Abstract:
A secondary battery includes: a case; an electrode assembly including a positive electrode, a negative electrode, and a separator interposed therebetween, the electrode assembly being arranged within the case; a cap assembly affixed to the case and adapted to seal the case, the cap assembly being electrically connected to the electrode assembly; and a pair of current collecting plates adapted to be respectively electrically connected to the positive and negative electrodes. Each electrode includes an un-coated region absent an active material, the un-coated region of each electrode contacting its respective current collecting plate. Each un-coated region includes a plurality of independent regions separated from one other, the plurality of independent regions being bent and affixed to their respective current collecting plate.

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 for SECONDARY BATTERY AND ELECTRODES ASSEMBLY earlier filed in the Korean Intellectual Property Office on 23 Jun. 2004 and there duly assigned Serial No. 10-2004-0047012.  
       BACKGROUND OF THE INVENTION  
       [0002]     1. Field of the Invention  
         [0003]     The present invention relates to a secondary battery, and more particularly, to an electrode of an electrode assembly of a secondary battery.  
         [0004]     2. Description of the Related Art  
         [0005]     According to usage and battery capacity, secondary batteries are classified into low-capacity secondary batteries, which are referred to as “small batteries” hereinafter, that use a single battery cell packaged in the form of a pack, and high-capacity secondary batteries, which are referred to as “large batteries” hereinafter, that use scores of battery cells packaged into a battery pack for driving a motor.  
         [0006]     Small batteries are used as the power source for small electronic devices, such as mobile phones, laptop computers, and camcorders, while large batteries are used as the power source for driving motors in hybrid electric vehicles and the like.  
         [0007]     Depending on the external shape, small batteries may be classified into different types, such as square and cylindrical batteries. A small battery generally includes a positive electrode, a negative electrode, and a separator that is interposed as an insulator between the positive electrode and the negative electrode, that are spiral-wound to thereby form an electrode assembly. The electrode assembly is inserted into a cylindrical case to form the battery.  
         [0008]     Each of the positive and negative electrodes of a secondary battery is provided with a conductive lead element for collecting current generated in positive and negative electrodes during the operation of the secondary battery. The lead element induces current generated in the positive and negative electrode to positive and negative terminals.  
         [0009]     When the structure of the small battery is directly applied to a large battery, the operational characteristics of the large battery are not fulfilled with respect to electric capacity and power output. Therefore, a multi-tab structure using a plurality of tabs which are attached to an electrode assembly has been suggested in Japanese Laid-open Patent Application No. 2003-7346. This battery has a plurality of tabs along one direction of electrode assembly and the tabs are combined with an internal terminal which is connected to an external terminal.  
         [0010]     However, such a multi-tab structure is required for many working processes. Especially, the tab has a small unit area and thus limitations for satisfying the output power characteristics required for large batteries.  
         [0011]     Another form of the lead element is a current collecting plate. Since the current collecting plate has a wider unit area than the tap, it can have an increased current collecting efficiency and a higher energy density per unit area than the tap by reducing the space occupied by the tap in the case.  
         [0012]     The current collecting plate, however, has a shortcoming that it is not fixed on an electrode assembly firmly. To be specific, the current collecting plate is usually affixed to the electrode assembly mainly by welding. If the electrode assembly is formed in a shape of a jelly-roll by winding a positive electrode, a negative electrode and a separator, and a current collecting plate is fixed on the electrode assembly by welding, the contact area between the current collecting plate and the electrode assembly is relatively small in the outer part, compared to the contact area in the central part of the electrode assembly. Therefore, the welding is not carried out properly in the outer part and this makes the connection between the current collecting plate and the electrode assembly unstable.  
       SUMMARY OF THE INVENTION  
       [0013]     In order to obviate the problems described above, it is an aspect of the present invention to provide a secondary battery with a lead element firmly affixed to the electrode assembly, the lead element electrically connected to the electrode assembly.  
         [0014]     It is another aspect of the present invention to provide a secondary battery including: a case; an electrode assembly including a positive electrode, a negative electrode, and a separator interposed therebetween, the electrode assembly being arranged within the case; a cap assembly affixed to the case and adapted to seal the case, the cap assembly being electrically connected to the electrode assembly; and a pair of current collecting plates adapted to be respectively electrically connected to the positive and negative electrodes; wherein each electrode includes an un-coated region absent an active material, the un-coated region of each electrode contacting its respective current collecting plate; and wherein each un-coated region includes a plurality of independent regions separated from one other, the plurality of independent regions being bent and affixed to their respective current collecting plate.  
         [0015]     The plurality of independent regions preferably include portions of the respective un-coated region slit at arbitrary intervals in a longitudinal direction of the un-coated region.  
         [0016]     The widths of the independent regions preferably become gradually wider from one side of the respective electrode to the other side of the electrode in the longitudinal direction of the electrode.  
         [0017]     The widths of the independent regions are preferably narrower in a central part of the electrode assembly than in an outer part of the electrode assembly.  
         [0018]     Each un-coated region preferably includes a dependent region adapted to connect its independent regions to form one body.  
         [0019]     The dependent regions are preferably bent.  
         [0020]     The independent regions are preferably bent toward a center of the electrode assembly.  
         [0021]     The independent regions preferably include convex and concave portions arranged in a line end of their respective un-coated region in a longitudinal direction of the un-coated region.  
         [0022]     The widths of the independent regions preferably become gradually wider from one side of the respective electrode to the other side of the electrode in the longitudinal direction of the electrode.  
         [0023]     The widths of the independent regions are preferably narrower in a central area of the electrode assembly than in an outer part of the electrode assembly.  
         [0024]     The convex portions preferably include an angled shape.  
         [0025]     The convex portions alternatively preferably include a round shape.  
         [0026]     The electrode assembly preferably includes a jelly-roll configuration.  
         [0027]     The secondary battery preferably includes a cylindrical battery. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0028]     A more complete appreciation of the present invention, and many of the above and other features and advantages of the present invention, will be readily apparent as the same 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:  
         [0029]      FIG. 1  is a cross-sectional view of a secondary battery in accordance with an embodiment of the present invention;  
         [0030]      FIG. 2  is an exploded perspective view of an electrode assembly in accordance with an embodiment of the present invention;  
         [0031]      FIG. 3  is a plane view of a positive electrode in accordance with an embodiment of the present invention;  
         [0032]      FIG. 4  is a perspective view of a current collecting plate connected to the electrode assembly in accordance with an embodiment of the present invention;  
         [0033]      FIG. 5  is a cross-sectional view of how a positive electrode is connected to a current collecting plate in accordance with a modified embodiment of the present invention; and  
         [0034]      FIGS. 6 and 7  are plane views of positive electrodes in accordance with other embodiments of the present invention. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0035]     In the following detailed description, the following embodiments of the invention have been shown and described, simply by way of illustration. As will be realized, the present invention is capable of modification in various respects, all without departing from the scope of the present invention. Accordingly, the drawings and description are to be regarded as illustrative in nature, and not restrictive.  
         [0036]      FIG. 1  is a cross-sectional view of a secondary battery in accordance with an embodiment of the present invention.  
         [0037]     In the present embodiment, the secondary battery has a shape of a cylinder or a hexahedron, and it is formed by arranging an electrode assembly  20 , which is formed by interposing an insulating separator  21  between a positive electrode  22  and a negative electrode  23  and winding them, into a case  11  having an opening and sealing the opening of the case  11  with a cap assembly  30  and a gasket  32 .  
         [0038]     The case  11  is formed of conductive metal, such as aluminum, an aluminum alloy, and nickel-plated steel. Preferably, the case  11  is formed in a cylindrical shape having a space for housing the electrode assembly  20 , but the present invention is not limited to this shape.  
         [0039]     The electrode assembly  20  is formed by interposing the separator  21  between the positive electrode  22  and the negative electrode  23  and winding them together. The positive electrode  22  and the negative electrode  23  respectively have un-coated regions  22   b  and  23   b , that is, regions not having a coating of an active material. The positive un-coated region  22   b  and the negative un-coated region  23   b  are respectively connected to a positive current collecting plate  50  and a negative current collecting plate  70  for collecting current.  
         [0040]      FIG. 1  is a view of an example where the jellyroll-type electrode assembly  20  is arranged in the case  11  and, hereinafter, the present invention is described based on this example. However, the present invention is not limited to this example.  
         [0041]     The cap assembly  30  is provided with a cap plate  31  having an external terminal  31   a  and the gasket  32  for insulating the case  11  from the cap plate  31 . The cap assembly  30  includes a space for buffering internal pressure and it can further include a vent plate  33  having a safety valve which is ruptured at a predetermined pressure level and releases gas to thereby prevent the battery from exploding. The safety valve is not limited to being formed in the vent plate  33  but rather any location is possible as long as the safety valve can electrically disconnect the electrode assembly  20  from the external terminal  31   a  at the predetermined pressure level.  
         [0042]     The gasket  32 , which is formed of an insulating material, not only seals the case  11  but also electrically insulates the cap assembly  30 , which forms a positive pole, from the case  11 , which forms a negative pole.  
         [0043]     The cap assembly  30  is electrically connected to the electrode assembly  20  of the present invention via a lead line  60 .  
         [0044]     Referring to  FIG. 2 , the electrode assembly  20  is formed by interposing the separator  21  between the positive electrode  22  and the negative electrode  23  and winding them together. The positive electrode  22  and the negative electrode  23  are formed by respectively coating positive and negative current collectors  221  and  231  with corresponding active materials  22   a  and  23   a . The active materials are not applied to the edge of one side of the current collectors  221  and  231 , and the regions not coated with the active materials are referred to hereinafter as un-coated regions  22   b  and  23   b.    
         [0045]     The positive un-coated region  22   b  and the negative un-coated region  23   b  are arranged opposite to each other after the electrode assembly  20  is completed, and protrude from the separator  21 .  
         [0046]     With the electrode assembly  20  formed as above, a positive current collecting plate  50  is arranged to contact the positive un-coated region  22   b  and a negative current collecting plate  70  is arranged to contact the negative un-coated region  23   b . The collecting plates  50  and  70  are respectively electrically connected to the un-coated regions  22   b  and  23   b  by laser welding, for example.  
         [0047]     In order to minimize contact resistance between the un-coated regions  22   b  and  23   b  and the current collecting plates  50  and  70 , the un-coated regions  22   b  and  23   b  are bent toward the center of the electrode assembly  20  so that they contact the current collecting plates  50  and  70  face to face.  
         [0048]      FIG. 3  is a plane view of the electrodes of the electrode assembly in accordance with an embodiment of the present invention. Since the positive electrode  22  and the negative electrode  23  have the same shape, they will be described with reference to the positive electrode  22  hereinafter for the sake of convenience. The description of the positive electrode  22  also applies to the negative electrode  23 .  
         [0049]     Referring to the  FIG. 3 , the un-coated region  22   b  formed along a line end of the positive electrode  22  is cut in a longitudinal direction at arbitrary intervals. That is, part of the un-coated region  22   b  is partially cut by slits  22   c  having an arbitrary length  1 . Thus, the un-coated region  22   b  has a plurality of independent regions  220   b  which are separated from each other and form different bodies of their own and a dependant region  222   b  which connects the independent regions  220   b  and form one body.  
         [0050]     The independent regions  220   b  are where the positive current collecting plate  50  substantially contacts the positive electrode  22  and gets attached thereto by welding, when the positive electrode  22  is electrically connected to the positive current collecting plate  50 .  
         [0051]     To be more specific, the independent regions  220   b  are the part that is bent toward the center of the electrode assembly  20  and contacts and gets attached to the positive current collecting plate  50  face to face, when the electrode assembly  20  is completed (see  FIG. 4 ).  
         [0052]     In accordance with the present embodiment, since the independent regions  220   b  can freely move with the slits  22   c  between them, they can be collectively bent toward the center of the electrode assembly  20  to thereby widen the contact area with the positive current collecting plate  50 .  
         [0053]     The independent regions  220   b  can be formed by widening or narrowing the width gradually in the longitudinal direction of the positive electrode  22 . The independent regions  220   b  of the present embodiment are formed to have the width gradually narrowed as they go from the outer part of the electrode assembly  20  to the center (O) part.  
         [0054]     The widths of the independent regions  220   b  are narrow (W 1 ) in the central part of the electrode assembly  20  and wide (W 2 ) in the outer part of the electrode assembly  20  in consideration that the circumference of the electrode assembly  20  becomes larger as it goes toward the outer part of the electrode  20 , when the electrode assembly  20  is formed by winding the positive electrode  22  in the form of jelly-roll and the independent regions  220   b  are bent toward the center of the electrode assembly  20 . Thus, the independent regions  220   b  can be bent in a fine state without being squashed or entangled, and the contact area to the positive current collecting plate  50  can be widened.  
         [0055]     Therefore, the positive electrode  22  can contact the positive current collecting plate  50  electrically and mechanically due to the positive un-coated region  22   b  having the above structure without any problem.  
         [0056]     When the positive un-coated region  22   b  contacts the positive current collecting plate  50 , not only the independent regions  220   b  but also the dependent region  220   b  of the positive un-coated region  22   b  can be bent and contact the positive current collecting plate  50 . The contact area between the positive un-coated region  22   b  and the positive current collecting plate  50  can be widened further and the current collecting efficiency can be improved.  
         [0057]      FIGS. 6 and 7  are plane views of positive electrodes in accordance with another embodiment of the present invention. In this embodiment, the independent regions  220   b  are formed in convex and concave patterns.  
         [0058]     The convex and concave patterns of the independent regions are described below taking an example of a positive electrode for the sake of convenience in the description of  FIGS. 6 and 7 .  
         [0059]     In accordance with the present embodiment, the independent regions  220 ′ b  and  220 ″ b  are formed in as concave shaped  224 ′ b  and  224 ″ b  and convex shapes  226 ′ b  and  226 ′ b  formed at the line end of the un-coated regions  22 ′ b  and  22 ″ b.    
         [0060]     In other words, the concave regions  224 ′ b  and  224 ″ b  and the convex regions  226 ′ b  and  226 ″ b  are formed in the un-coated regions  22 ′ b  and  22 ″ b  in the present embodiment. Due to the concave regions  224 ′ b  and  224 ″ b , the convex regions  226 ′ b  and  226 ″ b  become independent bodies and they are used as independent regions  220 ′ b  and  220 ″ b .  FIG. 6  shows the convex regions  226 ′ b  formed in an angled shape such as triangle, while  FIG. 7  shows the convex shapes  226 ″ b  formed in a round shape such as half-moon.  
         [0061]     Since the pattern and function of the independent regions  220 ′ b  and  220 ″ b  are the same as that described above, a detailed description of them has been omitted herein.  
         [0062]     In accordance with the present invention, the contact area between the current collecting plate and the electrode assembly is widened to thereby reduce the contact resistance, while increasing the current collecting efficiency to the contrary.  
         [0063]     The secondary battery according to an embodiment of the present invention is useful as the power source for driving a motor which is used for high power electrical devices that requires high power such as electric vehicles, hybrid electric vehicles, cordless vacuum cleaners, motorbikes, and motor scooters.  
         [0064]     While this invention has been described in connection with what is presently considered to be practical exemplary 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.