Abstract:
A rechargeable battery that prevents a concentration of stress on a coupling portion of a lead tab and a cap assembly at a time of bending the lead tab so as to not damage the coupling portion includes: an electrode assembly having a first electrode, a second electrode, and a separator interposed between the first and second electrodes; a case to receive the electrode assembly and having an open top portion; a cap assembly arranged on the top portion of the case; a lead tab having one end affixed to the cap assembly to electrically connect the cap assembly to the first electrode; and a stopper fixed to the cap assembly and having one end arranged on the lead tab, the stopper allowing a portion of the lead tab contacting the one end of the stopper to be bent when the lead tab is bent.

Description:
CLAIM OF PRIORITY 
       [0001]    This application makes reference to, incorporates the same herein, and claims all benefits accruing under 35 U.S.C. §119 from an application earlier filed in the Korean Intellectual Property Office on the 19 th  of Jan. 2007 and there duly assigned Serial No. 10-2007-0006173. 
       BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The present invention relates to a rechargeable battery and its method of manufacture, and more particularly, the present invention relates to a rechargeable battery having an enhanced lead tab coupling structure and its method of manufacture. 
         [0004]    2. Description of the Related Art 
         [0005]    Rechargeable batteries can repeatedly charge and discharge due to a reversible transformation between chemical energy and electrical energy thereof. Nickel-cadmium batteries, Nickel-hydrogen batteries, and lithium rechargeable batteries are widely used rechargeable batteries. The lithium rechargeable battery has an operating voltage of 3.6V or more. The operating voltage of the lithium-cadmium battery is three times higher than that of the nickel-cadmium battery or the nickel-hydrogen battery. In addition, the lithium rechargeable battery has a high energy density per unit weight. Therefore, recently, the lithium rechargeable battery has been widely used as a power source for portable electronic apparatuses. The lithium rechargeable battery is classified as a lithium-ion rechargeable battery, a lithium-ion polymer battery, and a lithium polymer battery. 
         [0006]    A typical rechargeable battery includes an electrode assembly having an anode, a cathode, and a separator disposed between the anode and the cathode, a case containing the electrode assembly, and a cap assembly coupled to the case to seal the case. The anode and the cathode are provided with respective uncoated anode and cathode parts that are not coated with an activation material. The uncoated anode and cathode parts are disposed in different directions. 
         [0007]    The uncoated cathode part is coupled to a cathode collector plate electrically connected to the case, and the uncoated anode part is coupled to an anode collector plate electrically connected to the cap assembly. 
         [0008]    The cap assembly and the anode collector plate are connected to each other by a lead tab made of a conductive metal. The lead tab is welded to the cap assembly and the anode collector plate. The lead tab in a bent state is disposed between the cap assembly and the anode collector plate. 
         [0009]    However, conventionally, when the lead tab is subject to a bending process, stress is concentrated on a coupling portion of the lead tab and the cap assembly. Therefore, the coupling portion may be damaged. Accordingly, the damage may cause degradation in performance of the rechargeable battery. Moreover, if the coupling portion is broken, the anode and the cap assembly are electrically disconnected, so that the rechargeable battery cannot function. 
       SUMMARY OF THE INVENTION 
       [0010]    The present invention has been made in an effort to provide a rechargeable battery having advantages of preventing concentration of stress on a coupling portion of a lead tab and a cap assembly at a time of bending the lead tab so as not to damage the coupling portion. 
         [0011]    An exemplary embodiment of the present invention provides a rechargeable battery including: an electrode assembly having a first electrode, a second electrode, and a separator interposed between the first and second electrodes; a case to contain the electrode assembly and including an open top portion; a cap assembly disposed on the top portion of the case; a lead tab including one end affixed to the cap assembly to electrically connect the cap assembly to the first electrode; and a stopper affixed to the cap assembly and having one end arranged on the lead tab, the stopper facilitating a portion of the lead tab contacting the one end of the stopper to be bent when the lead tab is bent. 
         [0012]    The one end of the stopper may be disposed on a portion of the lead tab separated from the portion of the lead tab affixed to the cap assembly. The one end of the stopper may be disposed on the portion of the lead tab affixed to the cap assembly. 
         [0013]    The cap assembly may include a cap plate, and one end of the lead tab may be affixed to an edge of one surface of the cap plate. 
         [0014]    The stopper may be fixed to the cap assembly by welding. In addition, the stopper may be welded and fixed to a portion of the cap assembly to which the lead tab is welded. 
         [0015]    Another embodiment of the present invention provides a rechargeable battery including: an electrode assembly having a first electrode, a second electrode, and a separator interposed between the first and second electrodes; a case to receive the electrode assembly and including an open top portion; a cap assembly disposed on the top portion of the case and including a cap plate; and a lead tab connecting the cap plate to the first electrode, wherein a portion of the lead tab separated from one end thereof is affixed to an edge of one surface of the cap plate by, and wherein an end of a first portion of the lead tab, disposed on one side of the portion of the lead tab affixed to the cap plate, is bent toward a second portion of the lead tab disposed on an opposite side thereof. 
         [0016]    The end of the first portion of the lead tab may be disposed on the portion of the lead tab affixed to the cap plate. In addition, the end of the first portion of the lead tab may be disposed on a portion of the second portion separated from the portion of the lead tab affixed to the cap plate. 
         [0017]    The rechargeable battery may further include a first electrode collector plate disposed on an upper portion of the first electrode to be electrically connected to the first electrode, wherein the lead tab is coupled to a lead member connected to the first electrode collector plate. 
         [0018]    Yet another embodiment of the present invention provides a method of manufacturing a rechargeable battery including: forming a first electrode, a cap plate, and a lead tab to electrically connect the first electrode to the cap plate; affixing a portion of the lead tab separated from one end thereof to an edge of one surface of the cap plate; bending an end of a first portion of the lead tab, disposed on one side of the portion of the lead tab affixed to the cap plate, toward a second portion of the lead tab, disposed on an opposite side thereof; and bending a portion of the second portion contacting the first portion when bending the second portion. 
         [0019]    In bending the first portion of the lead tab, the end of the first portion may be disposed on the portion of the lead tab affixed to the cap plate. 
         [0020]    In bending the first portion of the lead tab, the end of the first portion may be disposed on a portion of the second portion separated from the portion of the lead tab affixed to the cap plate. 
         [0021]    The lead tab may be affixed to the cap plate by welding. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0022]    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: 
           [0023]      FIG. 1  is an exploded perspective view of a rechargeable battery according to a first embodiment of the present invention. 
           [0024]      FIG. 2  is a partially enlarged cross-sectional view of  FIG. 1 . 
           [0025]      FIG. 3  is a cross-sectional view of a rechargeable battery according to a second embodiment of the present invention. 
           [0026]      FIG. 4  is a cross-sectional view of a rechargeable battery according to a third embodiment of the present invention. 
           [0027]      FIG. 5  is a flowchart for explaining a rechargeable battery manufacturing method according to an embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0028]    Hereinafter, exemplary embodiments of the present invention are described in detail with reference to the accompanying drawings in order for a person ordinarily skilled in the art to easily implement the present invention. The present invention may be modified in various different ways, and is not limited to the described embodiments. For clarity, description of some constructions and elements not directly related to the present invention have been omitted. Like reference numerals denote like elements. Detailed descriptions of well-known features have been omitted. 
         [0029]      FIG. 1  is an exploded perspective view of a rechargeable battery  100  according a first embodiment of the present invention. In the first embodiment, a lithium ion rechargeable battery is used as an example of the rechargeable battery  100  for explaining the principles of the present invention. However, the present invention is not limited to the lithium ion rechargeable battery. 
         [0030]    As shown in  FIG. 1 , the rechargeable battery  100  includes an electrode assembly  110 , a case  120 , and a cap assembly  140 . 
         [0031]    The electrode assembly  110  includes a first electrode (anode)  114  formed by applying an anode activation material to a collector plate, a second electrode (cathode)  112  formed by applying a cathode activation material to a collector plate, and a separator  113  disposed between the anode  114  and the cathode  112  to prevent a short-circuit therebetween. 
         [0032]    More specifically, the cathode  112  is constructed by coating a slurry-type activation material layer in which a cathode activation material powder, a cathode binder, and a binding material are mixed on a collector plate, such as a copper plate. The cathode activation material powder may be formed by using, as a main material, a carbon material such as natural graphite, artificial graphite, a graphite-type carbon, a non-graphite-type carbon, or a combination thereof. 
         [0033]    An uncoated cathode part  112   a  that is not coated with the activation material layer is formed along a lower edge of the cathode  112 . The uncoated cathode part  112   a  contacts and is connected to a cathode collector plate  132  disposed at the bottom of the case. Accordingly, the cathode  112  is electrically connected to the case  120 , so that the case  120  can function as a cathode terminal of the rechargeable battery. 
         [0034]    On the other hand, the anode  114  is constructed by coating a slurry-type activation material layer in which an anode activation material powder, an anode binder, and an anode conductive additive are mixed on a collector plate, such as an aluminum plate. The anode activation material powder may be formed by using a lithium metal oxide such as LiCoO 2 , LiMnO 2 , LiNiO 2 , LiCrO 2 , and LiMn 2 O 4 . 
         [0035]    An uncoated anode part  114   a  that is not coated with the activation material layer is formed along an edge of the anode  114 . The uncoated anode part  114   a  is connected to an anode collector plate  138  that is disposed above the uncoated anode part  114   a.  The anode collector plate  138  is connected to the cap assembly  140  through a lead member  138   a  and a lead tab  150 . 
         [0036]    The separator  113  has functions of separating the cathode  112  from the anode  114  and providing a transport channel for lithium ions. The separator may be constructed of a single-layered film of polyethylene, polypropylene, or polyvinylidene fluoride, or a multi-layered film formed of two or more layers thereof. In addition, the separator may be constructed as a complex multi-layered film, such as a two-layered separator of polyethylene/polypropylene, a three-layered separator of polyethylene/polypropylene/polyethylene, and a three-layered separator of polypropylene/polyethylene/polypropylene. 
         [0037]    The electrode assembly  110  is formed by sequentially stacking the cathode  112 , the separator  113 , and the anode  114 , providing a central bar to one end of the stacked structure, and trimming the stacked structure into a substantially cylindrical shape. The electrode assembly  110  is inserted into the case  120 , and the central bar is drawn out from the electrode assembly  110 . A center pin (not shown) is inserted into a hollow portion formed by drawing out the central bar. 
         [0038]    The central pin prevents deformation of the electrode assembly  10  during a charge or discharge period of the rechargeable battery  100 . The central pin has a shape of a hollow cylinder. The central pin may be made of iron, copper, nickel, a nickel alloy, or other metals. In addition, the central pin may be made of a polymer. 
         [0039]    Alternatively, without drawing out the aforementioned central bar from the electrode assembly  110 , the central bar may be used as a substitute for the central pin. Such a modification is well-known to a person of ordinary skill in the art. 
         [0040]    The case  120  has a substantially cylindrical space that contains the electrode assembly  110 . The case  120  is made of a conductive metallic material such aluminum, an aluminum alloy, and nickel-coated steel. The top portion of the case  120  is initially open, so that the electrode assembly  110  can be inserted into the case  120  through the open top portion. 
         [0041]    The cap assembly  140  is coupled to the open top portion of the case  120  to seal the case  120 . During a process of coupling the case  120  to the cap assembly  140 , a bead portion  123  and a crimp portion  125  are formed in the case  120 . 
         [0042]    In addition, an electrolyte solution (not shown) is injected into the case  120 . Lithium ions generated by an electrochemical reaction between the cathode  112  and anode  114  during the charging and discharging periods can be transported due to the electrolyte solution. 
         [0043]    The cap assembly  140  includes a positive temperature coefficient element  141 , a safety vent  142 , an electrode cap  143 , a gasket  144 , an insulator  145 , a cap plate  146 , and a sub-plate  147 . 
         [0044]    The gasket  144  is disposed between the case  120  and the electrode cap  143 , the positive temperature coefficient element  141 , and the safety vent  142  to surround circumferences of the electrode cap  143 , the positive temperature coefficient element  141 , and the safety vent  142 . Therefore, the gasket  144  isolates the electrode cap  143 , the positive temperature coefficient element  141 , and the safety vent  142  from the case  120 . 
         [0045]    The safety vent  142  has a hollow protrusion portion  142   a  at the central portion thereof. The safety vent  142  is electrically connected to the anode  114  through the cap plate  146 , the sub-plate  147 , the lead tab  150 , and the anode collector plate  138 , which are disposed under the safety vent  142 . For the electrical connection to the anode  114 , the protrusion portion  142   a  is fixed to the sub-plate  147  by welding, and the lead tab  150  is fixed to the cap plate  146  and the lead member  138   a  of the anode collector plate  138  by welding. 
         [0046]    When an internal pressure of the rechargeable battery  100  increases to a predetermined pressure or more due to some problem, the safety vent  142  is designed to be electrically disconnected from the anode  114 . More specifically, when the internal pressure of the rechargeable battery  100  increases excessively, the-protrusion portion  142   a  of the safety vent  142  and the welding portion of the sub-plate  147  are disconnected due to the increasing internal pressure. Therefore, the safety vent  142  can be electrically disconnected from the anode  114  by the insulator  145  disposed under the safety vent  142 . Moreover, when the internal pressure of the rechargeable battery  100  further increases, the safety vent  142  is ruptured. A gas in the rechargeable battery  100  can be vent through the ruptured portion of the safety vent  142  and a venting hole  143   a.    
         [0047]    The positive temperature coefficient element  141  is connected to an upper portion of the safety vent  142 . Electrical resistance of the positive temperature coefficient element  141  increases to almost infinity when the temperature of the element  141  is over a predetermine temperature. Therefore, when the temperature of the rechargeable battery  100  is more than a predetermined temperature, a flow of the charging and discharging current can be stopped by using the positive temperature coefficient element  141 . However, when the temperature of the rechargeable battery  100  drops down to the predetermined temperature, the electrical resistance of the positive temperature coefficient element  141  decreases, so that the functions of the rechargeable battery  100  can be recovered. 
         [0048]    The rechargeable battery  100  according to the first embodiment includes separate safety elements for preventing over-charge, over-discharge, over-heat, and over-current as well as the aforementioned safety vent  142  and positive temperature coefficient element  141 . 
         [0049]    The venting hole  143   a  is provided to a side of the electrode cap  143 . The electrode cap  143  is connected to an upper portion of the positive temperature coefficient element  141  to function as an anode terminal for applying current outwards. 
         [0050]    The insulator  145  is disposed between the safety vent  142  and the cap plate  146 . A hole is formed to penetrate central portions of the insulator  145  and the cap plate  146 , and the protrusion portion  142   a  of the safety vent  142  penetrates the hole to contact with the sub-plate  147 . Except for the protrusion portion  142   a  of the safety vent  142 , the other portions thereof are electrically isolated from the cap plate  146 . In such a construction, when a welding portion of the protrusion portion  142   a  of the safety vent  142  and the sub-plate  147  is disconnected, the safety vent  142  can be electrically disconnected from the anode  114 . 
         [0051]    One side of the lead tab  150  is fixed on the cap plate  146 , and the other side thereof is fixed to the lead member  138   a  of the anode collector plate  138 , so that the cap plate  146  can be electrically connected to the anode  114 . The lead tab  150  maybe fixed to the cap plate  146  and the lead member  138   a  by welding. 
         [0052]    The lead member  138   a  may be integrally formed with the anode collector plate  138 . Alternatively, the lead member  138   a  may be fixed to the anode collector plate  138  by welding a separately-formed member to the anode collector plate  138 . 
         [0053]      FIG. 2  is a cross-sectional view of the lead tab  150  coupled to the cap assembly  140 . The coupling structure of the lead tab  150  is described in detail below with reference to  FIG. 2 . 
         [0054]    A portion of the lead tab  150  spaced apart from one end thereof is fixed to an edge of one surface of the cap plate  146  by welding. An end of a first portion  151  of the lead tab  150 , arranged on one side of the welding portion  160 , is bent toward a second portion  152  of the lead tab  250  arranged on the opposite side thereof. Due to the bending, the end of the first portion  151  is arranged on the second portion  152 . 
         [0055]    The other end of the second portion  152  of the lead tab  150  opposite to the end connected to the welding portion is connected to the lead member  138   a  of the anode collector plate  138  disposed under the cap plate  146 . The lead member  138   a  is integrally formed with the anode collector plate  138 . However, the present invention is not limited thereto. 
         [0056]    The second portion  152  of the lead tab  150  is bent to be coupled with the lead member  138   a  (see  FIG. 1 ). When the second portion  152  is bent, a portion of the second portion  152  contacting the end of the first portion  151  is bent. Conventionally, when the second portion  152  of the lead tab  150  is bent, the welding portion  160  is bent, so that the welding portion  160  may be damaged. However, according to the first embodiment, when the second portion  152  is bent, the portion  152   a  that is separated by a predetermined distance from the welding portion  160  is bent. Accordingly, concentration of stress on the welding portion  160  is prevented. 
         [0057]      FIG. 3  is a cross-sectional view of a portion of a rechargeable battery according to a second embodiment of the present invention. As shown in  FIG. 3 , an end of a first portion  251  of a lead tab  250  is arranged on the welding portion  160 . Other technical features except for the aforementioned construction are the same as those of the first embodiment. 
         [0058]    According to the second embodiment, when a second portion  252  of the lead tab  250  is bent, a portion  252   a  of the second portion  252  separated by a predetermined distance from the welding portion  160  is bent to contact an end of the first portion  251  of the lead tab  250 . Accordingly, when the second portion  252  is bent, concentration of stress on the welding portion  160  is prevented. 
         [0059]      FIG. 4  is a cross-sectional view of a rechargeable battery according to a third embodiment of the present invention. Referring to  FIG. 4 , an end of a lead tab  350  is fixed on an edge of one surface of the cap plate  146  by welding. The welding may be laser welding or resistance welding. The other end of the lead tab  350  is coupled to the lead member  138   a  (see  FIG. 1 ) of the anode collector plate  138  (see  FIG. 1 ). 
         [0060]    A stopper  351  is fixed to the cap plate  146  by welding. The stopper  351  is vented toward the lead tab  350  so that an end of the stopper  361  is disposed on a portion of the lead tab  350  separated by a predetermined distance from the welding portion  360 . Alternatively, the one end of the stopper  351  may be disposed on the welding portion  360 . In addition, the stopper  351  maybe connected to the welding portion, that is, the coupling portion of the cap plate  146  and the lead tab  350  as well as the cap plate  146 . 
         [0061]    The lead tab  350  is bent to be coupled with the lead member  138   a.  When the lead tab  350  is bent, the lead tab  350  is bent at the portion  350   a  contacting the one end of the stopper  351 . 
         [0062]    Conventionally, when the lead tab  350  is bent, the welding portion  360  is bent, so that the welding portion  360  may be damaged. According to the third embodiment, when the lead tab  350  is bent, the portion  350   a  that is separated by a predetermined distance from the welding portion  360  is bent, so that concentration of stress on the welding portion  360  is prevented. 
         [0063]      FIG. 5  is a flowchart for explaining a rechargeable battery manufacturing method according to an embodiment of the present invention 
         [0064]    Referring to  FIG. 5 , firstly, a first electrode, a cap plate, and a lead tab for electrically connecting the first electrode and the cap plate are formed (not shown). 
         [0065]    Next, a portion of the lead tab separated by a predetermined distance from one end thereof is welded to an edge of one surface of the cap plate (S 10 ). 
         [0066]    Next, an end of a first portion of the lead tab, arranged on one side of the welding portion, is bent toward a second portion of the lead tab arranged on the opposite side (S 20 ). 
         [0067]    Subsequently, the one end of the first portion is arranged on a portion of the second portion separated by a predetermined distance from the welding portion (S 30 ). Alternatively, the one end of the first portion may be arranged on the welding portion of the lead tab and the cap plate. 
         [0068]    Next, the second portion of the lead tab is bent (S 40 ). The portion of the second portion separated by a predetermined distance from the welding portion is bent to contact the end of the first portion. Accordingly, concentration of stress on the welding portion  160  is prevented. 
         [0069]    Finally, the second portion of the lead tab is coupled to the lead member of the anode collector plate by welding (S 50 ). 
         [0070]    According to the rechargeable battery manufacturing method, when the lead tab is bent, the coupling portion of the lead tab is not bent, but rather a portion that is separated from the coupling portion is bent. As a result, damage to the coupling portion is prevented. 
         [0071]    Although the present invention can be implemented with various embodiments, the embodiments are exemplified for description of the principle of the present invention. However, the present invention is not limited thereto. Therefore, the present invention is not limited to the aforementioned embodiments, and it will be understood by a person of ordinarily skill in the art that various modifications and changes may be made without departing from the spirit and scope of the present invention. 
         [0072]    As described above, according to the embodiments of the present invention, due to a stopper or a first portion of a lead tab, when the lead tab is bent, concentration of stress on a coupling portion of the lead cap and a cap assembly is prevented. 
         [0073]    In addition, since stress is not concentrated on the coupling portion, a process of bending the lead tab can be easily performed, so that a manufacturing process time can be reduced. 
         [0074]    While this invention has been described in connection with what is presently considered to be practical embodiments, it is to be understood that the present invention is not limited to the disclosed embodiments, but, on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims.