Abstract:
A battery cap assembly, including a first cap part and a safety apparatus provided under the first cap part, wherein the first cap part includes protrusions on a lower surface thereof, the protrusions configured to engage the safety apparatus.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The present invention relates to a battery cap assembly. More particularly, the present invention relates to a battery cap assembly having an upper cap part, a safety apparatus and protrusions on a lower surface of the upper cap part to engage the safety apparatus, as well as a battery having the same and a method of making the same. 
         [0003]    2. Description of the Related Art 
         [0004]    Batteries are manufactured in a wide variety of forms and may employ any of a number of electrochemical technologies. Batteries may be generally classified as single-use, or primary, batteries and rechargeable, or secondary, batteries. Recently, rechargeable battery technology has been rapidly developed, and the advantages of rechargeability, low weight, and large capacity have led to increasing use of rechargeable batteries such as Ni-MH and Li-ion batteries. 
         [0005]    Battery forms may include, e.g., can type and pouch type batteries used for lithium rechargeable batteries, with the type being classified based on the shape of the container that houses the electrode assembly. Can type batteries may be classified into polygon, or prismatic, type rechargeable batteries and cylindrical type rechargeable batteries. The polygon type rechargeable battery may be formed by molding a thin container into a rectangular parallelepiped shape, or a shape in which edges of the side walls of the rectangular parallelepiped are curved. The cylindrical type rechargeable battery is widely used for electronic and electrical devices that require large capacity, often with multiple batteries coupled to each other to form a battery pack. 
         [0006]    Advances in battery development have let to the inclusion of multiple components in some batteries, e.g., the inclusion of safety devices within the battery container. However, these developments also add complexity to the batteries, which increases the likelihood of reliability issues and battery failure. 
       SUMMARY OF THE INVENTION 
       [0007]    The present invention is therefore directed to a cap assembly, a battery having the same, and method of making the same, which substantially overcome one or more of the problems due to the limitations and disadvantages of the related art. 
         [0008]    It is therefore a feature of an embodiment of the present invention to provide a cap assembly for a battery in which an upper part of the cap assembly is configured to be firmly connected to an underlying part, which may prevent an increase in contact resistance between the parts. 
         [0009]    It is therefore another feature of an embodiment of the present invention to provide a cap assembly for a battery in which an upper part of the cap assembly has at least one protrusion on a lower surface thereof to engage an underlying safety apparatus. 
         [0010]    At least one of the above and other features and advantages of the present invention may be realized by providing a battery cap assembly including a first cap part, and a safety apparatus provided under the first cap part, wherein the first cap part includes protrusions on a lower surface thereof, the protrusions configured to engage the safety apparatus. 
         [0011]    The protrusions may be media blasted protrusions. The protrusions may be arranged in a predetermined pattern, and the protrusions may be a mold of the first cap part. A hardness of the protrusions may be greater than a hardness of a facing surface of the safety apparatus. The protrusions may include at least one of plated steel, stainless steel, and nickel. The facing surface of the safety apparatus may include at least one of aluminum and aluminum alloy. The protrusions may have a height of about 5 μm to about 200 μm. 
         [0012]    The first cap part and the safety apparatus may be welded together. 
         [0013]    The safety apparatus may include a safety device that may be configured to be transformed by an internal battery pressure that exceeds a predetermined pressure, the safety device including a central protrusion that projects from a lower surface of the safety device, and a current intercepting unit that may operate by the transformation of the safety device, wherein the protrusions may contact a surface of the safety device. The safety device may be configured to release the internal battery pressure from a lower surface of the safety device to an upper surface of the safety device when the internal battery pressure exceeds the predetermined pressure. 
         [0014]    At least one of the above and other features and advantages of the present invention may also be realized by providing a battery, including a battery housing defining a cavity and having an opening, an electrode assembly disposed within the cavity, and a cap assembly provided in the opening and electrically coupled with an electrode of the electrode assembly, wherein the cap assembly includes a first cap part; and a safety apparatus disposed between the first cap part and the electrode, wherein the first cap part includes protrusions on a lower surface thereof, the protrusions configured to engage the safety apparatus, and the safety apparatus electrically couples the first cap part to the electrode. 
         [0015]    The safety apparatus may include a safety device that may be configured to be transformed by an internal battery pressure that exceeds a predetermined pressure, the safety device including a central protrusion that projects from a lower surface of the safety device, and a current intercepting unit that may operate by the transformation of the safety device, wherein the protrusions may contact a surface of the safety device. The protrusions of the first cap part may have a height of about 5 μm to about 200 μm. A hardness of the protrusions of the first cap part may be greater than a hardness of a facing surface of the safety apparatus. The battery may be a rechargeable battery. 
         [0016]    At least one of the above and other features and advantages of the present invention may further be realized by providing a method of making a battery, including forming a first cap part, the first cap part including protrusions on a lower surface thereof, arranging the first cap part adjacent to a safety apparatus, disposing the first cap part and the safety apparatus in an opening of a housing of the battery, and deforming an edge of the battery housing adjacent to the opening so as to retain the first cap part and the safety apparatus in the opening, wherein the protrusions are configured to engage the safety apparatus. 
         [0017]    Forming the first cap part may include media blasting the lower surface to form the protrusions. Forming the first cap part may include molding the protrusions into the first cap part. The protrusions may be formed of a first material and a surface of the safety apparatus that faces the protrusions may be formed of a second material, the first material being harder than the second material. Deforming the edge of the battery housing may press the protrusions against the safety apparatus. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0018]    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: 
           [0019]      FIG. 1  illustrates a partial sectional view of a cap assembly and battery according to an embodiment of the present invention; 
           [0020]      FIG. 2A  illustrates a plan view of a safety apparatus according to an embodiment of the present invention; 
           [0021]      FIG. 2B  illustrates a bottom perspective view of the safety apparatus of  FIG. 2A ; 
           [0022]      FIG. 2C  illustrates a bottom view of the safety apparatus of  FIG. 2A ; 
           [0023]      FIG. 3A  illustrates sectional and enlarged views of an upper cap part of a cap assembly according to an embodiment of the present invention; 
           [0024]      FIG. 3B  illustrates plan and enlarged views of an upper cap part of a cap assembly according to an embodiment of the present invention; and 
           [0025]      FIGS. 4A-4C  illustrate bottom and perspective views of an upper cap part of a cap assembly according to embodiments of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0026]    Korean Application No. 2005-134561, filed Dec. 29, 2005, in the Korean Intellectual Property Office, and entitled: “Cap Assembly and Rechargeable Battery Employing the Same,” is incorporated by reference herein in its entirety. 
         [0027]    The present invention will now be described more fully hereinafter with reference to the accompanying drawings, in which exemplary embodiments of the invention are illustrated. 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. 
         [0028]    In the figures, the dimensions of layers and regions may be exaggerated for clarity of illustration. It will also be understood that when a layer or element is referred to as being “on” another layer or substrate, it can be directly on the other layer or substrate, or intervening layers may also be present. Further, it will be understood that when a layer is referred to as being “under” another layer, it can be directly under, and one or more intervening layers may also be present. In addition, it will also be understood that when a layer is referred to as being “between” two layers, it can be the only layer between the two layers, or one or more intervening layers may also be present. Like reference numerals refer to like elements throughout. 
         [0029]    Hereinafter, embodiments of the present invention will be described in detail with reference to  FIGS. 1-4C .  FIG. 1  illustrates a partial sectional view of a cap assembly and battery according to an embodiment of the present invention,  FIG. 2A  illustrates a plan view of a safety apparatus according to an embodiment of the present invention,  FIG. 2B  illustrates a bottom perspective view of the safety apparatus of  FIG. 2A , and  FIG. 2C  illustrates a bottom view of the safety apparatus of  FIG. 2A . 
         [0030]    Referring to FIGS.  1  and  2 A- 2 C, a battery according to an embodiment of the present invention may include a cap assembly  20  having an upper cap part  3  and an underlying safety apparatus  9 . The upper cap part  3  may have a plurality of protrusions  25   a  on a lower surface thereof, and the protrusions  25   a  may be configured to engage the safety apparatus  9 , which may improve reliability of the battery without requiring significant changes to the battery structure or the manufacturing process. The cap assembly  20  may be implemented in a rechargeable battery in order to increase the life of the rechargeable battery, e.g., when the battery is used in a high-vibration application such as a power tool. 
         [0031]    The battery may include an electrode assembly  1  having a winding of a positive electrode and a negative electrode with a separator interposed therebetween (details not shown). The electrode assembly  1  may include, e.g., metal foil current collectors that are coated with an active material slurry. 
         [0032]    The electrode assembly  1  may be accommodated in a can  2 , which may be connected to the negative electrode. The cap assembly  20  may be connected to the positive electrode, with the cap assembly  20  and the can  2  insulated from each other by a gasket  4  interposed therebetween. 
         [0033]    An insulating plate  26  may be disposed on the electrode assembly  1  below the cap assembly  20 . The can  2  may have a bead formed therein near an upper edge, the bead configured to retain the cap assembly  20 . An electrolyte may be injected into the can  2 , and the cap assembly  20  may close the can  2 . Upon final assembly, the end of the opening of the can  2  may be sealed, e.g., by crimping or rolling the end of the opening. 
         [0034]    The upper cap part  3  may have at least one protrusion  25   a  formed on the lower surface thereof that engages the safety apparatus  9 . The safety apparatus  9  may be configured to prevent dangerous conditions within the battery in the event of, e.g., overcharge or short circuit conditions, high pressure or high temperature conditions, etc. The safety apparatus  9  may form part of the internal electrical connections of the battery, such that current passes through the safety apparatus  9  to the upper cap part  3 . 
         [0035]    The upper cap part  3  may include one or more holes  10 , which may be provided in order to discharge gases from the battery. Controlled discharge of the gases may be provided by a safety device  5  in the safety apparatus  9 , the safety device  5  being disposed below the upper cap part  3  and electrically connected to the upper cap part  3 . The gasket  4  may seal flanged edges of the safety device  5  to internal sides of the can  2 , providing an air-tight seal during normal operation of the battery. 
         [0036]    The safety device  5  may have a protrusion  8  in the center thereof that projects toward the electrode assembly  1 . The safety apparatus  9  may also include a current intercepting unit  6  that operates by transformation of the safety device  5 . The safety device  5  may be, e.g., a metal plate configured to be transformed if an internal pressure of the battery exceeds a predetermined amount. An insulating plate  11 , e.g., a plastic plate, may be provided below the safety device  5 . 
         [0037]    A disk  23  may be provided below the insulating plate  11 . The disk  23  may have sufficient strength to remain planar and may have a hole  21  formed in a center thereof, the hole  21  disposed and sized to accommodate the protrusion  8  of the safety device  5  such that the protrusion  8  extends through the disk  23 . The disk  23  may also have vent holes  22  therein, in order to expose the safety device  5  to any pressure that develops within the battery. The insulating plate  11  may be interposed between the disk  23  and the safety device  5  and may insulate the disk  23  and the safety device  5  from each other. 
         [0038]    A plate  24 , e.g., a thin metal plate, may cover the hole  21  in the disk  23 . The plate  24  may be welded to the disk  23 . The plate  24  may be electrically connected to a negative electrode tab  7  from the electrode assembly  1 . 
         [0039]    As noted above, the battery may be sealed by a crimping operation. 
         [0040]    Referring to  FIGS. 3A and 3B , when the end of the opening of the can  2  is crimped, the protrusions  25   a  formed on the lower surface of the upper cap part  3  may be pressed against the upper surface of the safety device  5  in order to engage the upper surface. Thus, intimate contact between the upper cap part  3  and the safety device  5  may be achieved. This may help avoid increases in the internal electrical resistance of the battery caused by vibration, etc., that would otherwise disrupt the electrical connection between the upper cap part  3  and the safety device  5 . 
         [0041]    The upper surface of the safety device  5  may be formed of a conductive material and may have a lower hardness that the protrusions  25   a  on the upper cap part  3 , such that the protrusions  25   a  may embed themselves into the upper surface of the safety device  5 . The protrusions  25   a  may likewise be conductive and may be formed of the same material as the remainder of the upper cap part  3 . For example, the safety device  5  may be formed of aluminum metal, and the protrusions  25   a  and the upper cap part  3  may be formed of a harder metal. The upper cap part  3  may be initially formed or subsequently processed so that the protrusions  25   a  project from the lower surface thereof. 
         [0042]    Forming the upper cap part  3  in this manner may help maintain good electrical contact between the upper cap part  3  and the safety device  5  without requiring significant changes to the manufacturing process. Therefore, it may be possible to tightly seal the rechargeable battery, increase the ability of the battery components to tolerate vibration, increase the ability of the battery to withstand internal pressure, and maintain a low contact resistance between the upper part of the cap assembly  3  and the safety device  5 . In particular, it may help prevent the electrical coupling of the cap assembly from deteriorating when the battery is used for an apparatus that continuously vibrates, e.g., an electrically driven tool, thereby avoiding an undue increase in internal resistance of the battery. 
         [0043]    According to an embodiment of the present invention, the protrusions  25   a  on the lower surface of the upper case part  3  may be formed in any suitable shape, so long as the lower surface of the upper cap part  3  engages the safety device  5 , e.g., to be embedded into the upper surface of the safety device  5 , when the lower surface of the upper cap part  3  presses the upper surface of the safety device  5 . The protrusions formed on the lower surface of the upper cap part  3  may have a height of about 5 μm to about 200 μm. In an implementation, the protrusions  25   a  may be sharp, so as to more easily embed into the upper surface of the safety device  5 . 
         [0044]    According to an embodiment of the present invention, protrusions  25   a  formed on the lower surface of the upper cap part  3  may be formed by molding the upper cap part  3 , e.g., using casting, stamping, etc., and then media blasting, e.g., sand blasting, etc., the lower surface of the upper cap part  3 , so as to make the lower surface of the upper cap part  3  rough. For example, after manufacturing the upper cap part  3  using a mold, a media blast process may be performed to form the protrusions  25   a . In the media blast process, particles such as sand grains may be made to collide with the lower surface of the upper cap part  3 , which is thereby processed to make the surface rough. 
         [0045]    According to another embodiment of the present invention, protrusions  25   a  may be formed in the lower surface of the upper cap part  3  directly in the molding process, e.g., by casting, stamping, etc. to shape the upper cap part  3  and the protrusions  25   a  at the same time, in which case it may be possible to more precisely establish the desired shape, size, and number of protrusions  25   a  and to make the shape of the protrusions  25   a  uniform. Thus, as illustrated in  FIGS. 4A-4C , it may be possible to make the protrusions  25   a  have various shapes and/or patterns. Therefore, it may be possible to process the lower surface of the upper cap part  3  to exhibit characteristics that are particularly suitable for the intended application, e.g., a rechargeable battery for use in a power tool. 
         [0046]      FIGS. 4A-4C  are bottom views of upper cap parts  3  according to embodiments of the present invention, alongside partial perspective views illustrating sections taken along the lines A-A, B-B, and C-C, respectively. Various sharp protrusions  25   a ,  25   b , and  25   c  may be obtained by processing the lower surface of the upper cap part  3  as illustrated in  FIGS. 4A-4C . Referring to  FIG. 4A , the protrusions  25   a  may be discrete protrusions formed in a predetermined arrangement, e.g., in radially-arranged rows. Referring to  FIG. 4B , the protrusions  25   b  may be continuous protrusions formed in a predetermined arrangement, e.g., in concentric circles. Referring to  FIG. 4C , the protrusions  25   c  may be discrete protrusions formed in a more or less random pattern. 
         [0047]    According to an embodiment of the present invention, in order to improve the coupling force between the upper cap part  3  and the safety apparatus  9 , the lower surface of the upper cap part  3  and the upper surface of the safety apparatus  9  may also be coupled with each other by welding the lower surface of the upper cap part  3  and the upper surface of the safety apparatus  9  to each other. 
         [0048]    The vibration tolerance of a battery having a structure as described above may be established using a drum test, which is a vibration test that may be performed on a rechargeable battery by putting the battery in a drum and rotating the drum for 30 minutes at a speed of 66 rpm, in order to determine the degree of the increase in the internal resistance of the battery. An internal resistance increase of 10% or more may be associated with a defective rechargeable battery. 
         [0049]    In a battery according to an embodiment of the present invention, it may be possible to prevent the coupling force of the cap assembly from deteriorating when the battery is used for a high vibration application such as an electric tool. Accordingly, it may be possible to prevent the internal resistance of the battery from increasing, and thus prevent significant reductions in the life of the battery. 
         [0050]    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.