Abstract:
A secondary battery includes an electrode assembly formed by winding two different electrodes and a separator interposed therebetween, a can housing the electrode assembly, a cap assembly at a upper opening of the can; and a gasket interposed between the cap assembly and the can. The gasket has a relaxed condition prior to compression between the cap assembly and an upper portion of the can and a compressed condition after compression between the cap assembly and the upper portion of the can. The gasket includes a sidewall portion bent inwardly from outside of the can when the gasket is in the compressed condition, a bottom portion at a bottom of the sidewall portion and extending inwardly from a periphery of the can, a protruding portion on which the cap assembly is seated, and a concave portion formed between the protruding portion and an inner surface of the sidewall portion.

Description:
BACKGROUND 
       [0001]    1. Field 
         [0002]    Embodiments relate to a secondary battery. 
         [0003]    2. Description of the Related Art 
         [0004]    Generally, secondary batteries are classified into cylindrical, prismatic and pouch type batteries according to the shape of a case receiving an electrode assembly. Specifically, the cylindrical secondary battery includes a cylindrical electrode assembly inserted into a cylindrical can, and a cap assembly to seal an upper opening of the cylindrical can. The cap assembly is electrically connected to the electrode assembly to allow current generated in the electrode assembly to flow to the outside. 
       SUMMARY 
       [0005]    According to an embodiment, there is provided a secondary battery including an electrode assembly formed by stacking two different electrodes and a separator interposed therebetween and winding the same, a can to house the electrode assembly, a cap assembly at a upper opening of the can, and a gasket interposed between the cap assembly and the can. The gasket has a relaxed condition prior to compression between the cap assembly and an upper portion of the can and a compressed condition after compression between the cap assembly and the upper portion of the can. The gasket includes a sidewall portion bent inwardly from outside of the can when the gasket is in the compressed condition, a bottom portion at a bottom of the sidewall portion and extending inwardly from a periphery of the can, a protruding portion on which the cap assembly is seated, and a concave portion formed between the protruding portion and an inner surface of the sidewall portion. 
         [0006]    When the gasket is in the relaxed condition, the protruding portion may protrude from the bottom portion in a direction away from a lower plate of the can, and form a tilt angle with respect to a direction parallel with the lower plate of the can. 
         [0007]    The tilt angle may be in a range from 25° to 75°. 
         [0008]    A top of the protruding portion may include a planar portion. 
         [0009]    The planar portion may have a length in a radial direction in a range from 0.1 mm to 0.25 mm. 
         [0010]    The cap assembly may include a cap up, a safety vent, and a cap down. 
         [0011]    A positive temperature coefficient (PTC) element as a secondary protective device may be further provided between the cap up and the safety vent. 
         [0012]    When the gasket is in the relaxed condition, a distance between the inner surface of the sidewall portion and the innermost part of the protruding portion may be in a range from 0.42 mm to 0.98 mm. 
         [0013]    When the gasket is in the relaxed condition, the protruding portion may have a height in a range from 0.3 mm to 0.6 mm. 
         [0014]    A reinforcement member may be further provided between the inner surface of the sidewall portion and the protruding portion. 
         [0015]    The reinforcement member may contact the inner surface of the sidewall portion and the bottom surface of the concave portion. 
         [0016]    The reinforcement member may have a top portion having a planar shape. 
         [0017]    When the gasket is in the relaxed position, a height of the reinforcement member may be in a range of ⅓ to ⅔ of a height of the protruding portion. 
         [0018]    The gasket may be made of at least one of polypropylene, polyethylene, and polyethylene terephthalate. 
         [0019]    The can that houses the electrical assembly may be cylindrical. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0020]    The above and other features and advantages will become more apparent to those of ordinary skill in the art by describing in detail exemplary embodiments with reference to the attached drawings, in which: 
           [0021]      FIG. 1  illustrates a frontal section view of a secondary battery according to an embodiment; 
           [0022]      FIG. 2  illustrates an enlarged frontal section view of a cap assembly of the secondary battery shown in  FIG. 1 ; 
           [0023]      FIG. 3A  illustrates a frontal section view of a gasket of the secondary battery shown in  FIG. 1 ; 
           [0024]      FIG. 3B  illustrates a frontal section view of a portion III of the cap assembly illustrated in  FIG. 2  in a state in which the cap assembly is yet to be crimped; 
           [0025]      FIG. 4  illustrates a frontal section view of a gasket of a secondary battery according to another embodiment; and 
           [0026]      FIG. 5  illustrates a frontal section view of a gasket of a secondary battery according to still another embodiment. 
       
    
    
     DETAILED DESCRIPTION 
       [0027]    Korean Patent Application No. 10-2010-0090919, filed on Sep. 16, 2010 in the Korean Intellectual Property Office, and entitled: “Cylindrical Secondary Battery,” is incorporated by reference herein in its entirety. 
         [0028]    Example embodiments will now be described more fully hereinafter with reference to the accompanying drawings; however, they may be embodied in different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. 
         [0029]    In the drawing figures, the dimensions of layers and regions may be exaggerated for clarity of illustration. Like reference numerals refer to like elements throughout. 
         [0030]    First, a secondary battery according to an embodiment will be described. 
         [0031]      FIG. 1  is a frontal section view of a secondary battery according to an embodiment,  FIG. 2  is an enlarged frontal section view of a cap assembly of the secondary battery shown in  FIG. 1 ,  FIG. 3A  is a frontal section view of a gasket of the secondary battery shown in  FIG. 1 , and  FIG. 3B  is a frontal section view of a portion III of the cap assembly illustrated in  FIG. 2  in a state in which the cap assembly is yet to be crimped. 
         [0032]    Referring to  FIGS. 1 and 2 , the secondary battery according to an embodiment includes a can  100 , an electrode assembly  200  inserted into the can  100 , a cap assembly  300  coupled to a upper opening of the can  100 , and a gasket  400  installed between the cap assembly  300  and an inner circumferential surface of the upper opening of the can  100 . 
         [0033]    The can  100  includes a cylindrical side plate  110  having a predetermined diameter to form a space to receive the electrode assembly  200 , and a lower plate  120  sealing a bottom portion of the side plate  110 . In addition, a beading part  130  for preventing the electrode assembly  200  from moving is formed at an upper opening of the can  100 . A crimping part  140  for fixing the cap assembly  300  is formed at the uppermost part of the cylindrical can  100 . 
         [0034]    The can  100  may be made of a lightweight conductive metal such as aluminum or an aluminum alloy. In addition, the can  100  may be formed by, for example, a deep drawing process. 
         [0035]    The electrode assembly  200  may be formed by winding into a jellyroll-type shape a positive electrode plate  210  including a positive electrode active material coated on a surface of a positive electrode collector, a negative electrode plate  220  including a negative electrode active material coated on a surface of a negative electrode collector, and a separator  230  interposed between the positive and negative electrode plates  210  and  220  and electrically connecting the positive and negative electrode plates  210  and  220  to each other. 
         [0036]    At an upper portion of the electrode assembly  200 , a positive electrode tab  240  is connected to the cap assembly  300 , and at a lower portion of the electrode assembly  200 , a negative electrode tab  250  is connected to the lower plate of the can  100 . 
         [0037]    The positive electrode collector of the positive electrode plate  210  is made of a conductive metal to collect electrons from a positive electrode coating portion to permit the collected electrons to move to an external circuit. The positive electrode coating portion may be prepared by mixing a positive electrode active material, a conductive agent, and a binder, and coating the resultant mixture on the positive electrode collector to a predetermined thickness. A positive electrode uncoated portion may be formed at both ends of the positive electrode plate  210 , where the positive electrode active material is not coated, and the positive electrode tab  240  is welded to one side of the positive electrode uncoated portion. 
         [0038]    The negative electrode collector of the negative electrode plate  220  is made of a conductive metal to collect electrons from a negative electrode coating portion to permit the collected electrons to move to an external circuit. The negative electrode coating portion may be prepared by mixing a negative electrode active material, a conductive agent, and a binder, and coating the resultant mixture on the negative electrode collector to a predetermined thickness. A negative electrode uncoated portion may be formed at both ends of the negative electrode plate  220 , where the negative electrode active material is not coated, and the negative electrode tab  250  is welded to one side of the negative electrode uncoated portion. 
         [0039]    The separator  230  is interposed between the positive electrode plate  210  and the negative electrode plate  220  and may extend to surround the outer circumferential surface of the electrode assembly  200 . The separator  230  prevents a short between the positive electrode plate  210  and the negative electrode plate  220 . The separator  230  may be made of a porous polymer material to permit lithium ions to pass therethrough. 
         [0040]    The cap assembly  300  is electrically connected to the electrode assembly  200 , and includes an upper cap portion, referred to herein as a “cap up”  310 , a safety vent  320 , a lower cap portion, referred to herein as a “cap down”  340 , an insulator  330 , and a sub plate  350 . The cap up  310  transfers the current generated from the electrode assembly  200  to the outside. The safety vent  320  contacts a lower surface of the cap up  310 . The safety vent  320  interrupts current and discharges internal gas when abnormal internal pressure is generated in the cylindrical can  100 . The cap down  340  is provided below the safety vent  320  to seal the cylindrical can  100 . The insulator  330  is interposed between the safety vent  320  and cap down  340 . The sub plate  350  is fixed to a lower surface of the cap down  340 , and the positive electrode tab  240  (cathode tab) is attached to the sub plate  350 . 
         [0041]    The cap up  310  is formed of a circular plate having a terminal part  311  that convexly projects from the center thereof and is electrically connected to an external device. A plurality of gas discharge holes  312  are formed on the outer circumferential surface of the terminal part  311  to discharge the gas generated inside the can  100 . 
         [0042]    The safety vent  320  is formed of a circular plate corresponding to that of the cap up  310 , and a protruding portion  321  protrudes downwardly in the center of the safety vent  320 . 
         [0043]    The insulator  330  is interposed between the safety vent  320  and the cap down  340  and is made of a material capable of insulating the safety vent  320  and the cap down  340  from each other. 
         [0044]    The cap down  340  is formed of a circular plate. A through-hole  341  is formed in the center of the cap down  340 . The protruding portion  321  of the safety vent  320  extends through the through-hole  341 . A gas discharge hole  342 , through which the gas raising the protruding portion  321  of the safety vent  320  is discharged when an excessive internal pressure is generated, is formed at one side of the cap down  340 . 
         [0045]    The sub plate  350  is welded to the protruding portion  321  of the safety vent  320 , which extends through the through-hole  341  of the cap down  340 , thereby electrically connecting the positive electrode tab  240  to the safety vent  320 . 
         [0046]    Although not shown, a positive temperature coefficient (PTC) element may further be provided as a secondary protective device between the cap up  310  and the safety vent  320 . The PTC element prevents the internal temperature from rising by interrupting the current when the secondary battery is overheated. 
         [0047]    The cap up  310  and the safety vent  320  are seated on the protruding portion  430  provided on the inner circumferential surface of the gasket  340  installed at the upper opening of the can  100 , to combine the gasket  400  with the outer circumferential surface of the cap up  310 . 
         [0048]    Referring to  FIGS. 3A and 3B , the gasket  400  includes a sidewall portion  410 , a bottom portion  420 , a protruding portion  430 , and a concave portion  440 . The concave portion  440  is formed between the protruding portion  430  and an inner surface  411  of the sidewall portion  410 . 
         [0049]    The gasket  400  is compressed and fixed while it is interposed between the cap assembly  300  and the can  100 . Accordingly, the gasket  400  seals a gap between the can  100  and the cap assembly  300  and insulates the can  100  and the cap assembly  300  from each other. Additionally, the gasket  400  may insulate a gap between the electrode assembly  200  and the cap assembly  300  and may absorb impacts applied from the electrode assembly  200  when the battery falls or vibrates. 
         [0050]    A top end of the sidewall portion  410  is inwardly bent from the outside of the can  100  when a crimping operation is performed, that is, when the gasket  400  is disposed between the cap assembly  300  and the upper portion of the can  100  and compressed. In a state in which the gasket  400  is inserted into the inner circumferential surface of the upper opening of the can  100 , the cap assembly  300  is seated on the protruding portion  430  and the upper portion of the can  100  is crimped. In the course of crimping the upper portion of the can  100 , the sidewall portion  410  of the gasket  400  is maintained at a close contact with the cap up  310  and the outer circumferential surface of the safety vent  320  with a predetermined compressive force. 
         [0051]    The bottom portion  420  is formed at a lower portion of the sidewall portion  410  to inwardly extend from the outside of the can  100 . The bottom portion  420  serves as a barrier against an impact that may be applied from the electrode assembly  200  or center pin of a battery to the safety vent  320  when the battery falls. 
         [0052]    The sidewall portion  410  and the bottom portion  420  may be integrally formed with each other. In addition, the sidewall portion  410  and the bottom portion  420  may be made of a material capable of absorbing shocks applied to the electrode assembly  200  or the center pin when the battery falls or vibrates. The sidewall portion  410  and the bottom portion  420  may also be made of a material capable of insulating a gap between the electrode assembly  200  and the cap assembly  300 . As a non-limiting example, the sidewall portion  410  and the bottom portion  420  may be made of a material that does not react with an electrolyte. A material that is generally used in the art in the manufacture of gaskets for batteries can be used without limitation. Non-limiting examples of the useful material of the sidewall portion  410  and the bottom portion  420  may include polypropylene, polyethylene, and polyethylene terephthalate. 
         [0053]    The protruding portion  430  protrudes from the bottom portion  420  in a direction away from the lower plate  120  of the can  100 , and forms a tilt angle θ with respect to a direction parallel with the lower plate  120  of the can  100 . A lower sidewall of the safety vent  320  forming the cap assembly  300  is seated on the protruding portion  430 . 
         [0054]    The concave portion  440  is formed between the protruding portion  430  and the inner surface  411  of the sidewall portion  410 . 
         [0055]    A distance A from the inner surface  411  of the sidewall portion  410  to the innermost part of the protruding portion  430  may be from 0.42 mm to 0.98 mm. If the distance A is less than 0.42 mm, a gap between the gasket  400  and the cap assembly  300  may be generated during a crimping process, making it difficult to maintain a predetermined compressive pressure. If the distance A is greater than 0.98 mm, an excessive compressive force may be applied to the gasket  400  during a crimping process. Here, the term “innermost part of the protruding portion  430 ” may refer to a part of the protruding portion  430  that is farthest from the inner surface  411  of the sidewall portion  410 . 
         [0056]    The protruding portion  430  may have a height B in a range from 0.3 mm to 0.6 mm. The term “height B of the protruding portion  430 ” may refer to a distance from the lowest point of the concave portion  440  to the highest point of the protruding portion  430 . If the height B is less than 0.3 mm, a gap between the gasket  400  and the cap assembly  300  may be generated during a crimping process, making it difficult to maintain a predetermined compressive pressure. If the height B is greater than 0.6 mm, the protruding portion  430  may be positioned higher and the cap assembly  300  disposed on the protruding portion  430  may be positioned higher accordingly. Thus, an excessive compressive force may be applied to the gasket  400  during a crimping process, resulting in interference between current interrupt device (CID) components. 
         [0057]    The tilt angle θ formed between the protruding portion  430  and the bottom portion  420  may be in a range from 25° to 75°. If the tilt angle θ is less than 25°, the gasket  400  may be insufficiently compressed, resulting in a reduction of the compressive pressure. By contrast, if the tilt angle θ is greater than 75°, the gasket  400  may be excessively deformed, which is undesirable. 
         [0058]    Next, a secondary battery according to another embodiment will be described. 
         [0059]      FIG. 4  is a frontal section view of a gasket of a secondary battery according to the illustrated embodiment. 
         [0060]    Referring to  FIG. 4 , a gasket  400   a  of the secondary battery includes a sidewall portion  410 , a bottom portion  420 , a protruding portion  430 , a concave portion  440  formed between the protruding portion  430  and an inner surface  411  of the sidewall portion  410 , and a reinforcement member  450  formed between the protruding portion  430  and the inner surface  411  of the sidewall portion  410  and contacting the inner surface  411  of the sidewall portion  410  and the bottom surface of the concave portion  420 . 
         [0061]    The secondary battery according to the illustrated embodiment is substantially the same as that according to the previous embodiment as shown in  FIGS. 1 through 3C  in view of configuration and function, except that the reinforcement member  450  is further provided. Thus, explanations of common features will not be repeated, and the following description will focus on only the reinforcement member  450 . 
         [0062]    The reinforcement member  450  is formed between the protruding portion  430  and the inner surface  411  of the sidewall portion  410 . Specifically, the reinforcement member  450  may be formed at a predetermined position of the bottom surface of the concave portion  440 , thereby further increasing the compressive pressure. The reinforcement member  450  may be formed to contact the inner surface  411  of the sidewall portion  410  and the bottom surface of the concave portion  440 . The reinforcement member  450  may reinforce a relatively weak portion, such as the position on which a force is concentrated during the crimping operation, such as a position where the concave portion  440  and the inner surface  411  of the sidewall portion  410  contact each other, thereby minimizing the gap between the gasket  400   a  and the cap assembly  300 . The reinforcement member  450  may have various shapes. For example, the reinforcement member  450  may be formed to have a top portion having a planar shape. This is for the purpose of increasing the compressive pressure improving effect by increasing a contact area between the protruding portion  450  and the lower sidewall of the safety vent  320  during the crimping operation. 
         [0063]    A height C of the reinforcement member  450  may be in a range of approximately ⅓ to approximately ⅔ of a height B of the protruding portion  430 . If the height C of the reinforcement member  450  is greater than ⅔ of the height B of the protruding portion  430 , the gasket  400   a  may be excessively deformed, which is undesirable. However, if the height C of the reinforcement member  450  is less than ⅓ of the height B of the protruding portion  430 , the effect of reinforcing the relatively weak portion may not be noticeable, so that the compressive pressure increasing effect may not be sufficient. 
         [0064]    Next, a secondary battery according to still another embodiment will be described. 
         [0065]      FIG. 5  is a frontal section view of a gasket of a secondary battery according to still another embodiment. 
         [0066]    Referring to  FIG. 5 , a gasket  400   b  of the secondary battery according to the illustrated embodiment includes a sidewall portion  410 , a bottom portion  420 , a protruding portion  430  having a planar portion  460  formed on top of the same, a concave portion  440  formed between the protruding portion  430  and an inner surface of the sidewall portion  410 , and a reinforcement member  450  positioned between the protruding portion  430  and the inner surface of the sidewall portion  410 . 
         [0067]    The secondary battery according to the illustrated embodiment is substantially the same as that according to the previous embodiment as shown in  FIG. 4  in view of configuration and function, except that the planar portion  460  is formed on top of the protruding portion  430 . Thus, explanations of common will not be repeated and the following description will focus on only the planar portion  460 . 
         [0068]    As stated above, the planar portion  460  is formed on top of the protruding portion  430 . 
         [0069]    The planar portion  460  effectively increases the compressive pressure by sufficiently compressing the bottom surface of the safety vent  320  and the protruding portion  430  by increasing the contact area therebetween. The planar portion  460  may have a length in a range from 0.1 mm to 0.25 mm. Herein, the term “length” with respect to the planar portion  460  may refer to a distance in a radial direction of the planar portion  460 . If the length of the planar portion  460  is less than 0.1 mm, the contact area between the protruding portion  460  and the bottom surface of the safety vent  320  may be too narrow to obtain the compressive pressure increasing effect. However, if the length of the planar portion  460  is greater than 0.25 mm, the gasket  400   b  may be excessively deformed. 
         [0070]    By way of summation and review, embodiments described herein provide a secondary battery in which a reduction in a compressive force between a cap assembly and a can or in which a gap that may be generated therebetween during a crimping operation may be prevented even when a gasket and the cap assembly are insufficiently compressed. In a secondary battery, the electrode assembly is received in the cylindrical can, and then a beading part is formed on an upper portion of the can, to prevent the electrode assembly from moving in the can. In addition, a gasket is provided inside the upper opening of the can, to secure various battery components, and to seal the can. The cap assembly is disposed inside the gasket, to finish the upper opening of the can. Then, the can is crimped at the upper opening, to combine a cap up of the cap assembly with the gasket. 
         [0071]    According to the embodiments, the protruding portion formed in the gasket and the reinforcement member can prevent a reduction in sealability between the cap assembly and the can when a gasket and the cap assembly are insufficiently compressed or when a gap is generated therebetween during a crimping operation. The secondary battery can maintain sealability between the can and the cap assembly by minimizing a gap generated between the cap assembly and a gasket during crimping of the can using a concave portion formed between a protruding part and an inner surface of the gasket. 
         [0072]    Example embodiments have been disclosed herein, and although specific terms are employed, they are used and are to be interpreted in a generic and descriptive sense only and not for purpose of limitation. In some instances, as would be apparent to one of ordinary skill in the art as of the filing of the present application, features, characteristics, and/or elements described in connection with a particular embodiment may be used singly or in combination with features, characteristics, and/or elements described in connection with other embodiments unless otherwise specifically indicated. Accordingly, it will be understood by those of skill in the art that various changes in form and details may be made without departing from the spirit and scope thereof as set forth in the following claims.