Abstract:
A secondary battery including a can having enhanced safety against compression. A secondary battery includes: an electrode assembly; a can containing the electrode assembly and including a plate, and a wall extending from the plate in a first direction to define a cavity and an opening opposite the plate, a portion of the wall being thicker than another portion of the wall; and a cap assembly sealing the electrode assembly in the can.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims priority to and the benefit of U.S. Provisional Patent Application No. 61/163,364 filed on Mar. 25, 2009, the entire content of which is incorporated herein by reference. 
    
    
     BACKGROUND 
     1. Field 
     The present invention relates to a secondary battery. 
     2. Description of the Related Art 
     A prismatic type secondary battery includes an electrode assembly in which a positive electrode, a negative electrode, and a separator interposed between the electrodes are wound to have a jelly-roll configuration is accommodated in a can together with an electrolyte, and is finished by sealing a top opening of the can with a cap assembly. 
     Here, the can is a container formed of a conductive metal and has a box-like shape. The can is formed by a machining method such as deep drawing such that it has a bottom plate and a side wall extending along the bottom plate. The side wall has two wide side walls facing each other and two narrow side walls having a width narrower than that of the wide side walls and facing each other. An existing side wall has the same thickness along its entire sides. 
     SUMMARY 
     Embodiments of the present invention provide a secondary battery that is configured to resist compression. 
     According to one exemplary embodiment, a secondary battery includes: an electrode assembly; a can containing the electrode assembly and including a plate, and a wall extending from the plate in a first direction to define a cavity and an opening opposite the plate, a portion of the wall being thicker than another portion of the wall; and a cap assembly sealing the electrode assembly in the can. 
     The wall may include first and second walls that face each other and third and fourth walls that face each other, each of the third and fourth walls connecting the first and second walls to each other. Each of the first and second walls may have a planar shape, and each of the third and fourth walls may have a convex shape or a planar shape. 
     Each of the first and second walls may have an area greater than an area of each of the third and fourth walls. The thicker portion of the wall may include a portion of the third wall extending in the first direction and being proximate the first wall. The thicker portion of the wall further may include a portion of the fourth wall extending in the first direction and being proximate the second wall. 
     The thicker portion of the wall may further include at least a portion of the first wall proximate the third wall. The thicker portion may further include at least a portion of the second wall proximate the fourth wall and a portion of the fourth wall proximate the second wall. 
     The thicker portion may include the first wall, the second wall, the fourth wall, and at least a portion of the third wall proximate the first wall. 
     The thicker portion of the wall may include a first corner portion between the first wall and the third wall, and a second corner portion between the second wall and the fourth wall. Each of the first and second walls may have a planar shape, and each of the third and fourth walls may have a planar shape and be substantially perpendicular to each of the first and second walls. 
     The thicker portion of the wall may include a portion of the wall protruding inward toward the cavity. The protruding portion of the wall may have at least one rounded edge. 
     A thickness of the wall may be between about 0.18 mm and about 0.4 mm. 
     A difference between a thickness of the thicker portion of the wall and a thickness of the another portion of the wall may be at least 0.05 mm. 
     The thicker portion of the wall may extend in the first direction from the plate to an end proximate the opening. 
     The wall may include a stepped portion at an end of the thicker portion of the wall proximate the opening, and the cap assembly may be coupled to the can on the stepped portion. 
     According to embodiments of the present invention, since the thicknesses of two portions of one short side wall of the can are different, a force may be applied mainly to the thinner portion during compression. Accordingly, a secondary battery according to embodiments of the present invention avoids or resists compression as it is rotated, thereby enhancing safety. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Features and aspects of the present invention will be more apparent from the following detailed description in conjunction with the accompanying drawings, in which: 
         FIG. 1  is an exploded perspective view of a secondary battery according to an exemplary embodiment of the present invention; 
         FIG. 2  is a plan view of a can of the secondary battery of  FIG. 1 ; 
         FIG. 3  is a bottom view of the can of  FIG. 1 ; 
         FIG. 4  is a sectional view of the can taken along line A-A of  FIG. 2 ; 
         FIG. 5  is a sectional view of the can of  FIG. 2  viewed from the top; 
         FIG. 6  is a sectional view of a can of a secondary battery according to another exemplary embodiment of the present invention viewed from the top; 
         FIG. 7  is a sectional view of a can of a secondary battery according to yet another exemplary embodiment of the present invention viewed from the top; 
         FIG. 8  is a sectional view of a can of a secondary battery according to still another exemplary embodiment of the present invention viewed from the top; and 
         FIG. 9  is a sectional view of a can of a secondary battery according to still another exemplary embodiment of the present invention viewed from the top. 
     
    
    
     DETAILED DESCRIPTION 
     Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings. 
     According to embodiments of the present invention, a secondary battery is configured to resist compression (e.g., longitudinal compression) from the two narrow side walls that is applied to the secondary battery including the existing can to avoid a safety problem such as ignition or explosion due to the electrode assembly being popped out or short-circuited due to deformation of the can. 
     According to an embodiment of the present invention, a secondary battery includes an electrode assembly, and a can that has a bottom plate and a side wall having first and second wide side walls facing each other, first and second narrow side walls facing each other and that accommodates the electrode assembly. In some embodiments, the thickness of a first wall portion of the first narrow side wall closer to the first wide side wall is asymmetrical to a second wall portion of the first narrow side wall closer to the second wide side wall. 
       FIG. 1  is an exploded perspective view of a secondary battery according to an exemplary embodiment of the present invention.  FIG. 2  is a plan view of a can of the secondary battery of  FIG. 1 .  FIG. 3  is a bottom view of the can of  FIG. 1 .  FIG. 4  is a sectional view of the can taken along line A-A of  FIG. 2 .  FIG. 5  is a sectional view of the can of  FIG. 2  viewed from the top. 
     Referring to  FIGS. 1-5 , a secondary battery  100  according to an exemplary embodiment of the present invention includes an electrode assembly  110 , a can  120 , a cap assembly  130 , and an insulation case  140 . 
     The electrode assembly  110  includes a first electrode plate  111 , a second electrode plate  112 , and a separator  113  interposed between the electrode plates  111  and  112 , which are wound to have a jelly-roll configuration. A first conductive electrode tab  114  is coupled to the first electrode plate  111  and protrudes to the upper side of the electrode assembly  110 . A second conductive electrode tab  115  is coupled to the second electrode plate  112  and protrudes to the upper side of the electrode assembly  110 . In one embodiment of the present invention, the first electrode plate  111  is a negative electrode plate coated with a negative electrode active material and the second electrode plate  112  is a positive electrode plate coated with a positive electrode active material. However, embodiments of the present invention are not limited thereto. For example, the first electrode plate  111  may be a positive electrode plate and the second electrode plate  112  may be a negative electrode plate. Accordingly, the first electrode tab  114  may be a positive electrode tab and the second electrode tab  115  may be a negative electrode tab. 
     In some embodiments of the present invention, the two electrode tabs  114  and  115  are made of nickel, but other embodiments of the present invention are not limited thereto. 
     The can  120  has a bottom plate  121  and a side wall extending upward from the edges of the bottom plate  121 . The electrode assembly  110  is received into the can  120  through a top opening of the side wall  124 . The can  120  may be formed of a conductive metal such as aluminum, for example, by deep drawing. 
     In one embodiment, the bottom plate  121  has a bar shape that extends lengthwise along the X-axis extending longitudinally. The bottom plate  121  has a first long edge  122   a  and a second long edge  122   b  extending in parallel to each other along the X-axis and two short edges  123   a  and  123   b  shorter than the two long edges  122   a  and  122   b  and connecting ends of the two long edges  122   a  and  122   b . The two short edges  123   a  and  123   b  are rounded such that the centers thereof protrude outward. The bottom plate  121 , in one embodiment, has a thickness of 0.2 to 0.7 mm. 
     The side wall  124  has first and second wide side walls  125  and  126  facing each other and first and second narrow side walls  127  and  128  facing each other and having a width narrower than that of the wide side walls  125  and  126 . The side wall  124 , in one embodiment, has a thickness of 0.18 to 0.4 mm. If the thickness of the side wall  124  is below 0.18 mm, it may be easily deformed during an assembling process or a size test due to its weak strength, damaging the electrode assembly  110 . On the other hand, if the thickness of the side wall  124  is above 0.4 mm, the size of the electrode assembly  110  is reduced, lowering the capacity of the battery itself. 
     The first wide side wall  125  extends upward from the first long edge  122   a  of the bottom plate  121  and the second wide side wall  126  extends upward from the second long edge  122   b  of the bottom plate  121 . The first narrow wall  127  extends upward from the first short edge  123   a  of the bottom plate  121  and the second narrow wall  128  extends upward from the second short edge  123   b  of the bottom plate  121 . The two narrow side walls  127  and  128  connect the two wide side walls  125  and  126  to each other. The two narrow side walls  127  and  128  are rounded such that the centers thereof protrude outward. 
     The first narrow side wall  127  has a first wall portion  127   b  closer to the first wide side wall  125  with respect to a first center  127   a , i.e. a first protruding end and a second wall portion  127   c  closer to the second wide side wall  126 . At least one portion of the inner wall of the first wall portion  127   b  protrudes inward, the first wall portion  127   b  and the second wall portion  127   c  being asymmetrical to each other. The thickness t 1  of the first wall portion  127   b  is thicker than the thickness t 2  of the second wall portion  127   c . The thickness t 2  of the second wall portion  127   c  is substantially the same as that of the second wide side wall  126 . The protruding corner  127   b   1  of the first wall portion  127   b  may be rounded to prevent damage to the electrode assembly  110 . The second narrow side wall  128  has a third wall portion  128   b  closer to the first wide side wall  125  with respect to a second center  128   a , i.e. a second protruding end and a fourth wall portion  128   c  closer to the second wide side wall  126 . At least one portion of the inner wall of the first wall portion  127  protrudes inward, the thickness t 4  of the fourth wall portion  128   c  being thicker than the thickness t 3  of the third wall portion  128   b . The thickness t 3  of the third wall portion  128   b  is substantially the same as that of the first wide side wall  125 . Since the first wall portion  127   b  is thicker than the second wall portion  127   c , the first wall portion  127   b  is structurally reinforced as compared with the second wall portion  127   c . Since the fourth wall portion  128   c  is thicker than the third wall portion  128   b , the fourth wall portion  128   c  is structurally reinforced as compared with the third wall portion  128   b . Accordingly, when a longitudinally compressive force F is applied, a greater force, or stress, is applied to the second wall portion  127   c  than to the first wall portion  127   b  of the first narrow wall  127  and a greater force, or stress, is applied to the third wall portion  128   b  than to the fourth wall portion  128   c  of the second narrow wall  128 . The unbalance of the forces rotates the can  120  in the direction of the dotted arrow as illustrated in  FIG. 5 . Accordingly, the can  120  avoids, or resists, the longitudinal compression, thereby enhancing safety. In one embodiment, the thickness difference t 1 -t 2  between the first wall portion  127   b  and the second wall portion  127   c  and the thickness difference t 4 -t 3  between the fourth wall portion  128   c  and the third wall portion  128   b  are at least 0.05 mm, which thickness may be preferable. If the thickness differences t 1 -t 2  and t 4 -t 3  are smaller than 0.05 mm, the difference between the forces, or stresses, applied to the first wall portion  127   b  and the second wall portion  127   c  and the difference between the forces, or stresses, applied to the fourth wall portion  128   c  and the third wall portion  128   b  are not enough to rotate the can  120 . 
     Results of can testing are shown in Table 1 below. The cans tested were allowed to stand vertically and subjected to compression tests with a compression force of 13 kN applied for 2 seconds, followed by removing the compression force applied to the tested cans. Then, the outer appearances of the cans were observed. Table 1 summarizes results of experiments carried out with varying the thickness of a second wall portion of the wall portions. 
     
       
         
               
               
               
               
               
               
               
             
               
               
               
               
               
               
               
             
           
               
                   
                 TABLE 1 
               
               
                   
                   
               
               
                   
                 first wall 
                 second wall 
                 third wall 
                   
                   
                   
               
               
                   
                 portion 
                 portion 
                 portion 
                 fourth wall portion 
                 pass 
                 fail 
               
               
                   
                   
               
             
             
               
                   
               
             
          
           
               
                 Test 1 
                 0.40 mm 
                  0.2 mm 
                 0.40 mm 
                 0.40 mm 
                 10 units  
                 0 units 
               
               
                 Test 2 
                 0.40 mm 
                 0.35 mm 
                 0.40 mm 
                 0.40 mm 
                 10 units  
                 0 units 
               
               
                 Test 3 
                 0.40 mm 
                 0.36 mm 
                 0.40 mm 
                 0.40 mm 
                 8 units 
                 2 units 
               
               
                 Test 4 
                 0.40 mm 
                 0.38 mm 
                 0.40 mm 
                 0.40 mm 
                 8 units 
                 2 units 
               
               
                 Test 5 
                 0.40 mm 
                 0.40 mm 
                 0.40 mm 
                 0.40 mm 
                 8 units 
                 2 units 
               
               
                   
               
             
          
         
       
     
     As shown in Table 1, particularly in Tests 3-5, when a difference in the thickness between the second wall portion and another wall portion is less than or equal to 0.04 mm, only 8 of 10 samples were determined as “pass” and 2 samples as “fail.” In Tests 1 and 2, when the thickness difference between the second wall portion and another wall portion is at least 0.05 mm, all of 10 test samples were determined as “pass.” Thus, Table 1 shows a greater passing rate in an embodiment having a thickness difference between the second wall portion and another wall portion of greater than or equal to 0.05 mm. 
     The term “fail” used herein means to indicate that a quality problem occurred to a can. That is to say, with a compression force applied in a long axis, flames were created to heat the can, resulting in a rise of the internal temperature to about 200° C. or higher. The term “pass” used herein means to indicate that a quality problem, if any, occurred to a can is negligible. That is to say, with a compression force applied in the long-axis direction, flames or fire were created, heating the can, resulting in a problem of electrolyte leakage occurred to the can, which may insignificantly affect a state of the can. 
     First and second steps  127   e  and  128   e  are formed at the top end of the first wall portion  127   b  of the first narrow side wall  127  and the top end of the fourth wall portion  128   c  of the second narrow side wall  128 , respectively. The cap assembly  130  is positioned on the first and second steps  127   e  and  128   e.    
     The cap assembly  130  includes a cap plate  131 , a gasket  132 , an electrode terminal  133 , an insulation plate  134 , a terminal plate  135 , and a plug  137 . The cap plate  131  of the cap assembly  130  is positioned on the two steps  127   e  and  128   e  formed at the top end of the side wall  124  of the can  120  to be installed at the top opening of the can  120  and is fixed through welding. 
     The cap plate  131  has a terminal through-hole  131   a  and an electrolyte injection hole  131   b . The terminal through-hole  131   a  provides a passage through which the electrode terminal  133  is inserted. Then, the electrode terminal  133  is inserted into the terminal through-hole  131   a  with a gasket being assembled on the side wall in order to insulate the metal cap plate  131  from the metal electrode terminal  133 . Meanwhile, the electrolyte injection hole  131   b  through which an electrolyte is injected into the can  120  is formed on one side of the cap plate  131  and the electrolyte injection hole  131   b  is sealed by the plug  137  after the electrolyte is injected through the electrolyte injection hole  131   b  in order to prevent leakage of the electrolyte. 
     The insulation plate  134  is provided under the cap plate  131 . The terminal plate  135  is provided under the insulation plate  134 . Accordingly, the insulation plate  134  insulates the cap plate  131  from the terminal plate  135 . The terminal plate  135  is coupled to the bottom end of the electrode terminal  133 . Accordingly, the first electrode plate  111  of the electrode assembly  110  is electrically connected to the electrode terminal  133  through the first electrode tab  114  and the terminal plate  135 . Then, the second electrode plate  112  of the electrode assembly  110  is electrically connected to the cap plate  131  or the can  120  through the second electrode tab  115 . 
     The plug  137  is used to seal the electrolyte injection hole  131   b  after an electrolyte is injected through the electrolyte injection hole  131   b  formed in the cap plate  131 , and a ball may be pressed into the electrolyte injection hole  131   b  to seal the electrolyte injection hole  131   b  in addition to the plug  137 . 
     The insulation case  140  is provided under the terminal plate  135 . The insulation case  140  has a first electrode tab through-hole  141  through which the first electrode tab  114  is withdrawn, a second electrode tab through-hole  142  through which the second electrode tab  115  is withdrawn, and an electrolyte injection hole  143 . The insulation case  140  electrically insulates the electrode assembly  110  from the cap assembly  130 . 
     Hereinafter, a can  220  of a secondary battery according to another exemplary embodiment of the present invention will be described. 
       FIG. 6  is a sectional view of the can  220  of a secondary battery according to one exemplary embodiment of the present invention. 
     Referring to  FIG. 6 , the side wall  224  of the can  220  includes first and second wide side walls  225  and  226  facing each other and first and second narrow side walls  227  and  228  facing each other and having a width narrower than that of the two wide side walls  225  and  226 . The two narrow side walls  227  and  228  are connected to the two wide side walls  225  and  226 . The two narrow side walls  227  and  228  are rounded such that the centers thereof protrude outward. 
     The first narrow side wall  227  has a first wall portion  227   b  closer to the first wide side wall  225  and a second wall portion  227   c  closer to the second wide side wall  226 . At least one portion of the first wall portion  227   b  and the inner surface of the first wide side wall  225  protrude inward and are thicker than the second wall portion  227   c . The second narrow side wall  228  has a third wall portion  228   b  closer to the first wide side wall  225  and a fourth wall portion  228   c  closer to the second wide side wall  226 . At least one portion of the fourth wall portion  228   c  and the inner surface of the second wide side wall  226  protrude inward and are thicker than the third wall portion  228   b . Since the first wide side wall  225  and the second wide side wall  226  as well as the first wall portion  227   b  and the fourth wall portion  228   c  are thicker than the second wall portion  227   c  and the third wall portion  228   b , the can  220  avoids or resists longitudinal compression more easily due to its reinforced structure. Other aspects of the structure and operation of the can  220  are the same or similar as the embodiment illustrated in  FIGS. 1 to 5 , and a detailed description thereof will be omitted. 
     Hereinafter, a can  320  of a secondary battery according to another exemplary embodiment of the present invention will be described. 
       FIG. 7  is a sectional view of the can  320  of a secondary battery according to one exemplary embodiment of the present invention. 
     Referring to  FIG. 7 , the side wall  324  of the can  320  includes first and second wide side walls  325  and  326  facing each other and first and second narrow side walls  327  and  328  facing each other and having a width narrower than that of the two wide side walls  325  and  326 . The two narrow side walls  327  and  328  are connected to the two wide side walls  325  and  326 . The two narrow side walls  327  and  328  are rounded such that the centers thereof protrude outward. 
     The first narrow side wall  327  has a first wall portion  327   b  closer to the first wide side wall  325  and a second wall portion  327   c  closer to the second wide side wall  326 . At least one portion of the inner surface of the first wall portion  327   b  protrudes inward such that it is thicker than the second wall portion  327   c . The first wide side wall  325 , the second wide side wall  326 , and the second narrow side wall  328  have substantially the same thickness as that of the second wall portion  327   c.    
     Since the first wall portion  327   b  is thicker than the second wall portion  327   c , the first wall portion  327   b  is structurally reinforced as compared with the second wall portion  327   c . Accordingly, when a longitudinally compressive force F is applied, a greater force, or stress, is applied to the second wall portion  327   c  than to the first wall portion  327   b  of the first narrow side wall  327 . The unbalance of the force rotates the can  320  in the direction of the dotted arrow of  FIG. 7 . Accordingly, the can  320  avoids or resists the longitudinal compression, thereby enhancing safety. Other aspects of the structure and operation of the can  320  are the same or similar as the embodiment illustrated in  FIGS. 1 to 5 , and a detailed description thereof will be omitted. 
     Hereinafter, a can  420  of a secondary battery according to another exemplary embodiment of the present invention will be described. 
       FIG. 8  is a sectional view of the can  420  of the secondary battery according to one exemplary embodiment of the present invention. 
     Referring to  FIG. 8 , the side wall  424  of the can  420  includes first and second wide side walls  425  and  426  facing each other and first and second narrow side walls  427  and  428  facing each other and having a width narrower than that of the two wide side walls  425  and  426 . The two narrow side walls  427  and  428  are connected to the two wide side walls  425  and  426 . The two narrow side walls  427  and  428  are rounded such that the centers thereof protrude outward. 
     The first narrow side wall  427  has a first wall portion  427   b  closer to the first wide side wall  425  and a second wall portion  427   c  closer to the second wide side wall  426 . The first wall portion  427   b , the first wide side wall  425 , the second wide side wall  426 , and the second narrow side wall  428  have substantially the same thickness. The first wall portion  427   b  is thicker than the second wall portion  427   c.    
     Since the first wall portion  427   b  is thicker than the second wall portion  427   c , the first wall portion  427   b  is structurally reinforced as compared with the second wall portion  427   c . Accordingly, when a longitudinally compressive force F is applied, a greater force, or stress, is applied to the second wall portion  427   c  than to the first wall portion  427   b  of the first narrow side wall  427 . The unbalance of the force allows the can  420  to avoid or resist the longitudinal compression, thereby enhancing safety. Other aspects of the structure and operation of the can  420  are the same or similar as the embodiment illustrated in  FIGS. 1 to 5 , and a detailed description thereof will be omitted. 
     Hereinafter, a can  520  of a secondary battery according to another exemplary embodiment of the present invention will be described. 
       FIG. 9  is a sectional view of the can  520  of the secondary battery according to one exemplary embodiment of the present invention. 
     Referring to  FIG. 9 , the side wall  524  of the can  520  includes first and second wide side walls  525  and  526  facing each other and first and second narrow side walls  527  and  528  facing each other and having a width narrower than that of the two wide side walls  525  and  526 . The two narrow side walls  527  and  528  are connected to the two wide side walls  525  and  526 . The two narrow side walls  527  and  528  are substantially perpendicular to the two wide side walls  525  and  526  and are substantially flat. 
     The first narrow side wall  527  has a first wall portion  527   b  closer to the first wide side wall  525  and a second wall portion  527   c  closer to the second wide side wall  526 . At least one portion of the inner wall of the first wall portion  527   b  protrudes inward, the first wall portion  527   b  and the second wall portion  527   c  being different in thickness. The thickness of the second wall portion  527   c  is substantially the same as that of the second wide side wall  526 . The first narrow side wall  528  has a third wall portion  528   b  closer to the first wide side wall  525  and a fourth wall portion  528   c  closer to the second wide side wall  526 . At least one portion of the inner wall of the fourth wall portion  528   c  protrudes inward, the third wall portion  528   b  and the fourth wall portion  528   c  being different in thickness. The thickness of the third wall portion  528   b  is substantially the same as that of the first wide side wall  525 . 
     Since the first wall portion  527   b  is thicker than the second wall portion  527   c , the first wall portion  527   b  is structurally reinforced as compared with the second wall portion  527   c . Since the fourth wall portion  528   c  is thicker than the third wall portion  528   b , the fourth wall portion  528   c  is structurally reinforced as compared with the third wall portion  528   b . Accordingly, when a longitudinally compressive force F is applied, a greater force, or stress, is applied to the second wall portion  527   c  that to the first wall portion  527   b  of the first narrow wall  527  and a greater force, or stress, is applied to the third wall portion  528   b  than to the fourth wall portion  528   c  of the second narrow wall  528 . The unbalance of the forces twists the can  520 , thereby enhancing safety. Other aspects of the structure and operation of the can  520  are the same or similar as the embodiment illustrated in  FIGS. 1 to 5 , and a detailed description thereof will be omitted. 
     Although embodiments of the present invention have been described in detail herein, it should be understood that many variations and modifications of the basic inventive concept herein described fall within the spirit and scope of the present invention as defined in the appended claims.