Abstract:
The secondary battery according to the present invention has a vent deformation accelerator which promotes the operation of a vent formed on a wide side of a can in the cap plate, a bottom side of a can or a narrow side of a can so that the vent operates at the low pressure. Therefore, a secondary battery is provided with a vent which operates at a lower pressure than the operating pressure of existing vents. Also, the vent can be formed relatively thick when the operating vent which operates at the same pressure as the operating pressure of an existing vent so that it can avoid forming a vent having a minute thickness, thereby reducing the manufacturing costs and processing time.

Description:
CLAIM OF PRIORITY 
     This application makes reference to, incorporates the same herein, and claims all benefits accruing under 35 U.S.C. §119 from an application for SECONDARY BATTERY earlier filed in the Korean Intellectual Property Office on the 27 Feb. 2006 and there duly assigned Serial No. 10-2006-0018711. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a secondary battery. More particularly, the present invention relates to a structure promoting venting formed in a wide side of a can to form a vent deformation accelerator that is thinner than other parts in a cap plate, a bottom area of a can, or a narrow side of a can. 
     2. Description of the Related Art 
     Generally, contrary to a primary battery that is impossible to charge, a secondary battery can be charged or discharged so that it is widely used in high tech electronic applications, such as cellular phones, laptop computers, and camcorders. Especially, a lithium secondary battery has 3.6V driving voltage that is three times higher than that of a nickel-cadmium battery or a nickel-metal hydride and is used to power electronic equipment and has a high energy density per unit weight. 
     The lithium secondary battery mainly uses a lithium oxide as a cathode electrode active material and uses a carbon material as a anode electrode active material. Also, a lithium secondary battery is produced in various forms, such as cylinder shaped, square shaped, and pouch shaped. 
     A square shaped battery includes an electrode assembly, a can containing this electrode assembly, and a cap assembly combining with this can. 
     An electrode assembly separator separates the cathode and anode electrode and is arranged between these two electrodes, a cathode electrode and a anode tap respectively extend out from the cathode and anode electrodes. 
     A can is a container of metal material, having a rectangular parallelepiped shape in a square shaped secondary battery, is formed by deep drawing. A can may form a terminal of the battery. The can material can be a suitable aluminum alloy or aluminum that are high conductivity light weight metal materials. The can serves as the container of an electrode assembly and an electrolyte, and has an open upper part to allow insertion of the electrode assembly and is sealed by a cap assembly. 
     The cap assembly includes a cap plate attached to the upper part of the can, an electrode terminal passing through a terminal opening and having a gasket to insulate it from the cap plate, an insulation plate arranged on a lower side of a cap plate, and a terminal plate arranged on a lower side of an insulation plate and supplying an electric current to an electrode terminal. One electrode of the electrode assembly connects to the electrode terminal electrically through an electrode tap and the terminal plate and another electrode is electrically connected to the cap plate or can through a connecting electrode tap. 
     On the other hand, a vent can be formed on one side of a cap plate or on one edge of a wide part of the can. This vent ensures safety of a battery by discharging an internal gas because of preferentially opening, that is separating from the can, when the internal pressure of the battery is increased through overcharging. 
     However, some problems of such a vent are as follows. 
     First of all, a vent formed in a cap plate is a thinner part of a cap plate, the thickness of the edge of the vent where one can expect separating when the internal pressure of the battery is increased through overcharging is only a number of micrometers. Accordingly, designing a secondary battery that includes a vent operating at a lower pressure than the operating pressure of existing vents has a limitation. Also, there are some problems such as requiring accurate forming operations, increasing manufacturing costs, and delaying processing time to form a vent of minute thickness. Also, when an internal pressure is increased when changing the form of the can, there are disadvantages in that it cannot ensure safety of the can effectively because it can not handle a changing pressure of an internal part of the can. 
     On the other hand, a vent formed in a edge of the wide part of a can is a part that is formed to contain a groove of regular depth in a shape of an open-loop of a circle, a thickness of the vent where one can expect a change when the battery has a problem of is only several tens of micrometers. Therefore, a secondary battery including a vent that operates at a lower pressure than operating pressures of existing vents has a limitation as to design. Also, to form the vent to have an accurate thickness, there are some problems such as requiring accurate forming operations, increasing manufacturing costs, and delaying processing time. 
     SUMMARY OF THE INVENTION 
     The present invention, in order to solve the above-described problems, effectively prevents danger from an explosion of a can with a sensitive reacting of the vent at a low internal pressure of the can, provides more time in manufacture processing and design of the vent, and decreases unit cost by simplifying manufacturing processes. 
     The present invention provides a secondary battery including: a can having one side open and including an electrode assembly; a cap assembly having a cap plate attached to the open upper side of the can; a vent arranged on a wide side surface of the can; and a vent deformation accelerator arranged on one of a narrow side of the can or on a bottom side of the can or on the cap plate, the vent deformation accelerator being thinner than other parts of the battery. 
     The vent is preferably arranged on a closed corner portion among four corner portions of the wide side surface of the can by the vent deformation accelerator. The vent is preferably arranged in a diagonal direction of the wide side surface of the can. The vent preferably has a shape of one of one side of an open pentagon or an open circle loop. 
     The shape of the vent is preferably determined according to creases produced on a corner portion of the can when transformed by internal pressure in the can. The shape of the vent is preferably one of ‘           ’ or ‘         ’, or ‘         ’ or ‘         ’.
     The vent preferably includes a depressed notch. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       A more complete appreciation of the present invention and many of the attendant advantages thereof, will be readily apparent as the present invention becomes better understood by reference to the following detailed description when considered in conjunction with the accompanying drawings in which like reference symbols indicate the same or similar components, wherein: 
         FIG. 1  is an exploded perspective view of a secondary battery of an embodiment of the present invention; 
         FIGS. 2A and 2B  are respectively a plane figure and a sectional drawing of a cap assembly of the secondary battery of  FIG. 1 ; 
         FIG. 3  is a view of a secondary battery before and after swelling thereof; 
         FIG. 4  is a tension stress distribution drawing of a wide side of the can, the stress being caused by an internal pressure of the can; 
         FIGS. 5A to 5D  are perspective views of before and after swelling of a secondary battery of another embodiment of the present invention; 
         FIG. 6  is a view of a secondary battery of another embodiment according to the present invention before and after swelling thereof; and 
         FIG. 7  is a view of a secondary battery of still another embodiment according to the present invention before and after swelling thereof. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Hereinafter, exemplary embodiments of the present invention are described with reference to the accompanying drawings. 
       FIG. 1  is an exploded perspective view of a secondary battery of an embodiment of the present invention. 
     As illustrated in  FIG. 1 , a secondary battery  10  includes an electrode assembly  12 , a can  11  containing the electrode assembly  12 , and a cap assembly  100  attached to the can  11 . 
     The electrode assembly  12  has a cathode electrode  13  and a anode electrode  15  of a wide flat shape to increase the battery capacity and a separator  14  arranged between the cathode electrode  13  and the anode electrode  15 , these elements being laminated and wrapped to form a ‘Jelly Roll’ configuration. The anode electrode  15  and the cathode electrode  13  can be respectively formed with a carbon coating that is a anode electrode active material and a cobalt acid lithium that is a cathode electrode active material and collectors formed of a copper and aluminum foil. The separator  14  is formed of polyethylene, polypropylene, or co-polymer of polyethylene and polypropylene. The separator  14  prevents short circuits between electrode plates and is formed to be wider than the cathode electrode  13  and the anode electrode  15 . The electrode assembly  12  includes a cathode electrode tap  16  and a anode electrode tap  17  that are respectively connecting to the two electrodes. The cathode electrode tap  16  and anode electrode tap  17  are wrapped with insulation tape  18  to prevent short circuits between the electrodes  13  and  15  in the border portions thereof extending outside of the electrode assembly  12 . 
     As illustrated in  FIG. 1 , the can  11  is a metal material container of a rectangular parallelepiped shape and is formed by deep drawing, for example. Therefore, the can can serve as a terminal. The can material should be a light high conductivity metal, such as aluminum or an aluminum alloy. The can  11  receives the electrode assembly  12  and an electrolyte via the open upper part thereof which is sealed by the cap assembly  100 . A vent  200  is formed in the wide side of the can and is described in detail later. 
     The cap assembly  100  includes a cap plate  110 , an electrode terminal  130 , an insulation plate  140 , and a terminal plate  150 . A terminal opening  111  is formed in the cap plate  110 , an electrode terminal  130  passes through the terminal opening  111  and includes a gasket  120  to insulate it from the cap plate  110 . An insulation plate  140  is arranged on the bottom side of the cap plate  110  and a terminal plate  150  is arranged on the bottom side of the insulation plate  140 . The terminal plate  150  is connected to the bottom part of the electrode terminal  130 . 
     The anode electrode  15  of the electrode assembly  12  is electrically connected to the electrode terminal  130  through the anode tap  17  and the terminal plate  150 . In the case of the cathode electrode  13  of the electrode assembly  12 , the cathode tap  16  is welded to the cap plate  110  or the can  11 . An insulation case  190  is arranged underneath the terminal plate  150 . On the other hand, a battery can be designed with a differing polarity. 
     A vent  116  is formed on one side of the cap plate  110  and is discussed in detail later, and an electrolyte injection hole  112  is formed on the other side of the cap plate  110  to inject an electrolyte into the can  11 ; a seal  160  is formed to seal the electrolyte injection hole  112  after an electrolyte has been injected. 
     There are various embodiments of the seal  160 . For example, a ball that has larger diameter than the electrolyte injection hole  112  can be arranged at the entrance of the electrolyte injection hole  112  and after forming the seal  160  by mechanically pressing the ball into the electrolyte injection hole  112 , the electrolyte injection hole  112  can then be sealed by welding through the edge of the seal  160 . Also, after covering the top of the electrolyte injection hole  112  with a thin sealing plate that is larger than the electrolyte injection hole  112 , the electrolyte injection hole  112  can be sealed by welding through the edge of the sealing plate. 
     A vent  200  is formed on the wide side of the can  11  and a vent deformation accelerator  116  formed on one side of the cap plate  110  to improve the operation of the vent  200 . 
       FIGS. 2A and 2B  are respectively a plane figure and a sectional drawing of a cap assembly of the secondary battery of  FIG. 1 .  FIG. 3  is a view of a secondary battery before and after swelling thereof.  FIG. 4  is a tension stress distribution drawing of a wide side of the can, the stress being caused by an internal pressure of the can. 
     As illustrated in  FIG. 3 , according to an embodiment of the present invention, the vent  200  is formed on the wide side  11   a  of the can  11  and the vent deformation accelerator  116  that is thinner than other parts is formed on one side of the cap plate  110 . 
     In this case, the vent  200  gets to open ahead of the vent deformation accelerator  116  due to the internal pressure of a can. Namely, the opening pressure of the vent  200  is lower than the opening pressure of the vent deformation accelerator  116 . 
     The vent  200  can secure the safety of a battery through releasing the internal gas by opening preferentially rather than other parts rupturing when the pressure is increased by the internal gas of the battery through overcharging. 
     The production of gas in the can is because of the carbonic acid lithium (Li 2 CO 3 ) that is used for forming a cathode electrode active material, such as cobalt acid lithium (LiCoO 2 ). Excess carbonic acid lithium remains in the cobalt acid lithium cathode electrode active material without reacting and after that, carbonic acid is produced by the carbonic acid lithium when the battery voltage is high and heat is emitted due to overcharging. A swelling in the can occurs by the produced carbonic acid gas and the vent  200  opens and lets out the internal gas out if the swelling is serious. 
     The swelling can be solved if a lesser amount of carbonic acid lithium remains. Currently, too much carbonic acid lithium remains because cobalt oxide (CoO 2 ) still remains in the cathode electrode active material, corrodes both electrodes, and flows out to the electrolyte during charging that results in cobalt extraction at the anode electrode and results in more danger by causing an internal short circuit. 
     As illustrated in  FIG. 4 , a tension stress distribution drawing of the wide side  11   a  of a swelling can (the can has a 48.7 mm long side and a 33.8 mm short side) due to internal gas, the tension stress is increased on an edge of the can  21 , a flat part  22 , a first edge  23 , and a second edge  24 . Namely, large tension stresses occur in the edges  23  and  24  when the can is swelling due to the pressure of the internal gas. 
     Comparing  FIG. 3  with  FIG. 4 , the edges  23  and  24  that have very large tension stresses in  FIG. 4  correspond to the near edges where three creased lines meet in  FIG. 3  due to swelling. 
     The vent  200  is formed very close to the edge by the vent deformation accelerator  116  among creased four edge parts when the can expands due to internal pressure. As illustrated in the tension stress distribution drawing of  FIG. 4 , the reason that it is formed by the edge is because the tension stress is high there, and the reason that it is formed very close to the edge by the vent deformation accelerator  116  is that because the vent deformation accelerator  116  is thinner than other parts of the swelling cap plate  110 . 
     As illustrated in  FIG. 3 , the vent deformation accelerator  116  is formed on the right side of the cap plate  110  that is formed on the upper side of the battery, the vent  200  is formed on the right upper edge of the wide side  11   a  of the can  11  by the vent deformation accelerator  116 . 
     Therefore, the vent deformation accelerator  116  changes before other parts of the cap plate  110  due to the increasing in the internal pressure causing swelling, the tension stress being highest at the upper right edge the wide side  11   a  of the can  11 . According to this, as illustrated in  FIG. 3 , the upper right edge of the battery changes more than the other parts of the battery. 
     The vent  200  is vertically formed in a diagonal direction on the wide side  11   a  of the can. Namely, the vent  200  is formed to vertically cross the wrinkle in a diagonal direction of the can which is formed when the can expands due to internal pressure. For example, the vent can be formed as one side of an open pentagon or circle shaped open loop. 
     A vent can be formed to correspond to wrinkle formed at the edges when a can changes due to internal pressure as show in the  FIGS. 5A to 5D . A vent can be formed ‘           ’-type ( 200 A), ‘         ’-type ( 200 B), ‘         ’-type ( 200 C), or ‘         ’-type ( 200 D) when a wide side of a can looks toward the front side. Likewise, in case the shape of a vent corresponds to a wrinkle, a vent can be effectively open.
     Also, a vent can be formed as a notch. A vent can be formed by a regular depth groove with a notch using etching, electronic molding, or pressing. In this case, when a notch is formed by etching, electronic molding, or pressing, occurring pressure error or inferiority of operation distribution should not occur when it separates by internal pressure with regular the shape or depth. A vent formed by notch can be opened easily by internal pressure of inside of a can. 
     Also, even though this embodiment shows a vent deformation accelerator  116  in the shape of an oval, the present invention is not limited thereto and can be applied to a vent deformation accelerator  116  of various shapes. 
       FIG. 6  is a view of a secondary battery of another embodiment of the present invention before and after swelling. 
     As illustrated in  FIG. 6 , a vent deformation accelerator  116 ′ is formed in the left side of the bottom side  11   b  of a can; the vent deformation accelerator  116 ′ is thinner than the rest of the bottom side  11   b  of the can and therefore changes first when the battery is swelling, and from this change, a tension stress that is bigger than that of other edges is applied to the vent  200 ′ formed on the left bottom part. As illustrated in  FIG. 6 , the left and bottom side of the battery changes more than other parts of the battery. 
       FIG. 7  is a view of a secondary battery of still another embodiment according to the present invention before and after swelling thereof. 
     As illustrated in  FIG. 7 , a vent deformation accelerator  116 ″ is formed on the upper part of a narrow side  11   c  of the can; the vent deformation accelerator  116 ″ is thinner than the rest of the bottom side  11   b  of the can and therefore changes first when the battery is swelling, and from this change, a tension stress that is bigger than that of other parts is applied to a vent  200 ″ formed on the left bottom part. As illustrated in  FIG. 7 , the left bottom side of a battery changes more than other parts of the battery. 
     The secondary battery according to the present invention lets a vent operate at a low pressure to form a vent deformation accelerator that promoted operation of a vent formed in the wide side of a can in the cap plate or bottom side or narrow side of a can. Therefore, a secondary battery including a vent that operates at a lower pressure than existing vent operation pressures can be provided.