Abstract:
A lithium ion secondary battery in which at least one step portion is formed on an upper surface of a cap plate, and at least one step portion is formed on a lower or first surface of a battery part opposite to the upper or first surface of the cap plate so that the at least two step portions are complementary. The complementary step portions of the cap plate of the bare cell and the battery part provided at an upper part of the cap plate result in easy coupling of the battery part to the bare cell and stable maintenance of the coupling between the battery part and the bare cell. The coupling structure results in greater ease in performing subsequent manufacturing processes and protects the bare cells coupled to the battery part from dislodging.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims priority to and the benefit of Korean Application No. 2006-19431, filed Feb. 28, 2006, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein by reference. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     Aspects of the present invention relate to a lithium ion secondary battery, and more particularly, to a lithium ion secondary battery in which a separate battery part is coupled to an upper or first part of a cap plate of a bare cell. 
     2. Description of the Related Art 
     In general, primary batteries are not rechargeable, and secondary batteries are rechargeable. In recent years, for example, nickel-metal hydride (Ni-MH) batteries, lithium (Li) batteries, and lithium ion (Li-ion) batteries have been mainly used as the secondary batteries. 
     The lithium ion batteries are manufactured in various shapes. For example, the shapes of the lithium ion batteries may be classified into cylindrical, square prismatic, or pouch shapes according to the type of case used in manufacturing. 
     In the lithium ion battery, a carbon-based electrode is generally used as a cathode in order to reduce the risk of combustion or explosion. However, special emphasis is placed on the safety of the lithium ion battery in the manufacturing process due to the high energy density of lithium and the possibility of combustion reactions occurring with a non-aqueous electrolyte. 
     In order to improve the safety, the lithium ion battery generally includes a bare cell having a basic structure for charge or discharge and a protective circuit or a protective device for preventing overcharge, overdischarge, overheating, and overcurrent. The protective circuit or the protective device may be physically and electrically connected to the bare cell in the form of a printed circuit board and may be displaced on the side, the upper surface, or the lower surface of the bare cell. 
     In the cylindrical can battery, a cap assembly of a bare cell serves to prevent overheating and overcurrent. However, in the prismatic can battery, a cap assembly does not have such a safety feature. Therefore, in the prismatic can battery, particularly, a separate safety device should be coupled to the bare cell. In recent years, in many cases, the safety device of the prismatic can battery, such as a protective circuit board, is coupled to the upper surface of a cap plate. 
     Meanwhile, in a pack battery having a plurality of bare cells connected to one another, a battery part, such as a cap cover, may be coupled to an upper part of a cap plate in order for series/parallel connection of the bare cells in the pack or connection between the bare cells and a protective circuit. 
     An example of the cap cover will be described below. A peripheral portion or a body of the cap cover is generally formed of an insulating resin material, and forms a coupling part that is supported by a cap assembly of a bare cell while physically contacting the bare cell. A metal plate terminal that has a relatively narrow width and is connected to an electrode terminal of the bare cell is formed at the center of the lower surface of the cap cover. The narrow metal plate terminal is exposed through a hole formed in the center of the body of the cap cover. A wide metal plate terminal connected to a protective circuit terminal outside the bare cell may be provided in the vicinity of the hole on the upper surface of the cap cover. In addition, a conductive connecting part for connecting these metal plate terminals is provided. 
     However, in the cap assembly at the upper part of the bare cell, an electrode terminal protrudes from the surface of the cap plate and is insulated therefrom. Therefore, it is difficult to stably couple a battery part, such as a cap cover, to an upper part of the cap assembly. Further, it is difficult to stably couple the battery part to the bare cell by, for example, welding. 
     As a member for guiding the battery part to an accurate position with respect to the cell is not formed in the peripheral portion of the cap assembly, it is difficult to accurately couple the battery part to the upper part of the cap assembly. When the battery part is not accurately coupled to the cap assembly, it is difficult to achieve stable electrical connection between the battery part and the bare cell, which may cause defects in the electrical connection. 
     For example, when the cap cover is used for a pack battery, the cap cover should be fixed to the upper part of the cap plate. However, it is difficult to easily fix the cap cover to the cap plate, which may frustrate the manufacture of the pack battery. 
     SUMMARY OF THE INVENTION 
     Accordingly, aspects of the present invention have been contrived to solve the above-described drawbacks, and aspects of the present invention provide a lithium ion secondary battery having a structure capable of stably placing a battery part, such as a cap cover or a protective circuit assembly, on an upper part of a cap assembly. 
     According to an aspect of the invention, a lithium ion secondary battery includes: a bare cell including an electrode assembly having a first electrode, a second electrode, and a separator interposed between the first electrode and the second electrode, a can housing the electrode assembly, and a cap assembly that includes a cap plate coupled to an upper open part of the can and an electrode terminal formed in a through hole of the cap plate so as to be insulated from the through hole; and a battery part coupled to an upper part of the cap assembly of the bare cell. In the lithium ion secondary battery, step portions or step structures are formed on the battery part and the cap plate so as to correspond to each other. 
     According to another aspect of the invention, a lithium ion secondary battery includes: an electrode assembly having a first electrode, a second electrode, and a separator interposed between the first electrode and the second electrode; a can housing the electrode assembly; and a cap assembly that includes a cap plate coupled to an upper open part of the can and an electrode terminal formed in a through hole of the cap plate so as to be insulated from the through hole. In the lithium ion secondary battery, a step portion is formed on the upper surface of the cap plate. 
     Additional aspects and/or advantages of the invention will be set forth in part in the description which follows and, in part, will be obvious from the description, or may be learned by practice of the invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       These and/or other aspects and advantages of the invention will become apparent and more readily appreciated from the following description of the embodiments, taken in conjunction with the accompanying drawings of which: 
         FIG. 1  is a cross-sectional view illustrating a cap cover, serving as a battery part, coupled to an upper part of a cap assembly of a square-shaped bare cell; 
         FIG. 2A  is a plan view illustrating a cap plate according to another embodiment of the invention; 
         FIG. 2B  is a cross-sectional view illustrating the cap plate of  FIG. 2A ; 
         FIG. 3  is a perspective view schematically illustrating the coupling between a protective circuit assembly and a bare cell according to another embodiment of the invention; 
         FIG. 4A  is a plan view illustrating a cap plate according to another embodiment of the invention; 
         FIG. 4B  is a cross-sectional view illustrating the cap plate of  FIG. 4A ; 
         FIG. 5  is a plan view illustrating a cap plate according to another embodiment of the invention; 
         FIG. 6  is a plan view illustrating a cap plate according to another embodiment of the invention; and 
         FIG. 7  is a plan view illustrating a cap plate according to another embodiment of the invention. 
     
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
     Reference will now be made in detail to the present embodiments of the present invention, examples of which are illustrated in the accompanying drawings, wherein like reference numerals refer to the like elements throughout. The embodiments are described below in order to explain the present invention by referring to the figures. 
       FIG. 1  is a partial cross-sectional view illustrating a square-shaped bare cell coupled to a cap cover according to aspects of the invention. Specifically,  FIG. 1  is a cross-sectional view illustrating a necessary portion of the square-shaped bare cell coupled to the cap cover. 
     As shown in  FIG. 1 , the square-shaped bare cell, which comprises at least a cap plate  110  and a can  100 , and the cap cover  440  coupled to each other may be provided in a battery pack in the same manner as cylindrical bare cells are connected in series/parallel to one another in a general battery pack and are connected to a protective circuit module. 
     The connection between the square-shaped bare cell and the cap cover  440  will be described in detail below with reference to  FIG. 1 . As shown in  FIG. 1 , a cap cover  440 , also referred to as a battery part, is generally formed of a resin mold shape by insert injection molding and includes lead plates as electrical terminals formed of nickel. 
     The battery part may be a protective circuit board or the cap cover  440  coupled to a plurality of prismatic can batteries to form a pack battery. In this case, the cap cover  440  can be considered as a connecting part for electrical connection. However, generally, the cap cover  440  may serve as a safety device having a protective element, such as a PTC element  446 , provided therein. The cap cover  440  may be formed in various shapes according to the type of connection among batteries. 
     The lead plates include a first lead plate  444  and a second lead plate  442 . The first lead plate  444  is directly connected to a cathode terminal  120  of the square-shaped bare cell, which is provided at the center of the bare cell. And, a second lead plate  442  provided on the outer surface of the cap cover  440 . After the cap cover  440  is formed, the first lead plate  444  is welded to one terminal of a positive temperature coefficient (PTC) element  446 . And, the other terminal of the PTC element  446  is welded to one end of a connecting plate  447 . The connecting plate  447  electrically connects the PCT element  446  to the second lead plate  442  on the outer surface of the cap cover  440  via a through hole  448 . Thus, the second lead plate  442  is electrically connected to the cathode terminal  120  via the connecting plate  447 , the PTC element  446 , and the first lead plate  444 . 
     The cap cover  440 , or battery part, is placed over a cap plate  110  of the square-shaped bare cell. The PTC element  446  is coupled to the internal surface of the cap cover  440 . In this case, a peripheral rib  4410  extending from a peripheral portion of a plate body  441  of the cap cover  440  toward the cap plate  110  is aligned with the side wall of a can  100 . 
     A U-shaped position fixing rib  4413  and a complementary position fixing groove  320  are provided and collectively referred to as step portions. A step portion will generally have a rib or groove shape and have a corresponding groove or rib shape with which to couple. An end of a U-shaped position fixing rib  4413  is inserted into a position fixing groove  320  formed in the upper or first surface of the cap plate  440 . The U-shaped position fixing rib  4413  may be formed closer to the cathode terminal  120  than to the peripheral rib  4410 . In  FIG. 1 , a first portion  4411  is a cross section of a wall when the U-shaped position fixing rib  4413  is symmetrically cut in the vertical direction. And, a second portion  4412  is a side wall portion of the position fixing rib  4413  and is connected to the cross section of the wall. 
     In this way, the cap cover  440  is fixed relative to the cap plate  110 , and the connection between the cap cover  440  and the cap plate  110  is kept in a stable state. However, other configurations are possible, such as having a protrusion formed in the cap plate  110  that extends to insert into a groove formed in the cap cover  440 . 
     The first lead plate  444  formed on the inner surface of the cap cover  440  is welded to the cathode terminal  120 . Here, a welding rod may be inserted through a hole  445  formed in the center of the cap cover  440 . 
     When the welding is completed, a plurality of square-shaped bare cells coupled to the cap cover  440  are thereby connected in series or parallel to one another in a battery pack and connected to the cap cover  440 , which is a protective circuit module, through separate connecting conductors. The connection of a plurality of bare cells forms a pack-type battery. 
     The complementary corresponding step portions of the cap cover  440  and the cap plate  110  can be easily connected to each other, which makes it possible to easily perform a process of physically coupling the cap cover  440  to the bare cell and to easily progress a subsequent process, such as a welding process. In addition, the complementary corresponding step portions, the fixing rib  4413  and the groove  320 , make it possible to stabilize the connection between the bare cell and the cap cover  440  in the battery pack. As such, a plurality of bare cells may be stably contained in a battery pack. 
     As illustrated, a groove  320  is formed in the upper or first surface of the cap plate  110 , and a protruding step portion, such as the rib  4413 , is formed on the lower or first surface of the plate body  441  of the cap cover  440 . However, a protrusion may be formed on the upper or first surface of the cap plate  110 , and a groove may be formed in the plate body  441  of the cap cover  440 . 
     For example, when the groove  320  is formed in the upper or first surface of the cap plate  110 , a protruding portion, the fixing rib  4413 , that is inserted into the groove  320  is formed on the lower or first surface of the battery part, or the cap cover  440 . Or oppositely, when a fixing rib is formed at the center of the cap plate, a groove is formed on the lower or first surface of the battery part so as to correspond to and accept the fixing rib of the cap plate when the battery part and the cap plate are coupled. The battery part is kept at a fixed position with regard to the bare cell without being detached from the bare cell even when an external force is applied to the battery part or the bare cells. Furthermore, the cap cover  440  and the cap plate  110  need not only include grooves or ribs, but may contain a combination of both grooves and ribs. 
     The fixing rib  4413  may be formed in the lower or first surface of the cap cover  440 , but the shape of the step portions is not limited thereto. That is, the position and size of the step portions may vary according to the type of battery part coupled to the cap plate  110 . The height of the fixing rib  4413  or depth of the groove  320  may range from 10% to 50% of the thickness of the cap plate  110 . For example, when the thickness of the cap plate is about 0.8 mm, the height of the fixing rib  4413  and the depth of the groove  320  may be in the range of 0.1 to 0.4 mm. When the height of the fixing rib  4413  or the depth of the groove  320  is small, it is difficult for the fixing rib  4413  to maintain connection with the groove  320 . On the other hand, when the height of the fixing rib  4413  or depth of the groove  320  is large, it is difficult to form the fixing rib  4413 . Also, the larger the depth of the groove  320 , the smaller the thickness of a portion of the cap plate  110  corresponding to the groove  320  becomes, which may cause damage to or deform the cap plate  110 . 
     In a process of forming the cap plate  110 , the step portions, be they grooves or protrusions, may be formed, for example, by injection molding, pressing, casting, or die casting. A protrusion having a small height may be formed on only the upper or first surface of the cap plate  110  by pressing. In addition, the step portions may be formed on the upper, or first, and lower, or second, surface of the cap plate  110  in a complementary structure. For example, a protrusion may be formed on the upper or first surface of the cap plate  110  and a groove may be formed in the lower or second surface of the cap plate  110  as illustrated in  FIG. 2B . As a result, the sectional structure of the step portions may be conformal. 
     When casting is used, a protrusion may be formed in a rib shape on only the upper or first surface of the cap plate  110 , and the lower or second surface of the cap plate  110  may be formed flat. A step portion having a rib shape may be adhered or welded to the upper or first surface of the cap plate  110 . As the height or depth of the step portions becomes larger and the edges of the step portions are vertically formed without being chamfered, the risk of the battery part, here—the cap cover  440 , being detached from the cap plate  110  is reduced. 
       FIG. 2A  is a plan view illustrating a cap plate according to aspects of the invention, and  FIG. 2B  is a cross-sectional view illustrating a cross section A-A′ of the cap plate of  FIG. 2A .  FIG. 3  is a perspective view illustrating the coupling between a protective circuit assembly and a bare cell according to another aspect of the invention. 
     Referring to  FIG. 2A , a cap plate  110  has a fixing rib  330  formed thereon and the fixing rib  330  is formed in a “U” shape on the outer surface of the cap plate  110 . The fixing rib  330  corresponds to the U-shaped fixing rib  4413  of  FIG. 1  but is formed on the cap plate  110 . The fixing rib  330  extends to insert into a groove of the cap cover (not shown) so as to stabilize the coupling of the bare cell to the cap cover. The electrolyte injection hole  160 , the vent  190 , and a cathode through-hole  111  are formed to extend through the cap plate  110 . During the assembly of the bare cells, electrolyte is injected through the electrolyte injection hole  160 . Also, the cathode through-hole  111  allows the cathode terminal  120  to extend through the cap plate  110 . Referring to  FIG. 2B , the fixing rib  330  is formed by pressing. The electrolyte injection hole  160 , the vent  190 , and the cathode through hole  111  extend through the cap plate  110 . The fixing rib  330  extends from and is an elevated portion above the outer surface of the cap plate  110 . The fixing rib  330  and the corresponding groove formed in a battery part (not shown) are step portions. 
     Referring to  FIG. 3 , a U-shaped groove  537  is formed on the lower or first surface of a protective circuit assembly  530 , which serves as a battery part. The U-shaped groove  537  is formed to correspond to a U-shaped fixing rib  515  formed on a cap plate  520 . The U-shaped groove  537  is formed to accept the insertion of the U-shaped fixing rib  515  formed on the outer surface of the cap plate  520 . As such, the U-shaped fixing rib  515  is formed to a size slightly smaller than that of the U-shaped groove  537 , and the U-shaped fixing rib  515  is inwardly inserted to the U-shaped groove  537 . In this case, the fixing rib  515  enables a battery part, such as the protective circuit assembly  530 , to be stably coupled to the cap plate  520 . The fixing rib  515  serves to prevent the battery part from deviating from a fixed position on the protective circuit assembly  530  due to external forces. The height to which the fixing rib  515  extends above the outer surface of the cap plate  520  and the depth to which the groove  537  is formed in the plate body  531  provide a predetermined space between the plate body  531  and the cap plate  520 . The protective circuit assembly  530  may be formed of molded plastic and be formed to include an external connection electrode  533 . In the protective circuit assembly  530 , an anode terminal may be formed of the U-shaped fixing rib  515  and groove  537 . An edge skirt  535 , formed of plastic, protrudes downward from the lower or first surface of a plate body  531 , also formed of a plastic resin, to surround the protective circuit assembly  530 . The edge skirt  535  may be formed of or coated with a conductive material to be included as an element of the anode terminal. 
     The depth to which a cathode terminal acceptor  539  of the protective circuit assembly  530  extends, and the extent to which a cathode terminal  513  extends above the cap plate  520  of the bare cell  510  may be determined by considering the height of the U-shaped fixing rib  515 , the depth of the U-shaped groove  537 , and the length of the edge skirt  535 . For example, the cathode terminal acceptor  539  may be formed at the center of the lower or first surface of the plate body  531  of the protective circuit assembly  530 , and the height of the anode terminal composed of the U-shaped groove  537 , the U-shaped fixing rib  515  of the cap plate  520 , and the edge skirt  535  may be equal to the height to which the cathode terminal  513  extends above the cap plate  520 . The polarities of the anode terminal and the cathode terminal  513  may be switched. 
     The cathode terminal  513  of the bare cell, the cathode terminal acceptor  539 , contact portions of the U-shaped groove  537  and the fixing rib  515 , and the edge skirt  535  may be plated with gold or another conductive metal. Instead of a conductive metal, the cathode terminal  513  of the bare cell, the cathode terminal acceptor  539 , the contact portions of the U-shaped groove  537  and the fixing rib  515 , and the edge skirt  535  may be coated with a conductive adhesive, such as silver paste. The conductive adhesive generally reduces a contact resistance and has a high adhesive strength. Or, a medium layer structure may be formed to reduce the contact resistance between the fixing rib  515  and the groove  537 , or any of the other contact portions. Then, the protective circuit assembly  530  is coupled to the bare cell  510  through these processes, or a combination thereof, to form a simple pack battery. 
     A wrapping material (not shown) may be additionally provided on the assembly of the bare cells and the protective circuit, or the bare cells may be individually wrapped. Tubing may be used as a wrapping material. 
       FIG. 4A  is a plan view illustrating a cap plate according to aspects of the invention, and  FIG. 4B  is a cross-sectional view illustrating a cross section B-B′ of the cap plate of  FIG. 4A . 
     Referring to  FIGS. 4A and 4B , a fixing rib  340  is formed in a “U” shape on the outer surface of the cap plate  110 , and the fixing rib  340  is adhered to an upper part of the cap plate  110 . It is possible to easily form the fixing rib  340  by fixing a member to the upper part of the cap plate  110  with an adhesive without pressing the cap plate  110 .  FIGS. 4A and 4B  also include the electrolyte injection hole  160 , the vent  190 , and the cathode through-hole  111 , which both extend through the cap plate  110 . The fixing rib  340  and the corresponding groove formed in a battery part (not shown) are step portions. 
       FIG. 5  is a plan view illustrating a cap plated according to aspects of the invention. 
     Referring to  FIG. 5 , fixing ribs  350  are formed in U shapes on both sides of the upper or first surface of the cap plate  110  in the lateral direction. The fixing ribs  350  enable a battery part, including structures corresponding to the fixing ribs  350  on the lower or first surface thereof, to be stably coupled to the upper part of a cap assembly  100  without leaning to one side. The cap plate  110  includes the electrolyte injection hole  160 , the vent  190 , and the cathode through-hole  111 . The fixing ribs  350  and the corresponding grooves formed in a battery part (not shown) are step portions. 
       FIG. 6  is a plan view illustrating a cap plate according to aspects of the invention. 
     Referring to  FIG. 6 , fixing ribs  360  are formed in linear shapes along both long sides of a cap plate  110 . The fixing ribs  360  of the cap plate  110  make it possible to increase the stability of the coupling between the battery part and the cap plate  110 . The cap plate  110  includes the electrolyte injection hole  160 , the vent  190 , and the cathode through-hole  111 . The fixing ribs  360  and the corresponding grooves formed in a battery part (not shown) are step portions. 
       FIG. 7  is a plan view illustrating a cap plate according to aspects of the invention. 
     Referring to  FIG. 7 , fixing ribs  370  are formed in “L” shapes at the four corners of a cap plate  110 . 
     The fixing ribs  370  may be formed on the cap plate  110  by pressing the cap plate to form the fixing ribs  370  with a predetermined shape or by adhering a member of a predetermined shape to the cap plate  110 . The fixing ribs  370 , as described above, provide a space to be formed between a battery part and the cap plate  110 . The space above the cap plate  110  is pressurized so as to prevent an electrolyte from leaking from the electrolyte injection hole  160 . The cap plate  110  also includes the vent  190 . The fixing ribs  370  and the corresponding grooves formed in a battery part (not shown) are step portions. 
     According to aspects of the invention, complementary corresponding step portions are formed between a cap plate of a bare cell and a battery part provided at the upper part of the cap plate, which makes it possible to easily couple the battery part to the bare cell, or a plurality of bare cells, and thus to easily perform subsequent manufacturing processes, such as welding. 
     Further, according to the aspects of the invention, the coupling between the bare cell and the battery part is reliably maintained, which makes it possible to reduce defects in connection due to external impact. 
     Although a few embodiments of the present invention have been shown and described, it would be appreciated by those skilled in the art that changes may be made in this embodiment without departing from the principles and spirit of the invention, the scope of which is defined in the claims and their equivalents.