Abstract:
A can includes a body receiving an electrode assembly of a battery and a bottom wall protruding downward from the body and having a convex bottom surface such that the bottom wall does not bend toward an inner portion of the can when the body is compressed.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a can and a battery using the same. More particularly, the present invention relates to a can and a battery using the same, in which a bottom wall of the can protrudes downward while forming a convex bottom surface such that the bottom wall of the can is prevented from being bent toward an inner portion of the can when the battery is compressed. 
     2. Description of the Prior Art 
     Recently, portable wireless appliances, such as video cameras, cellular phones and laptop computers, have been fabricated to be light-weight while performing various functions. This proliferation of portable wireless appliances has increased demand for secondary batteries used as power sources for the portable wireless appliances. Such secondary batteries include Ni—Cd batteries, Ni—MH batteries, Ni—Zn batteries and lithium batteries. Of particular interest are lithium secondary batteries, which are rechargeable, compact and have a high capacity. The lithium secondary batteries provide a high operational voltage and high energy density per unit weight, so they are extensively used in the advanced electronic technology fields. 
       FIG. 1  illustrates an exploded perspective view of a conventional lithium secondary battery. The lithium secondary battery includes an electrode assembly  112  having a positive electrode plate  113 , a negative electrode plate  115  and a separator  114  in a can  110 . The electrode assembly  112  is provided together with an electrolyte in the can  110  by sealing an upper opening  110   a  of the can  110  using a cap assembly  120 . 
     In general, the can  110  is made from aluminum or an aluminum alloy through a deep drawing process. A bottom wall  110   b  of the can  110  has a substantially planar shape. 
     The electrode assembly  112  is formed by interposing the separator  114  between the positive and negative plates  113  and  115  and winding them into a jelly-roll structure. A positive electrode tap  116  is attached to the positive electrode plate  113  and protrudes upward out of the electrode assembly  112 . A negative electrode tap  117  is attached to the negative electrode plate  115  and protrudes upward out of the electrode assembly  112 . The positive electrode tap  116  is spaced apart from the negative electrode tap  117  by a predetermined distance such that they are electrically insulated from each other. In general, the positive and negative electrode taps  116  and  117  are made from Ni. 
     The cap assembly  120  includes a cap plate  140 , an insulating plate  150 , a terminal plate  160  and an electrode terminal  130 . The cap assembly  120  is accommodated in an insulating case  170  and attached to the upper opening  110   a  of the can  110 , thereby sealing the can  110 . 
     The cap plate  140  is made from a metal plate having a size and a shape corresponding to those of the upper opening  110   a  of the can  110 . The cap plate  140  includes a first terminal hole  141  having a predetermined size at the center of the cap plate  140 . The electrode terminal  130  is inserted into the first terminal hole  141 . When the electrode terminal  130  is inserted into the first terminal hole  141 , a gasket tube  146  is provided around the electrode terminal  130  in order to insulate the electrode terminal  130  from the cap plate  140 . An electrolyte injection hole  142  is formed at one side of the cap plate  140  with a predetermined size. After the cap assembly  120  has been assembled with the upper opening  110   a  of the can  110 , the electrolyte is injected into the can  110  through the electrolyte injection hole  142 . Then, the electrolyte injection hole  142  is sealed with a separate sealing unit (not shown). 
     The electrode terminal  130  is connected to the negative electrode tap  117  of the negative electrode plate  115  or the positive electrode tap  116  of the positive electrode plate  113  so that the electrode terminal  130  may serve as a negative electrode terminal or a positive electrode terminal. 
     The insulating plate  150  is made from an insulating material identical to the material for the gasket tube  146  and is coupled with the lower surface of the cap plate  140 . The insulating plate  150  is formed with a second terminal hole  151 , which is aligned corresponding to the first terminal hole  141  of the cap plate  140  and into which the electrode terminal  130  is inserted. A resting recess  152  is formed on a lower surface of the insulating plate  150 , and has a size and a shape corresponding to those of the terminal plate  160  such that the terminal plate  160  can fit in the resting recess  152 . 
     The terminal plate  160  is made from a Ni alloy and is coupled with the lower surface of the insulating plate  150 . The terminal plate  160  is formed with a third terminal hole  161 , which is aligned corresponding to the first terminal hole  141  of the cap plate  140  and into which the electrode terminal  130  is inserted. Since the electrode terminal  130  inserted into the first terminal hole  141  of the cap plate  140  is insulated from the terminal plate  140  by the gasket tube  146 , the terminal plate  160  can be electrically connected to the electrode terminal  130  while being electrically insulated from the cap plate  140 . 
     The negative electrode tap  117  attached to the negative electrode plate  115  is welded to one side of the terminal plate  160  and the positive electrode tap  116  attached to the positive electrode plate  113  is welded to the other side of the terminal plate  160 . In order to weld the positive and negative electrode taps  116  and  117  to the terminal plate  160 , a resistance welding process or a laser welding process is performed. Typically, the resistance welding process is used for welding the positive and negative electrode taps  116  and  117  to the terminal plate  160 . 
     As the energy density of the battery increases, the size of the battery is decreased, making it more vulnerable to impact and compression. Thus, if the battery is subject to such impact or compression, the electrode assembly accommodated in the can may be deformed, thereby causing the short circuit between electrode plates and accidental ignition or explosion of the lithium battery. 
     In particular, as shown in  FIG. 1 , when the longitudinal compression test, which is one of safety tests for batteries, is performed by applying a compression force Fa, the battery is deformed about the longitudinal axis (b) thereof. As a result, the bottom wall  110   b  of the can  110  is bent toward the inner portion of the can  110 , thereby locally compressing a lower portion of the electrode assembly, causing a short circuit between electrode plates of the electrode assembly. 
     SUMMARY OF THE INVENTION 
     The present invention is therefore directed to a can for a battery and a battery using the same, which substantially overcomes one or more of the problems due to the limitations and disadvantages of the related art. 
     It is a feature of an embodiment of the present invention to provide a can and a battery using the same, in which a bottom wall of the can protrudes downward while forming a convex bottom surface. 
     It is another feature of an embodiment of the present invention to provide a can and a battery using the same, such that the bottom wall of the can is prevented from being bent toward an inner portion of the can when the battery is compressed in a direction perpendicular to a longitudinal axis thereof, thereby improving safety of the battery. 
     At least one of the above and other features and advantages of the present invention may be realized by providing a can for a battery including an electrode assembly having a positive electrode plate, a negative electrode plate and a separator interposed between the positive and negative electrode plates, the can including a body to receive the electrode assembly and a bottom wall protruding downward from the body and having a convex surface. 
     At least one of the above and other features and advantages of the present invention may be realized by providing a battery including an electrode assembly including a positive electrode plate, a negative electrode plate and a separator interposed between the positive and negative electrode plates, and a can including a body accommodating the electrode assembly therein and a bottom wall, the bottom wall protruding downward from the body and having a convex surface. 
     The body may have an open substantially box-shaped structure including opposing front and rear walls and lateral sidewalls. The bottom wall may be rounded lengthwise along long-lateral sides thereof at a predetermined curvature. The bottom wall may be rounded widthwise along short-lateral sides thereof at a predetermined curvature. The bottom wall may be rounded lengthwise and widthwise along long-lateral sides and short-lateral sides thereof at a predetermined curvature. A vertex of the bottom wall may have a height of at least about 0.1 mm, at least about 50% of a thickness of the bottom wall and/or less than about 2 mm. The bottom wall may include a planar surface having a predetermined size, which may correspond to a size of a lead plate to be welded to the bottom wall of the can. The planar surface may be in a center portion of the bottom wall and may be at a vertex of the bottom wall. The body and the bottom wall are integral. The body and the bottom wall may be of a same material. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above and other features and advantages of the present invention will become more apparent to those of ordinary skill in the art by describing in detail exemplary embodiments thereof with reference to the attached drawings in which: 
         FIG. 1  illustrates an exploded perspective view of a conventional lithium secondary battery; 
         FIG. 2A  illustrates a perspective view of a can for a lithium secondary battery according to a first embodiment of the present invention; 
         FIG. 2B  illustrates a sectional view taken along line A-A shown in  FIG. 2A ; 
         FIG. 3A  illustrates is a perspective view of a can for a lithium secondary battery according to a second embodiment of the present invention; 
         FIG. 3B  illustrates a sectional view taken along line B-B shown in  FIG. 3A ; 
         FIG. 4  illustrates a perspective view illustrating a can for a lithium secondary battery according to a third embodiment of the present invention; 
         FIG. 5A  illustrates a perspective view illustrating a can for a lithium secondary battery according to a fourth embodiment of the present invention; and 
         FIG. 5B  illustrates a sectional view taken along line C-C shown in  FIG. 5A . 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Korean Patent Application No. 2004-0098860, filed on Nov. 29, 2004, in the Korean Intellectual Property Office, and entitled: “Can for Lithium Secondary Battery and Lithium Secondary Battery Using the Same,” is incorporated by reference herein in its entirety. 
     The present invention will now be described more fully hereinafter with reference to the accompanying drawings, in which exemplary embodiments of the invention are shown. The invention may, however, 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. In the figures, the dimensions of layers and regions are exaggerated for clarity of illustration. Like reference numerals refer to like elements throughout. 
       FIG. 2A  illustrates a perspective view of a can  200  for a battery according to a first embodiment of the present invention.  FIG. 2B  is a sectional view taken along line A-A shown in  FIG. 2A . 
     Referring to  FIGS. 2A and 2B , the can  200  according to the first embodiment of the present invention has front and rear walls  210 , lateral sidewalls  220  and a bottom wall  230 . The can  200  may be made of metal, preferably a lightweight and flexible metal, e.g., aluminum or an aluminum alloy. However, the materials for the can  200  are not so limited. 
     The front and rear walls  210  may be integrally formed with the lateral sidewalls  220  and the bottom wall  230 , e.g., using a deep drawing process. The front and rear walls  210  of the can  200  are opposite to and spaced apart from each other, thereby forming front and rear surfaces of the can  200 . The lateral sidewalls  220  of the can  200  are opposite to and spaced apart from each other, thereby forming left and right lateral surfaces of the can  200 . 
     Although the lateral sidewalls  220  of the can  200  are shown as having planar surfaces, the lateral sidewalls  220  of the can  200  may have convex surfaces. That is, if the lateral surfaces of an electrode assembly accommodated in the can  200  have convex surfaces, the lateral sidewalls  220  of the can  200  may also have convex surfaces corresponding to the lateral surfaces of the electrode assembly. Similarly, while the body of the can  200  formed by the front and rear walls  210  and the lateral sidewalls  220  is shown is having an open substantially box-shaped structure may be any shape convenient for surrounding the electrode assembly. 
     The bottom wall  230  forms a bottom surface of the can  200 . The bottom wall  230  of the can  200  may protrude downward from the body, i.e., from the front and rear walls  210  and the lateral sidewalls  220 , and may have a convex surface. In detail, the bottom wall  230  may be rounded lengthwise along long-lateral sides  210   a  thereof (which may also serve as lower sides of the front and rear walls  210  of the can  200 ) in a predetermined curvature. That is, the bottom wall  230  of the can  200  may gradually protrude downward from both short-lateral sides  220   a  thereof along the long-lateral sides  210   a , thereby forming the convex bottom surface of the can  200 . The bottom wall  230  of the can  200  may not be rounded widthwise along the short-lateral sides  220   a  thereof. Accordingly, the bottom wall  230  together with the front and rear walls  210  of the can  200  form a U-shaped structure, as can be seen in  FIG. 2B . 
     The bottom wall  230  may protrude downward by a height of at least about 0.1 mm. The convex bottom surface may be a curved surface having a maximum height corresponding to at least about 50% of the thickness of the bottom wall  230 . That is, a longitudinal distance between a first virtual horizontal plane at a bottom of the body, i.e., a boundary plane between the body and the bottom wall  230 , and a second virtual horizontal plane at a vertex of the convex bottom surface, i.e., a plane tangential to the vertex, may be equal to or greater than about 50% of a thickness of the bottom wall  230 . If the height of the convex bottom surface is too small, the convex bottom surface has a small curvature, so that the bottom wall  230  of the can  200  may not be effectively bent outward when the can  200  is subject to longitudinal compression. In contrast, if the height of the convex bottom surface is too large, the size of the battery increases without increasing its capacity. Accordingly, the height of the convex bottom surface of the bottom wall  230  must be properly determined according to the type and capacity of the battery. The height of the convex bottom surface of the bottom wall  230  may be less than about 2 mm. 
       FIG. 3A  illustrates a perspective view of a can  300  for a battery according to a second embodiment of the present invention.  FIG. 3B  illustrates a sectional view taken along line B-B shown in  FIG. 3A . 
     Referring to  FIGS. 3A and 3B , the can  300  according to the second embodiment of the present invention includes a bottom wall  330  protruding downward while forming a convex bottom surface. In detail, the bottom wall  330  may be rounded widthwise along short-lateral sides  320   a  thereof (which may also serve as lower sides of lateral sidewalls  320  of the can  300 ) in a predetermined curvature. That is, the bottom wall  330  of the can  300  may gradually protrude downward from both long-lateral sides  310   a  thereof along the short-lateral sides  320   a , thereby forming the convex bottom surface of the can  300 . The bottom wall  330  of the can  300  may not be rounded lengthwise along the long-lateral sides  310   a  thereof. Accordingly, the bottom wall  330  together with the lateral sidewalls  320  forms a U-shaped structure, as shown in  FIG. 3B . 
     The bottom wall  330  may protrude downward by a height of at least about 0.1 mm. The convex bottom surface may be a curved surface having a maximum height corresponding to at least about 50% of the thickness of the bottom wall  330 . That is, a longitudinal distance between a first virtual horizontal plane at a bottom of the body and a second virtual horizontal plane at a vertex of the convex bottom surface may be equal to or greater than about 50% of a thickness of the bottom wall  330 . If the height of the convex bottom surface is too small, the convex bottom surface has a small curvature, so that the bottom wall  330  of the can  300  may not be effectively bent outward when the can  300  is subject to longitudinal compression. In contrast, if the height of the convex bottom surface is too large, the size of the battery increases without increasing its capacity. Accordingly, the height of the convex bottom surface of the bottom wall  330  must be properly determined according to the type and capacity of the battery. The height of the convex bottom surface of the bottom wall  330  may be less than about 2 mm. 
       FIG. 4  illustrates a perspective view of a can  400  for a battery according to still a third embodiment of the present invention. 
     Referring to  FIG. 4 , the can  400  according to the third embodiment of the present invention includes a bottom wall  430  protruding downward while forming a convex bottom surface. In detail, the bottom wall  430  of the can  400  may be rounded both lengthwise and widthwise along long-lateral sides  410   a  and short-lateral sides  420   a  thereof (which may also serve as lower sides of front and rear walls  410  and lower sides of lateral sidewalls  420 , respectively) in a predetermined curvature. That is, the bottom wall  430  may gradually protrude downward from both long-lateral sides  410   a  and short-lateral sides  420   a  thereof, thereby forming the convex bottom surface of the can  400 . Thus, the bottom wall  430  has a substantially spherical structure. 
     The bottom wall  430  may protrude downward by a height of at least about 0.1 mm. The convex bottom surface may be a curved surface having a maximum height corresponding to at least about 50% of the thickness of the bottom wall  430 . That is, a longitudinal distance between a first virtual horizontal plane at a bottom of the body and a second virtual horizontal plane at a vertex of the convex bottom surface may be equal to or greater than about 50% of a thickness of the bottom wall  430 . If the height of the convex bottom surface is too small, the convex bottom surface has a small curvature, so that the bottom wall  430  of the can  400  may not be effectively bent outward when the can  400  is subject to longitudinal compression. In contrast, if the height of the convex bottom surface is too large, the size of the battery increases without increasing its capacity. Accordingly, the height of the convex bottom surface of the bottom wall  430  must be properly determined according to the type and capacity of the battery. The height of the convex bottom surface of the bottom wall  430  may be less than about 2 mm. 
       FIG. 5A  illustrates a perspective view of a can  500  for a battery according to a fourth embodiment of the present invention.  FIG. 5B  illustrates a sectional view taken along line C-C shown in  FIG. 5A . 
     Referring to  FIGS. 5A and 5B , the can  500  according to the fourth embodiment of the present invention includes a bottom wall  530  protruding downward while forming a convex bottom surface of the can  500 , in which a planar surface  535  having a predetermined size is formed at the center of the convex bottom surface of the can  500 . In detail, the bottom wall  530  of the can  500  is rounded lengthwise along long-lateral sides  510   a  thereof (which may also serve as lower sides of front and rear walls  510 ) while forming the planar surface  535  at the center thereof. Preferably, the size of the planar surface  535  corresponds to the size of a lead plate (not shown) to be attached to the bottom wall  530  of the can  500 . The lead plate connected to a secondary protective device (not shown) can be welded to the bottom wall  530  of the can  500  according to the type of the lithium secondary battery. Welding is facilitated if a welding section of the bottom wall  530  for the lead plate is planar. Thus, the center portion of the bottom wall  530  making contact with the lead plate is provided with the planar surface  535 . 
     A height of the bottom wall  530 , i.e., the height between a root of the bottom wall  530  and the planar surface  535  of the bottom wall  530  may be at least about 0.1 mm. The height of the bottom wall  530  may correspond to at least about 50% of the thickness of the bottom wall  530 . If the height of the bottom wall  530  is too small, the bottom wall  530  may not be effectively bent outward when the can  500  is subject to longitudinal compression. In contrast, if the height of the bottom wall  530  is too large, the size of the battery increases without increasing capacity thereof. Accordingly, the height of the bottom wall  530  must be properly determined according to the type and capacity of the battery. The height of the bottom wall  530  may be less than about 2 mm. 
     Although it is illustrated in  FIGS. 5A and 5B  that the can  500  has the planar surface  535  at the center of the bottom wall rounded lengthwise along the long-lateral sides thereof, the planar surface can be formed on the center of the bottom wall rounded widthwise along the short-lateral sides thereof as shown in  FIGS. 3A and 3B  or on the center of the bottom wall rounded lengthwise and widthwise along the long-lateral sides and short-lateral sides as shown in  FIG. 4 . 
     Hereinafter, an operation of the can for the battery according to the present invention will be described. While the first embodiment is discussed for illustration, the same principles apply to any of the embodiments or variations thereof. 
     Referring to  FIGS. 2A and 2B , when the can  200 , or the battery having the can  200 , is bent about the longitudinal axis thereof due to a compression force Fa applied thereto, the bottom wall  230  of the can  200  is bent outward, i.e., downward, rather than inward. Since the bottom wall  230  bends outward, compression is not applied to the lower portion of the electrode assembly (not shown) in the can  200 , thus preventing a short circuit between the electrode plates of the electrode assembly and improving safety of the battery. 
     Although the present invention has been described in relation to the lithium secondary battery, the can of the present invention is also applicable for other batteries. 
     As described above, according to embodiments of a can for a battery of the present invention, the bottom wall of the can protrudes downward while forming the convex bottom surface in such a manner that the bottom wall of the can is bent outward from the body of the can when the lithium secondary battery is deformed due to compression pressure applied thereto. Thus, external impact is prevented from being applied to the lower portion of the electrode assembly accommodated in the can so that a short circuit is not generated between the electrode plates of the electrode assembly. 
     Exemplary embodiments of the present invention 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. Accordingly, it will be understood by those of ordinary skill in the art that various changes in form and details may be made without departing from the spirit and scope of the present invention as set forth in the following claims.