Abstract:
A secondary battery includes an electrode assembly having first and second electrodes and a separator, a pouch type case for receiving the electrode assembly, and a sheath for enclosing outer sides of the case. The sheath can prevent damage to the pouch in electronic devices to which the secondary battery is applicable as an inner pack type.

Description:
CROSS-REFERENCE TO RELATED APPLICATION  
       [0001]     This application claims priority to and the benefit of Korean Patent Application No. 10-2005-0035291, filed Apr. 27, 2005, the entire content of which is incorporated herein by reference.  
       BACKGROUND OF THE INVENTION  
       [0002]     1. Field of the Invention  
         [0003]     The present invention relates to a secondary battery, and more particularly to a pouch type lithium secondary battery which has an electrode assembly received in a pouch.  
         [0004]     2. Description of the Prior Art  
         [0005]     Secondary batteries use a non-aqueous electrolyte because of the reactivity between lithium and water. The non-aqueous electrolyte may be a solid polymer containing lithium salts, or liquid in which lithium salts are dissociated from organic solvent.  
         [0006]     The secondary batteries can be classified, according to the kind of electrolyte, into a lithium metal battery and a lithium ion battery which use a liquid electrolyte, and a lithium ion polymer battery using polymer solid electrolyte.  
         [0007]     In complete solid type lithium ion polymer batteries, there is no problem of leakage of the organic electrolyte. In gel type lithium ion polymer batteries containing organic electrolyte, the leakage of the electrolyte also can be easily prevented in comparison with lithium ion batteries using liquid electrolyte. For example, the lithium ion polymer battery may use a pouch as a case for an electrode assembly, instead of a metal can.  
         [0008]     The pouch is made of multi-layer film generally having a metal foil layer and a synthetic resin layer covering the metal foil layer. The pouch makes it possible to remarkably reduce the weight of the battery, in comparison to when the metal can is used as the case for the electrode assembly. In the multilayer pouch, the foil is generally made of an aluminum material. The polymer layer forming an inner layer of the pouch protects the metal foil from the electrolyte, and prevents an electric short-circuiting between anode and cathode, and electrode tabs.  
         [0009]     In order to form a pouch type lithium secondary battery, first, an anode plate, a separator, and a cathode plate are sequentially stacked and then rolled so as to form an electrode assembly. Next, the electrode assembly is disposed in a fitted pouch. Then, upper and lower pouch films are heated and fusion-welded at open edge of the pouch so as to seal the pouch, thereby forming the pouch type bare cell battery.  
         [0010]     Such a bare cell battery may form an inner pack type battery. The inner pack type battery refers to a battery like a bare cell battery which is directly inserted into the body of an electronic device such as a digital camera or a digital camcorder requiring the secondary battery and which is then covered with a cover member forming an exterior surface of the electronic device. The inner pack type battery has an excellent merit of enduring exterior impact.  
         [0011]     Specifically, elements or structure, such as a protection circuit module connected to the electrodes of the bare cell battery, or a positive temperature coefficient element, is mounted in the body of the electronic device.  
         [0012]     Therefore, in the case of the inner pack type secondary battery in which a protection circuit module, a positive temperature coefficient element, etc. are mounted in a body of an electronic device, just the protection circuit module can be replaced with a new module when a protection circuit is damaged. Therefore, the inner pack type secondary battery has an improved yield and a less chance of being exposed to exterior impact, in comparison with the secondary battery integrated with the protection circuit module.  
         [0013]     However, the conventional secondary battery where the electrode assembly is received in the soft pouch has a problem in that a soft pouch may be easily damaged during mounting of the secondary battery in the electronic device.  
       SUMMARY OF THE INVENTION  
       [0014]     Accordingly, the present invention has been made to solve the above-mentioned problems occurring in the prior art, and an object of the present invention is to provide a secondary battery which includes a sheath for enclosing the outside of a pouch, thereby preventing a soft pouch from being damaged.  
         [0015]     In order to accomplish the object of the present invention, there is provided a secondary battery which comprises: an electrode assembly comprising a first electrode plate, a second electrode plate, and a separator interposed between the first electrode plate and the second electrode plate; a pouch having a case for receiving the electrode assembly; and a sheath for enclosing the pouch. Preferably, the sheath encloses sides of the pouch in rounding.  
         [0016]     According to an aspect of the present invention, the sheath is preferably formed with material having a mechanical strength higher than that of material forming the case, in order to reinforce the strength of the case. The sheath may be made of stainless steel, so as to be formed as a foil. Furthermore, the sheath may be made of synthetic resin. In addition, the sheath has a thickness of less than 0.1 mm.  
         [0017]     According to still an aspect of the present invention, the sheath has a lower surface portion which is in contact with a lower surface of the pouch, side surface portions which are in contact with a side surface of the pouch, and upper surface portions which are in contact with an upper surface. Further, the side surface portions of the sheath are formed at both edges of the lower surface portion of the sheath, and the upper surface portions of the sheath are connected to the side surface portions around the lower surface portion of the sheath. Further, the lower surface portion of the sheath has an area corresponding to that of the lower surface of the pouch, and the side surface portions of the sheath have an area corresponding to that of the side surface of the pouch.  
         [0018]     According to yet an aspect of the present invention, the sheath includes a lower surface portion which is in contact with a lower surface of the pouch, side surface portions which are in contact with side surfaces of the pouch, respectively, upper surface portions which are in contact with an upper surface of the pouch, and a rear surface portion which is in contact with a rear surface of the pouch. Here, the rear surface portion of the sheath has an area corresponding to a rear surface of the pouch, and is integrated with the lower surface portion of the sheath.  
         [0019]     According to still yet an aspect of the present invention, the sheath includes a first side sheath and a second side sheath which cover both sides of the pouch respectively. Here, the left side sheath and the right side sheath respectively have a lower surface portion which is in contact with a lower surface of the pouch, a side surface portion which is in contact with a side surface of the pouch, and an upper surface portion which is in contact with an upper surface of the pouch, the lower surface portion and the upper surface portion of each of the left side sheath and the right side sheath have areas corresponding to half areas of the lower surface and the upper surface of the pouch respectively. Furthermore, each of the left side sheath and the right side sheath further has a rear surface portion which is in contact with the rear portion of the pouch. Each of the left side sheath and the right side sheath are integrally formed by molding.  
         [0020]     According to a further aspect of the present invention, the sheath includes an upper sheath and a lower sheath which are coupled to each other to cover an upper portion and a lower portion of the pouch. Here, the upper sheath has an upper surface portion which is in contact with an upper surface of the pouch and side surface portions which are formed at both edges of the upper surface thereof so as to contact side surfaces of the pouch, and the lower sheath has a lower surface portion which is in contact with a lower surface of the pouch and side surfaces of the pouch which are formed at both edges of the lower surface thereof so as to contact of a lower surface of the pouch. The upper sheath and the lower sheath further have a rear surface portion which is in contact with a rear surface of the pouch respectively. Further, each of the upper and lower sheaths is integrally formed by molding.  
         [0021]     According to another aspect of the present invention, the sheath has information including either a serial number of the secondary battery or the manufacturer, which is printed on an exterior surface thereof.  
         [0022]     According to yet an aspect of the present invention, the secondary battery is an inner pack battery.  
         [0023]     According to still another aspect of the present invention, a secondary battery includes: an electrode assembly comprising a first electrode plate having a first electrode tab, a second electrode plate having a second electrode tab, and a separator interposed between the first electrode plate and the second electrode plate; a pouch having a case receiving the electrode assembly; and a sheath covering at least sides of the pouch. The sheath may further enclose a rear surface of the pouch which is opposite to a front surface from which the first and second electrode tabs extend. The sheath may be a single sheath which is rolled over the pouch or composed of a first sheath and a second sheath each which cover a half of the pouch to cover the pouch. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0024]     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:  
         [0025]      FIG. 1  is an exploded perspective view showing a secondary battery having an electrode assembly and a pouch;  
         [0026]      FIG. 2A  is a plan view showing a sheath for a pouch according to an embodiment of the present invention;  
         [0027]      FIG. 2B  is a perspective view showing the sheath and the pouch of  FIG. 2A ;  
         [0028]      FIG. 3  is a plan view showing a sheath according to another embodiment of the present invention;  
         [0029]      FIG. 4  is a perspective view showing a sheath according to still another embodiment of the present invention;  
         [0030]      FIG. 5  is a perspective view showing a sheath according to yet another embodiment of the present invention; and  
         [0031]      FIG. 6  is an exploded perspective view showing an electronic device to which a secondary battery according to the present invention is applied. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0032]     Hereinafter, a secondary battery according to the present invention will be described with reference to the accompanying drawings.  
         [0033]      FIG. 1  is an exploded perspective view showing a secondary battery having an electrode assembly and a pouch.  FIG. 2A  is a plan view showing a sheath for a pouch according to an embodiment of the present invention.  FIG. 2B  is a perspective view showing the sheath and the pouch of  FIG. 2A .  FIG. 6  is an exploded perspective view showing an electronic device to which a secondary battery according to the present invention is applied.  
         [0034]     Referring to  FIGS. 1, 2A  and  2 B, the lithium secondary battery  100  according to the embodiment of the present invention includes an electrode assembly  110 , a pouch  200  having a case  120  in which the electrode assembly  110  is received, and a sheath  210  for enclosing the pouch  200 .  
         [0035]     The electrode assembly  110  includes first and second electrode plates  111  and  115  coated with first and second active material layers (not shown), and a separator  113  interposed between the first and second electrode plates  111  and  115  so as to prevent an electric short-circuiting between the first and second electrode plates  111  and  115  as well as to allow only the movement of lithium ions. The electrode assembly  110  is rolled several times. The first and second electrode plates  111  and  115  have first and second electrode tabs  111   a  and  115   a  coupled thereto, respectively. The first electrode plate  111  may form an anode plate, and the second electrode plate  115  form a cathode plate. In this case, the anode plate  111  is made of an aluminum material, and the cathode plate  115  is made of an copper material. On the other hand, the separator  113  is generally made of polyethylene resin or polypropylene resin. However, the present invention does not limit the material of these elements to those mentioned above.  
         [0036]     Chalcogenide compounds, for example composite metal oxides such as LiCoO 2 , LiMn 2 O 4 , LiNiO 2 , LiNiO 2 , LiNi (1-x) Co x O 2  (0&lt;x&lt;1), and LiMnO 2 , are used as the anode active material. Carbon-based materials, Si, Sn, Tin oxide, composite tin alloys, transition metal oxide, and lithium metal oxide, etc. are used as the cathode active material.  
         [0037]     The case  120  includes a first region  121  having a recess  121   a  with a predetermined depth in order to receive the electrode assembly  110  and a flange member  121   b , and a second region  122  with an area enough to cover the recess  121   a  of the first region  121 . The case  120  is made of a pouch film in which an adhesive layer is coated on one surface of an aluminum foil and an insulation layer is coated on the other surface of the aluminum foil. The adhesive layer is formed with denaturalized polypropylene resin such as casted polypropylene (CPP) resin, and the insulation layer is made of synthetic resin such as nylon or polyethyleneterephtalate (PET). However, the present invention does not limit the material of the case  120  to those mentioned above.  
         [0038]     Further, the recess  121   a  of the pouch is formed with a predetermined depth, while the first and second electrode tabs  111   a  and  115   a  connected to the electrode assembly  110  extend at a desired distance outward from an edge of the case  120 , i.e. the flange member  121   b.    
         [0039]     The sheath  210  has a lower surface portion  211  that is in contact with a lower surface  201  of the pouch  200 , side surface portions  212  that is in contact with side surfaces  202  of the pouch  200  respectively, and an upper surface portion  213  that is in contact with an upper surface  203  of the pouch  200 . The sheath  210  is formed in such a manner that both side surface portions  212  are connected to both edges of the lower surface  211  respectively, and the upper surface portions  213  are respectively formed at a side of each of the side surface portions  212  around the lower surface portion  211 . The lower surface portion  211  has an area corresponding to that of the lower surface of the pouch  200 , while the side surface portions  212  have an area corresponding to that of the side surface of the pouch  200 . Further, the upper surface portions  213  formed at both edges of the lower surface portion  211  have a total area corresponding to an area of the upper surface of the pouch  200 . In addition, the sheath  210  encloses the sides of the case  120  from the lower surface to the side surfaces of the case  120  in rounding. Specifically, the sheath  210  of the case  120  makes the case  120  have rounded sides, so as to reduce the contact area of the case with the electronic device, thereby facilitating insertion and separation of the case  120  in and from the electronic devices when the case  120  is inserted into and separated from the electronic devices.  
         [0040]     The sheath  210  is adhered to the case  120  by a separate adhesive so as to completely enclose the exterior surface of the case  120 , thereby reinforcing the strength of the pouch  200 . Therefore, the sheath  210  is made of a material having a mechanical strength higher than that of material for the case  120 , for example stainless steel or synthetic resin. Further, the sheath  210  is preferably formed as a foil. Furthermore, the sheath  210  is preferably formed with a thickness of less than 0.1 mm. When the sheath  210  has a thickness of more than 0.1 mm, the pouch has a reduced inner volume due to the thickness increase of the sheath  210  within the predetermined entire volume, so that the capacity of the secondary battery is remarkably reduced.  
         [0041]     On the other hand, the sheath  210  may have information relating to one of a serial number, manufacturing data, and manufacturer of the secondary battery, printed on the exterior surface thereof.  
         [0042]     The first and second electrode tabs  111   a  and  115   a  extending outward from the case  120  protrude outward from the sheath  210 . The first and second electrode tabs  111   a  and  115   a  which protrude outward are connected to a protection circuit board (not shown) which is mounted outside of the secondary battery, i.e. in the electronic device.  
         [0043]     The electronic device may be a portable mobile phone  300 .  
         [0044]     The portable mobile phone  300  is provided at a side thereof with a battery mounting portion  310  having a desired space in which the secondary battery is inserted, and a cover  320  for covering the exterior surface of the battery mounting portion  210 . The cover  320  has a fixing button  321  installed thereto so as to fix the cover  320  to the portable mobile phone  300 . The portable mobile phone  300  is provided with the protection circuit board, which is connected to the first and second electrode tabs  111   a  and  115   a  of the secondary battery  100 , mounted around the battery mounting portion  310  in the portable mobile phone  300 .  
         [0045]     Hereinafter, the sheath according to another embodiment of the present invention will be described.  
         [0046]      FIG. 3  is a plan view showing the sheath according to another embodiment of the present invention. The same reference numerals are used to denote the same part of the sheath  210   a  of the present embodiment as that of the sheath  210  according to the embodiment of  FIG. 2A , and the description relating to the same parts will be omitted.  
         [0047]     Referring to  FIG. 3 , the sheath  210   a  according to another embodiment of the present invention has a lower surface portion  211 , side surface portions  212 , upper surface portions  213 , and a rear surface portion  214 . The rear surface portion of the sheath  210   a  may be formed at an edge of the lower surface portion  211  so as to extend perpendicular to the side surface portions  212 . The rear surface portion  214  has an area corresponding to the rear surface of the pouch  200  which is opposite to a front surface through which the first and second electrode tabs  111   a  and  115   a  extends outward, and comes into complete contact with the rear surface of the pouch  200 , so as to reinforce the strength of the rear surface of the pouch  200 . The rear surface portion  214  is integrated with the lower surface portion  211  of the sheath  210   a , or formed separately from the lower surface portion  211  and attached to the lower surface portion  211  of the sheath  210   a.    
         [0048]     Hereinafter, the sheath according to another embodiment of the present invention will be described.  
         [0049]      FIG. 4  is a perspective view showing the sheath according to another embodiment of the present invention. The same reference numerals are used to denote the same part of the sheath of the present embodiment as that of the sheath according to the embodiment of  FIG. 2A , and the description relating to the same parts will be omitted.  
         [0050]     Referring to  FIG. 4 , the sheath  210   b  includes a left side sheath  216   a  and a right side sheath  216   b , which are assembled with each other at both sides of the pouch  200  and reinforce the strength of the pouch  200 . Therefore, the left side sheath  216   a  and the right side sheath  216   b  have open sides which are opened to opposite sides of the pouch, respectively. The left side sheath  216   a  and the right side sheath  216   b  respectively have a lower surface portion  211   b  and  211   b ′, a side surface portion  212   b  and  212   b ′, and an upper surface portion  213   b  and  213   b ′. The lower surface portion  211   b  and  211   b  ′ and the upper surface portion  213   b  and  213   b  ′ respectively have an area corresponding to a half area of an upper surface or a lower surface of the pouch  200 . Further, each of the side surface portions  212   b  and  212   b  ′ of the left side sheath  216   a  and the right side sheath  216   b  has an area corresponding to a side surface of the pouch  200 . Further, each of the left side sheath  216   a  and the right side sheath  216   b  further has a rear surface portion  214   b  and  214   b  ′ formed with an area corresponding to a half area of the rear surface of the pouch  200 . Preferably, each of the left side sheath  216   a  and the right side sheath  216   b  forming the sheath  210   b  may be integrally formed by molding. The left side sheath  216   a  and the right side sheath  216   b  respectively cover the pouch  200  and adhere to the pouch  200  by a separate adhesive.  
         [0051]     Hereinafter, a sheath according to another embodiment of the present invention will be described.  
         [0052]      FIG. 5  is a perspective view showing the sheath according to another embodiment of the present invention. The same reference numerals are used to denote the same part of the sheath of the present embodiment as that of the sheath according to the embodiment of  FIG. 2A , and the description relating to the same parts will be omitted.  
         [0053]     Referring to  FIG. 5 , the sheath  210   c  according to another embodiment of the present invention includes an upper sheath  217   a  and a lower sheath  217   b , which are coupled to cover the pouch  200  from sides of the pouch  200  so as to completely reinforce the strength of the pouch  200 . The coupled upper sheath  217   a  and lower sheath  217   b  make an opening that open toward the front surface of the pouch  200 . Further, the upper sheath  217   a  has an upper surface portion  213   c , and side surface portions  212   c  formed at both edges of the upper surface portion  213   c . The lower sheath  217   b  includes a lower surface portion  211   c  and side surface portions  212   c  ′ formed at both edges of the lower surface portion  211   c . The upper and lower surface portions  213   c  and  211   c  respectively have an area corresponding to that of a lower surface or an upper surface of the pouch  200 . Each of the upper sheath  217   a  and the lower sheath  217   b  further includes a rear surface portion  214   c  formed with an area corresponding to that of a rear surface of the pouch  200 . Preferably, each of the upper and lower sheaths  217   a  and  217   b  forming the sheath  210   c  may be integrally formed by molding. The upper and lower sheaths  217   a  and  217   b  are coupled to upper and lower sides of the pouch  200 , respectively, and adhere to the pouch  200  by a separate adhesive.  
         [0054]     Hereinafter, the operation of the secondary battery according to the present invention constructed as described above will be described.  
         [0055]     The electrode assembly  110  is inserted into the recess  121   a  of the pouch  200 . The pouch  200  receiving the electrode assembly  110  is enclosed with the sheath  210 , of which both sides are rounded. The first and second electrode tabs  111   a  and  115   a  are protruded from a front side of the sheath  210  and electrically connected to the protection circuit board, so as to form the secondary battery.  
         [0056]     Since the sheath  210  enclosing the exterior surface of the case  120  has sides formed in rounding, the pouch  200  makes a smooth contact with the contact surface of the battery mounting portion  310  when the secondary battery  100  is mounted in the battery mounting portion  310 . Further, the contact surface between the sides of the pouch  200  and the inner surface of the battery mounting portion  310  is reduced to make it possible to facilitate attachment and detachment of the secondary battery  100 . Furthermore, the sheath  210  made of stainless steel or synthetic resin, etc. encloses the exterior surface of the case  120 , thereby preventing damage to the soft case  120 . Here, the secondary battery  100  is mounted in a portable mobile phone so that the first and second electrode tabs  111   a  and  115   a  are connected to the protection circuit board mounted adjacent to the battery mounting portion  310 .  
         [0057]     When the secondary battery  100  is mounted in the battery mounting portion  310  of the portable mobile phone  300 , the cover  320  is fixed to the portable mobile phone  300  by the fixing button  321 , so as to cover the battery mounting portion  310 .  
         [0058]     Although a preferred embodiment of the present invention has been described for illustrative purposes, those skilled in the art will appreciate that various modifications, additions and substitutions are possible, without departing from the scope and spirit of the invention as disclosed in the accompanying claims.