Patent Publication Number: US-2006008702-A1

Title: Secondary battery

Description:
CROSS REFERENCE TO RELATED APPLICATIONS  
      This application claims priority to and the benefit of Korean Patent Application Nos. 10-2004-0047013, 10-2005-0019038, 10-2005-0053943, and 10-2005-0053961 filed in the Korean Intellectual Property Office on Jun. 23, 2004, Mar. 8, 2005, Jun. 22, 2005, and Jun. 22, 2005, respectively, the entire disclosures of which are incorporated herein by reference.  
     FIELD OF THE INVENTION  
      The present invention relates to a secondary battery, and in particular, to an electrode assembly for a secondary battery.  
     BACKGROUND OF THE INVENTION  
      Secondary batteries are based on a rechargeable mechanism distinguished from that of primary cells where only the irreversible conversion of chemical to electrical energy is made. Secondary batteries may be classified into low-capacity batteries, which use a single battery cell packaged in the form of a pack, and high-capacity batteries, which use scores of battery cells packaged into a battery pack. The low-capacity batteries are used as the power source for small electronic devices such as cellular phones, laptop computers, and camcorders, while the high-capacity batteries are used as the power source for devices such as motors in hybrid electric vehicles and the like.  
      Secondary batteries are formed of various shapes including cylindrical shapes and prismatic shapes. An electrode assembly may include an insulating separator disposed between sheet-type positive and negative electrodes and mounted within a case with a cap assembly fitted to the case.  
      The positive and the negative electrodes are each formed by coating an active material on a current collector. Depending upon the presence or absence of the active material coated on the collector, the region coated with the active material is called “the coated region,” while the region with no active material is called the “uncoated region.” 
      The positive electrode, the separator and the negative electrode are often wound in a jelly roll configuration, such as for a cylindrical-shaped battery, or wound in a jelly roll configuration and pressed, such as for a prismatic-shaped battery.  
      When an electrode assembly is prepared to fabricate a secondary battery, the positive and the negative electrodes are laminated together with the separator, and wound. Sometimes, upon winding the electrode assembly, the initial wound portion may be crumpled, making the final product defective.  
      This problem is encountered because the positive and the negative current collectors that form the electrode assemblies are formed from thin plates, and the rigidity thereof is weak.  
      When the fabricated electrode assembly is defective due to the above problem, the current collector inevitably becomes defective making the secondary battery unreliable.  
      When the above problem is encountered with a secondary battery in a service requiring high power output such as for driving a motor, it is particularly difficult to use such a battery and device failure may result.  
     SUMMARY OF THE INVENTION  
      In accordance with an embodiment of the present invention, a secondary battery is provided in which has a high quality electrode assembly with well-wound electrodes.  
      According to one embodiment of the present invention, a secondary battery includes an electrode assembly with a positive electrode, a negative electrode and a separator disposed between the positive and the negative electrodes, and a case in which the electrode assembly is mounted. At least one of the positive and the negative electrodes has a leading edge with a rigidity reinforcing member.  
      According to an embodiment of the invention, the electrode assembly is formed in the shape of a jelly roll.  
      According to an embodiment of the invention, the electrode has a current collector with an active material layer formed on at least a portion of the current collector. The region of the current collector with the active material is referred to as an “active material region,” and the region without active material is referred to as a “non-active material region.” 
      According to an embodiment of the invention, a non-active material region is formed on the periphery of one side of the current collector along the length of the current collector.  
      According to one embodiment of the invention, a rigidity reinforcing member is also formed on the active material layer.  
      According to various embodiments of the invention, the rigidity reinforcing member may be formed over a non-active material region of the current collector.  
      The rigidity reinforcing member may also be formed to extend over a portion of the active material layer.  
      The active material layer may also be placed on one side surface of the current collector with the rigidity reinforcing member formed on an opposite side surface of the current collector with no active material layer.  
      The rigidity reinforcing member may be a film formed separately from the electrode, and attached to the electrode.  
      The film may be placed only on one side surface of the current collector, or it may be placed on both side surfaces of the current collector while surrounding the leading edge of the current collector.  
      Suitable films are made from polyester, polyimide, polyphenylene sulfide, glass fiber, vinyl chloride and synthetic fibers.  
      The width of the film placed on the surface of the current collector may be from 2 to 15 cm.  
      The film may be attached to the electrode by an adhesive.  
      The rigidity reinforcing member may be formed by overlapping the current collector.  
      The rigidity reinforcing member may be formed by making a portion of the current collector corresponding to the leading edge of the electrode thicker than other portions of the electrode.  
      The rigidity reinforcing member may be structured such that the thickness of the active material layer formed on the current collector corresponding to the leading edge of the electrode is larger than the thickness of the active material layer formed on other portions of the current collector.  
      According to other embodiments of the present invention, a secondary battery includes such an electrode assembly with a positive electrode, a negative electrode and a separator disposed between the positive and the negative electrodes, and a case in which the electrode assembly is mounted. At least one of the positive and the negative electrodes may have a leading edge with a thickness different from the thickness of other portions of the electrode.  
      The thickness of the leading edge of the electrode may be larger than the thickness of other portions of the electrode.  
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       FIG. 1  is a sectional view of a secondary battery according to a first embodiment of the present invention;  
       FIG. 2  is an exploded perspective view of an electrode assembly for the secondary battery according to the first embodiment of the present invention;  
       FIG. 3A  is a partial plan view of a positive electrode for the secondary battery according to the first embodiment of the present invention;  
       FIG. 3B  is a partial plan view of a negative electrode for the secondary battery according to the first embodiment of the present invention;  
       FIGS. 4A, 4B ,  4 C and  4 D illustrate a rigidity reinforcing member for the secondary battery according to the first embodiment of the present invention;  
       FIGS. 5A, 5B  and  5 C illustrate a rigidity reinforcing member for a secondary battery according to a second embodiment of the present invention;  
       FIGS. 6A, 6B  and  6 C illustrate a rigidity reinforcing member for a secondary battery according to a third embodiment of the present invention; and  
       FIGS. 7A and 7B  illustrate a rigidity reinforcing member for a secondary battery according to a fourth embodiment of the present invention. 
    
    
     DETAILED DESCRIPTION  
       FIG. 1  is a sectional view of a secondary battery according to a first embodiment of the present invention. According to this embodiment, an electrode assembly  10  is formed by interposing an insulating separator  13  between positive and negative electrodes  11  and  12 , and winding them. The electrode assembly  10  is mounted within a cylindrical-shaped or hexahedral-shaped case  20  through an opening portion thereof. The opening portion of the case  20  is sealed by a cap assembly  30  via a gasket  31 .  
      The case  20  is formed of a conductive metallic material, such as aluminum, aluminum alloy, or nickel-plated steel. For this embodiment, the case  20  is of a cylindrical shape with an inner space in which the electrode assembly  10  is mounted, but the invention is not limited thereto.  
      The cap assembly  30  includes a cap plate  32  with an external terminal  32   a , and a gasket  31  for insulating the case  20  from the cap plate  32 . The cap assembly  30  may further include a vent plate  33  with a safety vent, which is broken under a predetermined pressure in order to discharge the gas generated in the case  20  and prevent the secondary battery from exploding. However, the safety vent is not limited to that formed at the vent plate  33 , but may be varied in structure provided that it electrically insulates the electrode assembly  10  from the external terminal  32   a  of the cap assembly  30  under the predetermined pressure.  
      The gasket  31  based on an insulating material seals the case  20 , and electrically insulates the cap assembly  30  being the cathode from the case  20  being the anode.  
      The cap assembly  30  is electrically connected to the electrode assembly  10  via a lead element  35 .  
      The electrode assembly for the secondary battery according to the first embodiment of the present invention will be now explained.  
      As shown in  FIG. 2 , with the electrode assembly  10 , a separator  13  is disposed between the positive and negative electrodes  11  and  12 , and spirally wound together. The positive and the negative electrodes  11  and  12  have active material layers formed by coating an active material on current collectors  11   b  and  12   b , respectively.  
      The active material is not coated on the length of one peripheral side of each of current collectors  11  and  12 . That is, the peripheral portions of the current collectors  11  and  12  are uncoated, and therefore, exposed.  
      For explanatory convenience, the regions of the positive and the negative electrodes  11  and  12  with the active material layer will be referred to hereinafter as “active material regions”  11   c  and  12   c , and the regions thereof with no active material will be referred to as the “non-active material regions”  11   a  and  12   a.    
      With the formation of the electrode assembly  10 , the non-active material region  11   a  of the positive electrode  11  and the non-active material region  12   a  of the negative electrode are on opposite sides of the electrode assembly  10  and protrude out past the edges of the separator  13 .  
      A positive current collecting plate  40  is welded to the non-active material region  11   a  of the positive electrode  11 , and a negative current collecting plate  50  is welded to the non-active material region  12   a  of the negative electrode  12 . The positive current collecting plate  40  is also electrically connected to a vent plate  33  of the cap assembly  30  via the lead element  35 , and the negative current collecting plate  50  is welded to the bottom of the case  20  while being electrically connected thereto.  
      As shown in  FIG. 2 , the positive electrode  11 , the negative electrode  12  and the separator  13  are wound around a core  14  in a jelly roll configuration. At least one of the positive and the negative electrodes  11  and  12  is provided with a rigidity reinforcing member so that the inside end of the relevant electrode may be wound tightly around the core  14  without being crumpled.  
      In this embodiment, a rigidity reinforcing member is separately formed at each of the positive and the negative electrodes  11  and  12 . Each rigidity reinforcing member is formed with films  15  attached to one end of each of the positive and the negative electrodes  11  and  12  separately. It should be apparent to one of ordinary skill in the art that that when winding the electrode assembly  10  into a jelly roll configuration with the core  14  at the center, the winding starts at the ends of the positive and negative electrodes  11  and  12  that include the film  15 . Therefore, this end of each of the positive and negative electrodes  11  and  12  will be referred to as the “leading edge.” 
       FIG. 3A  illustrates the embodiment where a film  15  is formed at the positive electrode  11 , and  FIG. 3B  illustrates the case where a film  15  is formed at the negative electrode  12 .  
      In this embodiment, the films  15  are made of a material such as polyester, polyimide, polyphenylene sulfide, vinyl chloride or synthetic fiber, and each is attached to the leading edge of the positive and the negative electrodes  11  and  12 .  
       FIGS. 4A  to  4 D illustrate different variations by which the films  15  are attached to the leading edges of the positive and the negative electrodes  11  and  12 .  
      The films  15 ,  15   a ,  15   b  and  15   c  shown in  FIGS. 4A  to  4 D are provided on one side surface of each of the positive and the negative electrodes  11  and  12 , and attached to the leading edges of the positive and the negative electrodes  11  and  12 .  
      A film  15 ,  15   a  and  15   b , as shown in  FIGS. 4A  to  4 C is placed on the leading edge of each of the positive and the negative electrodes  11  and  12  on the side with the active material regions  11   c  and  12   c.    
      According to  FIG. 4A , the film  15  may be in contact with the active material layer of the current collectors  11   b  and  12   b , or as shown in  FIG. 4B , the film  15   a  may be in a region of the current collectors  11   b  and  12   b  with no active material. Alternatively, as shown in  FIG. 4C , the film  15   b  may contact the current collector at a region with no active material while partially extending over the active material layer.  
      According to  FIG. 4D , the film  15   c  may be provided on the side of the electrode  11 ,  12  opposite the side with the active material layer.  
      An adhesive  16  is used to attach the films  15 ,  15   a ,  15   b  and  15   c  to the leading edges of the electrodes  11  and  12 . In general, the adhesive  16  should not react with the active material of the positive and the negative electrodes  11  and  12 , nor should it react with the electrolyte filled within the case  20 . An acryl-based material is a suitable material for the adhesive  16 .  
      In one embodiment, the films  15 ,  15   a ,  15   b  and  15   c  have a width of between about 2 and 15 cm. When the width of the films is less than 2 cm, the area thereof is too small compared to the entire area of the positive and the negative electrodes  11  and  12  to provide the desired rigidity of the positive and the negative electrodes  11  and  12  during the winding of the positive and the negative electrodes  11  and  12 . When the film width exceeds 15 cm, the film area is so large compared to the entire area of the positive and the negative electrodes  11  and  12  that the resulting reduction in the area of the active material regions  11   c  and  12   c  at the positive and the negative electrodes  11  and  12  reduces the capacity of the electrode assembly  10  as well as the secondary battery.  
      When films such as the films  15 ,  15   a ,  15   b  or  15   c  are provided at the positive and the negative electrodes  11  and  12  as the rigidity reinforcing members, with the winding of the positive and the negative electrodes  11  and  12  around the core  14 , the rigidity-reinforced leading edges of the positive and the negative electrodes  11  and  12  are not crumpled so that a high quality electrode assembly  10  can be obtained.  
       FIGS. 5A  to  5 C illustrate electrodes according to a second embodiment of the present invention along with variations on the second embodiment.  
      In this embodiment, the rigidity reinforcing member is formed with films  18 ,  18   a  and  18   b  similar to those of the previous embodiments, except that the current collectors  11   b  and  12   b  include active material on both surfaces. For this embodiment, the films  18 ,  18   a  and  18   b  extend around the leading edge of each current collector  11   b  and  12   b  of the positive and the negative electrodes  11  and  12 .  
      The structure and the method of attaching the films  18 ,  18   a  and  18   b  to the positive and the negative electrodes  11  and  12  are like those for the previous embodiments. According to  FIG. 5A , the electrodes  11  and  12  include active material over the leading edge, and therefore, the film  18  is applied to the active material using an adhesive  16 . According to  FIGS. 5B and 5C , the leading edge of each electrode  11  and  12  does not include active material, and the films  18   a  and  18   b  are applied to the uncoated leading edges of the current collectors  11   b  and  12   b  using an adhesive  16 . The variation of  FIG. 5C  differs from that of  5 B in that the film  18   b  and adhesive  16  extend over a portion of the active material layers of the current collectors  11   b  and  12   b.    
       FIGS. 6A  to  6 C illustrate a secondary battery according to a third embodiment of the present invention along with variations on this third embodiment. According to this embodiment and its variations, the rigidity reinforcing member is formed by folding the leading edge of each current collector  11   b  and  12   b  upon itself.  
      In one variation on this embodiment, the width of the folded portion is between about 2 and 15 cm for the same reasons as mentioned above.  
       FIG. 6A  illustrates the variation where the leading edges  110   b  and  120   b  are folded over the active material layer  FIG. 6B  illustrates the variation where the leading edges  110   b  and  120   b  are folded over a portion of the current collectors  11   b  and  12   b  with no active material layer.  FIG. 6C  illustrates the variation where the leading edges  110   b  and  120   b  are folded over the current collectors  11   b  and  12   b  at a region with no active material layer, and an active material layer is formed on the folded edges  110   b  and  120   b.    
      In this embodiment, the leading edges of the current collectors  11   b  and  12   b  are folded such that the positive and the negative electrodes  11  and 12 partially overlap, increasing the rigidity of the positive and the negative electrodes  11  and  12 .  
       FIGS. 7A and 7B  illustrate a secondary battery according to a fourth embodiment of the present invention and a variation.  
      In this embodiment, the rigidity reinforcing member is structured such that the leading edge portions of the positive and the negative electrodes  60  and  62  are thicker than the other portions of the positive and the negative electrodes  60  and  62 .  
      According to the variation shown in  FIG. 7A , the rigidity reinforcing member of the positive and the negative electrodes  60  and  62  are structured such that the thickness t 1  of the leading edge of the current collectors  60   a  and  62   a  is larger than the thickness t 2  of the rest of the current collectors  60   a  and  62   a , thereby making the thickness of the leading edge of the positive and the negative electrodes  60  and  62  thicker than the rest of the positive and the negative electrodes  60  and  62 .  
      In one embodiment, the ratio of t 1  to t 2  is 1.8:1, and the active material layers  60   b  and  62   b  are coated uniformly on the current collectors  60   a  and  62   a  to a thickness t 3 .  
      According to the variation shown in  FIG. 7B , the positive and negative current collectors  60   a  and  62   a  have uniform thicknesses t 4  over their entire areas thereof, while the active material layers  60   b  and  62   b  coated on the current collectors  60   a  and  62   a  are partially varied in thickness.  
      That is, for this variation, the rigidity reinforcing member is structured such that the thicknesses t 5  of the portions of the active material layers  60   b  and  62   b  corresponding to the leading edges of the positive and the negative electrodes  60  and  62  are larger than the thicknesses t 6  of the other portions of the active material layers  60   b  and  62   b.    
      According to one embodiment for this variation, the ratio of t 5  to t 6  is 1.8:1. The thickness ratio may also be said to be the ratio of the amount of coating per unit area for the portions of the active material layers  60   b  and  62   b  corresponding to the leading edges of the positive and the negative electrodes  60  and  62  to the amount of coating per unit area for the portions of the active material layers  60   b  and  62   b  corresponding to other portions of the positive and the negative electrodes  60  and  62 .  
      In this embodiment, the thicknesses of the positive and the negative electrodes  60  and  62  corresponding to the leading edges of the positive and the negative electrodes  60  and  62  are larger than the thicknesses of the other portions of the positive and the negative electrodes  60  and  62 . With such a structure, when the positive and the negative electrodes  60  and  62  are wound, crumpling is avoided, resulting in a high quality electrode assembly.  
      It is explained in various embodiments above that the rigidity reinforcing member is formed at both the positive and the negative electrodes, but the inventive structure is not limited thereto. That is, the rigidity reinforcing member may be formed at only one of the positive and the negative electrodes.  
      As described above, the leading edges of the electrodes are prevented from being distorted during the process of winding the electrodes around the core due to the formation of the rigidity reinforcing member.  
      Consequently, a high quality electrode assembly is formed, and the product reliability of the secondary battery is enhanced.  
      The secondary battery according to the present invention is effectively used as the power source for driving motors in hybrid electric vehicles (HEV), electric vehicles (EA), wireless cleaners, electric bicycles, electric scooters and the like.  
      Although exemplary 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 to the embodiments without departing from the principles and spirit of the invention, the scope of which is defined in the claims and their equivalents.