposite directions of the throughhole, thereby increasing the resistance of the second region  122   b.    
         [0071]      FIG. 6A  is a perspective view of a first current collector plate of a secondary battery according to still another embodiment of the present invention, corresponding to the first current collector plate shown in  FIG. 4 , and  FIG. 6B  is a cross-sectional view of the secondary battery taken along the line II-II′ of  FIG. 6A . 
         [0072]    The first current collecting plate for a secondary battery shown in  FIG. 6  is substantially the same first current collecting plate  120  shown in  FIG. 4  in view of configurations and functions, except for a configuration of a first resistance increasing unit  324  of a first current collector plate  320 . Thus, repeated illustration and explanations of the same functional components will be omitted, and the following description will focus on the first resistance increasing unit  324  of the first current collector plate  320 . 
         [0073]    Referring to  FIGS. 6A and 6B , the first current collector plate  320  includes a first horizontal part  121 , a first vertical part  122 , first extending parts  123  and the first resistance increasing unit  324 . 
         [0074]    The first resistance increasing unit  324  is formed in a second region  122   b  of the first vertical part  122 . In addition, the first resistance increasing unit  324  connects a front surface extending part- 123   a  to a rear surface extending part  123   b  and is formed in an uneven shape or a block-S pattern shape. Therefore, a horizontal width of the second region  122   b  connecting the front surface extending part  123   a  to the rear surface extending part  123   b  is effectively increased by the first resistance increasing unit  324 . In other words, since the uneven first resistance increasing unit  324  is formed in the second region  122   b,  the horizontal width of the second region  122   b  is effectively increased, and therefore the resistance of the second region  122   b  may also be increased. As described above, if the horizontal width of the second region  122   b  is increased by the first resistance increasing unit  324 , it is relatively difficult for the current to pass the second region  122   b.  Accordingly, the magnitude of short-circuit current passing the second region  122   b  can be reduced or controlled to be at a constant level. In addition, the first resistance increasing unit  324  may be formed in any shape so long as it can increase the horizontal width of the second region  122   b.    
         [0075]    Although the secondary battery according to embodiments of the present invention have been described in detail hereinabove, it should be understood that many variations and modifications of the basic inventive concept herein described, which may appear to those skilled in the art, will still fall within the spirit and scope of the exemplary embodiments of the present invention as defined by the appended claims.