Abstract:
A secondary battery including an electrode assembly and a case accommodating the electrode assembly, the case including a bottom surface, a first pair of parallel sidewalls and a second pair of parallel sidewalls, connected with the bottom surface, and a corner portion formed by an intersection of each of the first pair of parallel sidewalls and the bottom surface, the corner portion having a first radius of curvature at a first region, and a second radius of curvature different from the first radius of curvature at a second region.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims priority to and the benefit of U.S. Provisional Application No. 61/843,305, filed on Jul. 5, 2013 in the U.S. Patent and Trademark Office, the entire content of which is incorporated herein by reference. 
    
    
     1. Field 
     The embodiments of the present invention relate to a secondary battery. 
     2. Description of the Related Art 
     A voltage surge may occur to a secondary battery due to, e.g., a short circuit occurring internal or external to the electrode assembly, overcharging, or overdischarging. Excessive heat generated due to the voltage surge may cause a fire or an explosion. Therefore, it is important to test the safety of the secondary battery. 
     In safety tests on secondary batteries, the secondary batteries are tested for fires and explosions under electrical conditions, such as, cell short-circuiting, abnormal charging, overcharging and forced discharging, and under physical conditions such as, vibration and shock. Particularly, in a longitudinal compression test of a secondary battery, pressure may be abruptly applied from the outside of the secondary battery to two opposing sides of the battery can, and the safety of the battery relative to the deformation is examined. When a secondary battery is longitudinally compressed, a short circuit between an active material of a positive electrode plate and an active material of a negative electrode plate may occur due to deformation of the electrode assembly, resulting in ignition and explosion of the secondary battery. 
     SUMMARY 
     An aspect of an embodiment provides a secondary battery which can improve safety by allowing a can to be deformed in a predetermined manner during, for example, a longitudinal compression test. 
     In accordance with a first aspect of an embodiment of the present invention, a secondary battery is described, including an electrode assembly, and a case accommodating the electrode assembly, the case including a bottom surface, a first pair of parallel sidewalls having a first width and being connected with the bottom surface, a second pair of parallel sidewalls having a second width smaller than the first width and being connected with the bottom surface and a corner portion formed by an intersection of each of the first pair of parallel sidewalls and the bottom surface, the corner portion having a first radius of curvature at a first region, and a second radius of curvature different from the first radius of curvature at a second region. 
     The corner portion may include an inner corner portion formed at an interior of the case and an outer corner portion formed at an exterior of the case, and wherein a radius of curvature of the inner corner portion at the first region is different from a radius of curvature of the outer corner portion at the first region. 
     The radius of curvature of the inner corner portion may be greater than the radius of curvature of the outer corner portion. 
     The radius of curvature of the inner corner portion may be less than the radius of curvature of the outer corner portion. 
     The inner corner portion may form a recessed portion in the bottom surface at the first region. 
     The recessed portion may include a stepped surface. 
     The first radius of curvature may be greater than the second radius of curvature, and may form a groove at the first region. 
     A thickness of the bottom surface at the first region may be about 65% to about 95% of a thickness of the bottom surface at the second region. 
     The corner portion may include two second regions and the first region may be located between the two second regions. 
     The first region may extend along about 1% to about 35% of the first width. 
     The corner portion may include an inner corner portion formed at an interior of the case and an outer corner portion formed at an exterior of the case, and the radius of curvature of the inner corner portion at the first region may be substantially equal to the radius of curvature of the outer corner portion at the first region. 
     The corner portion may include an inner corner portion formed at an interior of the case and an outer corner portion formed at an exterior of the case, and the radius of curvature of the outer corner portion at the first and the second region is substantially equal to the radius of curvature of the inner corner portion at the second region. 
     The corner portion may include an inner corner portion formed at an interior of the case and an outer corner portion formed at an exterior of the case, and the radius of curvature of the inner corner portion at the first and the second region may be substantially equal to the radius of curvature of the outer corner portion at the second region. 
     In accordance with a second aspect of an embodiment of the present invention, a secondary battery is described including an electrode assembly, and a case accommodating the electrode assembly, the case including a pair of longer side surfaces, a pair of shorter side surfaces, and a bottom portion connecting the pair of longer side surfaces and the pair of shorter side surfaces a cap assembly coupled to a top portion of the case, and a notched region formed at each corner portion formed where each of the pair of longer side surfaces and the bottom portion are coupled. 
     The notched region may be formed at a center region of the corner portion along each of the pair of longer side surfaces. 
     The corner portion may include an inner corner portion on an inner surface of the case and an outer corner portion on an outer surface of the case. 
     The notched region may be formed at the inner corner portion, and may form a groove extending from an inner surface of each of the pair of longer side surfaces to the bottom portion. 
     The notched region may be formed at the outer corner portion, and may form a groove extending from an outer surface of each of the pair of longer side surfaces to an outer surface of the bottom portion. 
     The notched region may include a first notched region and a second notched region, the first notched region being formed at the inner corner portion and the second notched region being formed at the outer corner portion, wherein the first notched region may form an inner groove extending from an inner surface of each of the pair of longer side surfaces to an inner surface of the bottom portion, and wherein the second notched region may form an outer groove extending from an outer surface of each of the pair of longer side surfaces to an outer surface of the bottom portion. 
     Accordingly, the secondary battery according to the aspects of the embodiment of the present invention can control a short circuit of the electrode assembly, thereby improving the safety of the secondary battery. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of a secondary battery according to an embodiment of the present invention; 
         FIG. 2  is an exploded perspective view of the secondary battery shown in  FIG. 1 ; 
         FIG. 3 a    is a sectional view taken along line I-I′ of  FIG. 1  and  FIG. 3 b    is a sectional view taken along line II-II′ of  FIG. 1 ; 
         FIG. 4  is a perspective view of a secondary battery according to another embodiment of the present invention; 
         FIG. 5  is a sectional view taken along line III-III′ of  FIG. 4 ; 
         FIG. 6  is a sectional view illustrating a deformed part according to another embodiment; and 
         FIG. 7 a    is a plan view of the secondary battery shown in  FIG. 1 . 
         FIG. 7 b    is a plan view illustrating a state in which the secondary battery shown in  FIG. 1  is longitudinally compressed. 
     
    
    
     DETAILED DESCRIPTION 
     Example embodiments of the present invention will now be described in more detail with reference to accompanying drawings, such that those skilled in the art can easily practice the present invention. 
       FIG. 1  is a perspective view of a secondary battery according to an embodiment of the present invention.  FIG. 2  is an exploded perspective view of the secondary battery shown in  FIG. 1 .  FIG. 3 a    is a sectional view taken along line I-I′ of  FIG. 1 .  FIG. 3 b    is a sectional view taken along line II-II′ of  FIG. 1 . 
     Referring to  FIGS. 1 and 2 , the secondary battery according to the embodiment of the present invention includes an electrode assembly  110 , a can  120  (also referred to as a “case” herein and used interchangeably), a cap assembly  130  and a deformed part  140 . 
     The electrode assembly  110  includes a positive electrode plate  111  having a positive electrode collector coated with a positive electrode active material, a negative electrode plate  112  having a negative electrode collector coated with a negative electrode active material, and a separator  113  interposed between the positive electrode plate  111  and the negative electrode plate  112  to electrically insulate the positive and negative electrode plates  111  and  112 . The electrode assembly  110  is formed by winding the positive electrode plate  111 , the negative electrode plate  112  and the separator  113  in a configuration similar to a jelly roll. Here, the positive electrode plate  111  may be formed of an aluminum (Al) foil, the negative electrode plate  112  may be formed of a copper (Cu) foil, and the separator  113  may be formed of polyethylene (PE) or polypropylene (PP), but the embodiments of the present invention are not limited to the materials of the positive and negative electrode plates  111  and  112  and the separator  113  listed herein. In addition, a positive electrode tab  114  is coupled to the positive electrode plate  111  to protrude upward from a top portion of the electrode assembly  110 , and a negative electrode tab  115  is coupled to the negative electrode plate  112  to protrude upward from the top portion of the electrode assembly  110 . 
     The can  120  may have a substantially hexahedron shape with an opening  120   a  through which the electrode assembly  110  is accommodated. In more detail, the can  120  includes a pair of long side surfaces  121  facing each other and having relatively large areas, a pair of short side surfaces  122  facing each other and having relatively small areas, and a bottom surface  123  coupling the pair of long side surfaces  121  and the pair of short side surfaces  122 . Here, the pair of “long” side surfaces means that it is longer with respect to the pair of “short” side surfaces, and the pair of “short” side surfaces means that it is shorter with respect to the pair of “long” side surfaces. Here, a portion of the can  120 , where the pair of long side surfaces  121  and the bottom surface  123  meet, is defined as a corner portion C. The corner portion C includes a substantially centrally positioned first region A 1  and a second region A 2  positioned at its edge. The deformed part  140  is formed in the first region A 1 . The corner portion C will later be described in more detail. 
     According to an embodiment, the can  120  is formed by a deep drawing method. Therefore, the pair of long side surfaces  121 , the pair of short side surfaces  122 , and the bottom surface  123  are integrally formed. As shown in  FIGS. 3 a  and 3 b   , the bottom surface  123  of the can  120  may be formed to be thicker than the thickness of the long side surface 121  and the short side surface  122 . In some embodiments, the can  120  is made of aluminum or an aluminum alloy, which is light in weight and ductile. In addition, the inner surface of the case  120  may be treated to be insulated from the electrode assembly  110 . 
     The cap assembly  130  is coupled to the opening  120   a  of the can  120 . In some embodiments, the cap assembly  130  includes an electrode terminal  131 , a gasket  132 , a cap plate  133 , an insulating plate  134 , a terminal plate  135  and an insulation case  136 . 
     The gasket  132  is placed between the electrode terminal  131  and the cap plate  133 , and the electrode terminal  131  and the terminal plate  135  are electrically coupled to each other. The insulating plate  134  insulates the cap plate  133  from the terminal plate  135 . An electrolyte injection hole  133   a  is formed at one side of the cap plate  133 . In order to seal the electrolyte injection hole  133   a  after an electrolytic solution is inserted into the electrolyte injection hole  133   a , a plug is installed in the electrolyte injection hole  133   a . A safety vent configured to be opened to release internal gas when the internal pressure of the can  120  exceeds a preset pressure may be formed at the other side of the cap plate  133 . The insulation case  136 , which is formed in the opening  120   a  of the can  120 , seals the can  120 . The insulation case  136  may be made of a polymer resin having an insulating property, e.g., polypropylene (PP). Holes  136   a  and  136   b  are formed in the insulation case  136  and correspond to the location of the positive electrode tab  114  and the negative electrode tab  115  to allow the positive electrode tab  114  and the negative electrode tab  115  to pass through the holes  136   a  and  136   b . In addition, an electrolyte passing hole  136   c  is formed in the insulation case  136  to be located to correspond to the electrolyte injection hole  133   a.    
     The deformed part  140  is formed at the center of the corner portion C of the can  120  to allow the can  120  to be deformed in a predetermined direction during a longitudinal compression test. That is, because a longitudinal axis of the long side surface 121  formed along the deformed part  140  serves as a central axis during the longitudinal compression test, the can  120  may be deformed by the deformed part  140  in a predetermined direction. Here, in the longitudinal compression test of a secondary battery, pressure may be applied from the pair of short side surfaces  122  of the can  120  toward the center (as shown in  FIG. 7B ), and the safety of the secondary battery  100  is examined. In addition, because the deformed part  140  is formed at the center of opposite sides of the corner portion C, where the pair of long side surfaces  121  and the bottom surface  123  meet, a position of the central axis at which the can  120  is deformed during the longitudinal compression test can be more securely defined, so that when the can  120  is longitudinally compressed, the can  120  will deform along the central axis defined by the deformed part  140 . Here, the can  120  may be deformed in opposite directions in view of the central axis. That is, referring to  FIG. 2 , the can  120  may be deformed such that the long side surface  121  positioned at the front of the can  120  (as illustrated in  FIG. 2 ) or the long side surface  121  positioned at the rear of the can  120  (as illustrated in  FIG. 2 ) get closer to each other. As described above, a short circuit of the electrode assembly  110  is controlled by allowing the can  120  to deform in a predetermined direction during the longitudinal compression test, thereby improving the safety of the secondary battery  100 . Referring to  FIGS. 3 a  and 3 b    according to an embodiment, the deformed part  140  is formed in the first region A 1  of the corner portion C of the can  120 . The corner portion C may include an inner corner C 1  formed on the inner surface of the can  120  and an outer corner C 2  formed on the outer surface of the can  120 . The deformed part  140  is formed by forming a groove  141  from the inner corner CI to the bottom surface  123 . Therefore, a thickness of the bottom surface  123  at the deformed part  140  is smaller than a thickness of the bottom surface  123  at a region around the deformed part  140  (e.g., second region A 2 ). In some embodiments, a stepped surface  142  is formed at a portion where the deformed part  140  and the bottom surface  123  meet. Here, a thickness of the bottom surface  123  may be, for example, approximately 0.5 mm, and a thickness of the bottom surface at the deformed part  140  having the stepped surface  142  may be, for example, approximately 0.4 mm. If the thickness of the deformed part  140  is larger than approximately 0.4 mm, there is no significant difference between the thicknesses of the deformed part  140  and the bottom surface  123 . Therefore, during the longitudinal compression test, it is not possible (or may be difficult) to cause the can  120  to be deformed in a predetermined direction in view of the deformed part  140 . In addition, if the thickness of the deformed part  140  is less than approximately 0.4 mm, the can  120  may be easily deformed due to a minor external shock. Therefore, the thickness of the deformed part  140  is preferably approximately 65% to 95%, and preferably approximately 80%, of the thickness of the bottom surface  123 . 
     In some embodiments, an inner radius of curvature R 1  of the deformed part  140  (first region A 1 ) is made to be greater than an inner radius of curvature R 2  of the second region A 2  of the corner portion C (R 1 &gt;R 2 ). In addition, the inner radius of curvature R 1  of the deformed part  140  is made to be greater than an outer radius of curvature R 3  of the deformed part  140  (R 1 &gt;R 3 ). Here, the inner radius of curvature R 2  of the second region A 2  is equal to the outer radius of curvature R 3  of the deformed part  140  (R 2 =R 3 ). That is, the deformed part  140  is formed such that the inner radius of curvature R 1  of the deformed part  140  and the outer radius of curvature R 3  are different from each other, and the inner radius of curvature R 1  of the deformed part  140  is greater than the outer radius of curvature R 3 . 
     In some embodiments, a length L 1  of the first region A 1  having the deformed part  140  is approximately 1% to 35%, preferably approximately 15%, of an overall length L 2  of the bottom surface  123 . For example, if the overall length L 2  of the bottom surface  123  is 51 mm, the length L 1  of the deformed part  140  is approximately 1 mm to 18 mm, preferably approximately 8 mm. Here, if the length L 1  of the deformed part  140  is less than about 1% of the overall length L 2  of the bottom surface  123 , it is not enough to deform the can  120  with respect to the deformed part  140  during the longitudinal compression test. Therefore, the can  120  may not deform in the predetermined direction. On the other hand, if the length of the deformed part  140  exceeds 35% of the overall length L 2  of the bottom surface  123 , the can  120  may deform in many directions in the deformed part  140  during the longitudinal compression test. Accordingly, it is not possible (or may be difficult) to allow the can  120  to deform in the predetermined direction. 
     As described in the embodiment above, the secondary battery  100  according to the embodiment of the present invention includes the deformed part  140  having its inner radius of curvature R 1  greater than its outer radius of curvature R 3  formed at the center of the corner portion C, where the long side surfaces  121  and the bottom surface  123  of the can  120  meet, thereby allowing the can  120  to be deformed in the predetermined direction during the longitudinal compression test. Thus, the secondary battery  100  according to the embodiment of the present invention can control a short circuit of the electrode assembly  110 , thereby improving the safety of the secondary battery  100 . 
       FIG. 4  is a perspective view of a secondary battery according to another embodiment of the present invention, and  FIG. 5  is a sectional view taken along line III-III′ of  FIG. 4 . 
     The secondary battery  200  shown in  FIG. 4  is substantially the same as the secondary battery  100  shown in  FIG. 1 , except for the configuration of the deformed part  140 . Thus, the following description will focus on the deformed part  240  shown in  FIG. 4 . 
     Referring to  FIGS. 4 and 5 , the secondary battery  200  according to another embodiment of the present invention includes an electrode assembly  110 , a can  120 , a cap assembly  130  and the deformed part  240 . 
     According to the embodiment, the deformed part  240  is formed in a first region A 1  of a corner portion C of the can  120 . The corner portion C includes an inner corner C 1  formed on an inner surface of the can  120  and an outer corner C 2  formed on an outer surface of the can  120 . The deformed part  240  is formed by forming a curved portion such that the outer corner C 2  is recessed toward the inner corner C 1 . In addition, when viewed from the outside of the can  120 , the deformed part  240  is formed to be recessed toward the inside of the can  120 . Therefore, the thickness of the corner portion C at the deformed part  240  is smaller than a thickness of the corner portion C around the deformed part  240 . 
     In some embodiments, an outer radius of curvature R 11  of the deformed part  240  is made to be greater than an outer radius of curvature R 13  of the second region A 2  of the corner portion C (R 11 &gt;R 13 ). In addition, the outer radius of curvature R 11  of the deformed part  240  is made to be greater than an inner radius of curvature R 12  of the deformed part  240  (R 11 &gt;R 12 ). Here, the outer radius of curvature R 13  of the second region A 2  is equal to the inner radius of curvature R 12  of the first region A 1  and the second region A 2  (R 13 =R 12 ). That is, the deformed part  240  is formed such that the inner radius of curvature R 12  and the outer radius of curvature R 11  are different from each other at the first region A 1 , and the outer radius of curvature R 11  at the first region A 1  is greater than the inner radius of curvature R 12  at the first region A 1  and the second region A 2 . 
     As described above, the secondary battery  200  according to an embodiment of the present invention includes the deformed part  240  having its outer radius of curvature R 11  greater than its inner radius of curvature R 12  formed at the center of the corner portion C, where the long side surfaces  121  and the bottom surface  123  of the can  120  meet, thereby allowing the can  120  to be deformed in the predetermined direction during the longitudinal compression test. Accordingly, the secondary battery  200  according to an embodiment of the present invention can control a short circuit of the electrode assembly  110 , thereby improving the safety of the secondary battery  200 . 
       FIG. 6  is a sectional view illustrating a deformed part according to another embodiment. Here, the sectional view of  FIG. 6  illustrates a part corresponding to the sectional view of  FIG. 5 . 
     Referring to  FIG. 6 , the deformed part  340  is formed at a first region A 1  of the corner portion C of the can  120 . The corner portion C includes an inner corner C 1  formed at an inner surface of the can  120  and an outer corner C 2  formed at an outer surface of the can  120 . In more detail, the deformed part  340  includes a groove  341  from the inner corner C 1  to a bottom surface  123  and a curved portion  342  recessed from the outer corner C 2  toward the inner corner C 1 . That is, the deformed part  340  is a combination of the deformed part  140  shown in  FIG. 3 a    and the deformed part  240  shown in  FIG. 5 . 
     According to an embodiment, an inner radius of curvature R 1  of the deformed part  340  is made to be greater than an inner radius of curvature R 2  of the second region A 2  of the corner portion C (R 1 &gt;R 2 ). In addition, an outer radius of curvature R 11  of the deformed part  340  is made to be greater than an outer radius of curvature R 13  of the second region A 2  of the corner portion C (R 11 &gt;R 13 ). Here, the inner radius of curvature R 1  of the deformed part  340  is equal to the outer radius of curvature R 11  of the deformed part  340  (R 1 =R 11 ), and the inner radius of curvature R 2  of the second region A 2  is equal to the outer radius of curvature R 13  of the second region A 2  (R 2 =R 13 ). That is, the deformed part  340  is formed such that the inner radius of curvature R 1  is equal to the outer radius of curvature R 11  and the inner/outer radius of curvatures R 1  and R 11  of the deformed part  340  are greater than inner/outer radius of curvatures R 2  and R 13  of the second region A 2 , respectively. 
       FIG. 7 a    is a plan view of the secondary battery shown in  FIG. 1 .  FIG. 7B  is a plan view illustrating a state in which the secondary battery shown in  FIG. 1  is longitudinally compressed. 
     Referring to  FIGS. 7 a  and 7 b   , in the secondary battery  100  according to an embodiment of the present invention, the electrode terminal  131  is electrically coupled to the terminal plate  135 , and is insulated from the cap plate  133  by the gasket  132 . The cap plate  133  is electrically coupled to the can  120 . In addition, the terminal plate  135  is spaced from the pair of long side surfaces  121  and the pair of short side surfaces  122 . That is, the electrode terminal  131  and the terminal plate  135  have the same polarity (e.g., a negative polarity), and the cap plate  133  and the can  120  have the opposite polarity (e.g., a positive polarity). 
     In such a state, if a pressure is applied from each of the pair of short side surfaces  122  toward the center of the can  120  to perform, for example, a longitudinal compression test, the can  120  is deformed at the deformed part  140  formed on the long side surface  121  as the central axis of the deformation as shown in  FIG. 7 b   . Here, the terminal plate  135  is shorted (e.g., short-circuit) to the long side surface  121  of the can  120 , so that a discharge of current is rapidly performed, thereby preventing an accident of the secondary battery  100 , such as ignition or explosion, due to over-heating of the electrode assembly  110 . As described above, because the deformed part  140  allows the can  120  to be deformed in a predetermined direction during a longitudinal compression test, short-circuiting of the electrode assembly  110  can be controlled, thereby improving the safety of the secondary battery  100 . 
     While the secondary battery of the invention has been described in connection with various example embodiments, it will be understood by those skilled in the art that the invention is not limited to the disclosed embodiments, but rather, is intended to cover various modifications included within the spirit and scope of the appended claims and equivalents thereof. 
     
       
         
               
             
               
               
               
             
           
               
                   
               
               
                 Explanation of Reference Numerals 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                   
                 100: Secondary battery 
                 110: Electrode assembly 
               
               
                   
                 120: Can (or case) 
                 121: Long side surface 
               
               
                   
                 122: Short side surface 
                 123: Bottom surface 
               
               
                   
                 130: Cap assembly 
                 140, 240, 340: Deformed part