Patent Publication Number: US-8986871-B2

Title: Electrode assembly and secondary battery having the same

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a divisional of U.S. patent application Ser. No. 12/166,835, filed Jul. 2, 2008, which claims priority to and the benefit of Korean Patent Application No. 10-2007-0109576, filed Oct. 30, 2007, the entire contents of all of which are herein incorporated by reference. 
    
    
     BACKGROUND 
     1. Field 
     Aspects of the present invention relate to an electrode assembly and a secondary battery having the same, and more particularly, to an electrode assembly and a secondary battery having the same, which improves efficiency and stability thereof. 
     2. Description of the Related Art 
     In recent times, various compact and handheld electronic/electrical appliances, such as cellular phones, notebook computers, camcorders, and like devices, have been widely developed and produced. The handheld electronic/electrical appliances include a battery pack installed therein to operate as a driving power source without a separate power source. The built-in battery pack includes at least one battery to output a specific level of voltage for driving the handheld electronic/electrical appliances for a specific time. 
     A secondary battery is widely used because it is rechargeable and can be manufactured in a compact size and to have high capacity in consideration of practicality and economical efficiency. Among the secondary batteries, a lithium secondary battery is widely used due to an operating voltage (i.e., 3.6V) three times higher and a higher energy density per unit weight than a nickel-cadmium (Ni—Cd) battery and a nickel-metal hydride (Ni-MH) battery, which are widely being used in the handheld electronic/electrical appliances. 
     Among the lithium secondary batteries, a lithium ion secondary battery includes a bare cell formed by accommodating an electrode assembly having a positive electrode plate, a negative electrode plate, and a separator in a can formed of aluminum or aluminum alloy, sealing the can with a cap assembly, injecting an electrolyte into the can, and sealing the can. A lithium polymer secondary battery having a polymer separator may use a pouch instead of a can because the separator serves as an electrolyte or the separator is impregnated with an electrolytic element, and thus there is less or no leakage of the electrolyte. 
     An electrode plate is generally formed by applying slurry including an electrode active material on a surface of an electrode collector formed of metal foil. An electrode assembly may include strips of a positive electrode plate, a separator, and a negative electrode plate which are sequentially wound in a jelly-roll type. 
     An electrode collector has an electrode coating portion formed by applying a slurry long enough to form one electrode, and a non-coating portion, in which an electrode active material is not applied, to which an electrode tab is welded. 
     A transient phenomenon occurs, in which the slurry is agglomerated, so that a starting region from which the application of the slurry to the electrode collector starts is a little thicker than other regions of the electrode coating portion. Further, a tailing phenomenon occurs, and thus the slurry is applied less at an ending region where the application of the slurry to the electrode collector is terminated than other regions of the electrode coating portion. 
     The starting and ending regions of the electrode coating portion may damage the separator that electrically insulates the positive electrode plate from the negative electrode plate when pressure supplied in the process of winding the electrode assembly or external pressure is applied thereto. As an internal short circuit between the positive and negative electrode plates is generated at these regions due to the damaged separator, a battery production yield may be decreased and safety concerns may arise. 
     Accordingly, in the conventional art, insulating layers were formed at the starting and ending regions of the slurry application to prevent these problems. However, in a conventional electrode assembly, since an insulating layer partially covers an electrode coating portion, a reaction area of the electrode coating portion is decreased. Thus, the capacity of the battery is reduced as much as the decreased reaction area. Further, since an insulating layer is formed in the electrode coating portion, a diameter of an electrode assembly which is wound in a jelly-roll type becomes larger. Furthermore, by a reaction of each component at a bonding portion between an electrode coating portion and an insulating layer, dissimilar metals other than cobalt may be released. 
     SUMMARY 
     Aspects of the present invention provide an electrode assembly and a secondary battery having the same, which can improve efficiency and stability thereof. 
     According to an aspect of the present invention, an electrode assembly includes: a positive electrode plate having a positive electrode collector on which a positive electrode coating portion and a positive electrode non-coating portion are formed; a negative electrode plate having a negative electrode collector on which a negative electrode coating portion and a negative electrode non-coating portion are formed; a separator disposed between the positive electrode plate and the negative electrode plate; and an insulating member disposed on one side of the positive or negative electrode non-coating portion, and formed adjacent to at least one of the ends of the positive electrode coating portion and/or at least one of the ends of the negative electrode coating portion. 
     According to an aspect of the present invention, the insulating member may be spaced 3.5 mm or less apart from the end of the positive electrode coating portion or the negative electrode coating portion. 
     According to an aspect of the present invention, the insulating member may include an adhesive layer and an insulating film adhered to one surface of the adhesive layer. 
     According to an aspect of the present invention, the adhesive layer may not contact the positive electrode coating portion or the negative electrode coating portion. 
     According to an aspect of the present invention, the positive electrode coating portion and the negative electrode coating portion may include a uniform region in which slurry for a positive or negative electrode is uniformly applied and a non-uniform region in which slurry for a positive or negative electrode is not uniformly applied. 
     According to an aspect of the present invention, the insulating film may cover the non-uniform region. 
     According to another aspect of the present invention, a secondary battery includes: an outer casing; and an electrode assembly accommodated in the outer casing. According to an aspect of the present invention, the electrode assembly includes: a positive electrode plate including a positive electrode collector on which a positive electrode coating portion and a positive electrode non-coating portion are formed; a negative electrode plate including a negative electrode collector on which a negative electrode coating portion and a negative electrode non-coating portion are formed; and an insulating member disposed at one side of the positive or negative electrode non-coating portion and formed adjacent to at least one of the ends of the positive electrode coating portion and/or at least one of the ends of the negative electrode coating portion. 
     Additional aspects and/or advantages of the invention will be set forth in part in the description which follows and, in part, will be obvious from the description, or may be learned by practice of the invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       These and/or other aspects and advantages of the invention will become apparent and more readily appreciated from the following description of the embodiments, taken in conjunction with the accompanying drawings of which: 
         FIG. 1  is an exploded perspective view of an electrode assembly according to an exemplary embodiment of the present invention; 
         FIGS. 2A and 2B  are plan and front views of an electrode plate according to an exemplary embodiment of the present invention, respectively; 
         FIG. 2C  is a front view of an electrode plate according to an exemplary embodiment of the present invention; 
         FIG. 3  is a perspective view of a secondary battery including an electrode assembly according to an exemplary embodiment of the present invention; and 
         FIG. 4  is a perspective view of a secondary battery including an electrode assembly according to an exemplary embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     Reference will now be made in detail to the present embodiments of the present invention, examples of which are illustrated in the accompanying drawings, wherein like reference numerals refer to the like elements throughout. The embodiments are described below in order to explain the aspects of the present invention by referring to the figures. 
       FIG. 1  is an exploded perspective view of an electrode assembly according to an exemplary embodiment of the present invention. Referring to  FIG. 1 , an electrode assembly  10  includes a first electrode plate (hereinafter, referred to as a positive electrode plate)  20 , a second electrode plate (hereinafter, referred to as a negative electrode plate)  30  and a separator  40 . 
     The electrode assembly  10  includes the positive electrode plate  20 , the negative electrode plate  30 , and the separator  40 , which are stacked and wound in a jelly-roll type electrode assembly. Although described as a jelly-role type electrode assembly, the electrode assembly  10  is not limited thereto. The separators  40  are disposed between the positive electrode plate  20  and the negative electrode plate  30  to prevent a short circuit between the electrode plates  20  and  30 . 
     The positive electrode plate  20  includes a positive electrode collector  21  to collect electrons generated by a chemical reaction and to deliver them to an external circuit, and a positive electrode coating portion  22  in which slurry for a positive electrode including a positive electrode active material is applied to one surface or both surfaces of the positive electrode collector  21 . Also, a positive electrode non-coating portion  23  is formed, in which the positive electrode collector  21  is exposed because the slurry for a positive electrode including the positive electrode active material is not applied to one surface or both surfaces at one or both ends of the positive electrode collector  21 . 
     The positive electrode collector  21  may be formed of stainless steel, nickel, aluminum, titanium or an alloy thereof, or aluminum or stainless steel whose surface is treated with carbon, nickel titanium, or silver. Among them, aluminum or an aluminum alloy is preferred; however, aspects of the present invention do not limit the material of the positive electrode collector  21 . The positive electrode collector  21  may be formed in a foil, film, sheet, punched, porous, or foam type, and the positive electrode collector  21  is generally formed to a thickness of 1 to 50 μm, and preferably 1 to 30 μm. However, aspects of the present invention do not limit the shape and thickness of the positive electrode collector  21 . 
     The positive electrode coating portion  22  may be formed of a material in which a conductive material, such as carbon black or graphite powder, and a binder to bind an active material are mixed with a positive electrode active material. The positive electrode active material may be at least one of a complex oxide and lithium. The complex oxide may be at least one selected from cobalt oxide, manganese oxide, and nickel oxide, or a combination thereof. However, aspects of the present invention do not limit the material of the positive electrode active material. A positive electrode tab  24 , which may be formed of a nickel or an aluminum foil to deliver electrons collected in the positive electrode collector  21  to the external circuit, is joined to the positive electrode non-coating portion  23 . 
     A protection member  25  may be included on the junction between the positive electrode tab  24  and the positive electrode non-coating portion  23 . The protection member  25  may be formed of a thermal-resistant polymer resin, such as polyester, to prevent a short circuit by protecting the junction. Moreover, the protection member  25  has sufficient width and length to completely surround the positive electrode tab  24  joined to the positive electrode non-coating portion  23 . 
     The positive electrode plate  20  also includes an insulating member  26 , which is adhered to the positive electrode non-coating portion  23  and formed adjacent to at least one of the ends of the positive electrode coating portion  22 . The insulating member  26  may be formed of an insulating tape, and the insulating member  26  may include an adhesive layer and an insulating film adhered to one surface thereof. However, aspects of the present invention do not limit the shape and material of the insulating member  26 . For example, the adhesive layer may be formed of an ethylene-acrylic ester copolymer, a rubber-based adhesive, or an ethylene-vinyl acetate copolymer; and, the insulating film may be formed of polypropylene, polyethylene terephthalate, or polyethylene naphthalate. 
     The negative electrode plate  30  includes a negative electrode collector  31  to collect electrons generated by a chemical reaction and to deliver them to an external circuit, and a negative electrode coating portion  32  in which slurry for a negative electrode including a negative electrode active material is applied to one surface or both surfaces of the negative electrode collector  31 . Also, a negative electrode non-coating portion  33  is formed, in which the negative electrode collector  31  is exposed because the slurry for a negative electrode including the negative electrode active material is not applied to one surface or both surfaces of one or both ends of the negative electrode collector  31 . 
     The negative electrode collector  31  may be formed of stainless steel, nickel, copper, titanium or an alloy thereof; or copper or stainless steel whose surface is treated with carbon, nickel, titanium, or silver. Among these, copper or a copper alloy is preferable. However, aspects of the present invention do not limit the material of the negative electrode collector  31 . The negative electrode collector  31  may be formed in a foil, film, sheet, or punched, porous, or foam type, and it may be generally formed to a thickness of 1 to 50 μm, and preferably 1 to 30 μm. However, aspects of the present invention do not limit the shape and thickness of the negative electrode collector  31 . 
     The negative electrode coating portion  32  may be formed of a material in which a conductive material such as carbon black and a binder to fix an active material, such as polyvinylidene fluoride (PVDF), styrene butadiene rubber (SBR), or polytetrafluoroethylene (PTFE), are mixed with a negative electrode active material. The negative electrode active material may be a carbon material, such as crystalline carbon, amorphous carbon, carbon complex or carbon fiber, or lithium metal or a lithium alloy; however, aspects of the present invention do not limit the material of the negative electrode active material. A negative electrode tab  34  formed of a nickel foil to deliver electrons collected in the negative electrode collector  31  to an external circuit is joined to the negative electrode non-coating portion  33  through a junction. 
     A protection member  35  may be disposed on the junction between the negative electrode tab  34  and the negative electrode non-coating portion  33 . The protection member  35  may be formed of a thermal-resistant polymer resin, such as polyester, to prevent a short circuit by protecting the junction. Moreover, the protection member  35  has sufficient width and length to completely surround the negative electrode tab  34  joined to the negative electrode non-coating portion  33 . 
     The negative electrode plate  30  also includes an insulating member  36  which is adhered to the negative electrode non-coating portion  33  and formed adjacent to at least one of the ends of the negative electrode coating portion  32 . The insulating member  36  may be formed of an insulating tape, and the insulating member  36  may include an adhesive layer and an insulating film adhered to one surface thereof. However, aspects of the present invention do not limit the shape and material of the insulating member  36 . For example, the adhesive layer may be formed of an ethylene-acrylic ester copolymer, a rubber-based adhesive, or an ethylene-vinyl acetate copolymer; and, the insulating film may be formed of polypropylene, polyethylene terephthalate, or polyethylene naphthalate. 
     The separator  40  is generally formed of a thermoplastic resin, such as polyethylene or polypropylene, and the surface of the separator  40  is generally porous. A through-hole in the porous surface, if present, closes when the separator  40  softens at a temperature near a melting point of the thermoplastic resin due to an increase in an inner temperature of the secondary battery. Thus, the separator  40  becomes an insulating film. Accordingly, migration of lithium ions between the positive electrode plate  20  and the negative electrode plate  30  is interrupted so that electric current does not flow from the positive electrode plate  20  to the negative electrode plate  30 ; thus, the inner temperature of the secondary battery stops increasing. 
     Further, the insulating members  26  and  36  may be formed adjacent to at least one of the ends of the positive electrode coating portion  22  and/or at least one of the ends of the negative electrode coating portion  32 , i.e., the insulating member  26  may be formed at one or both of the ends of one or each positive electrode coating portion  22  and/or the insulating member  36  may be formed at one or both of the ends of one or each negative electrode coating portion  32 . 
       FIGS. 2A and 2B  are plan and front views of an electrode plate according to an exemplary embodiment of the present invention, and  FIG. 2C  is a front view of an electrode plate according to an exemplary embodiment of the present invention. While an electrode plate, for example, a positive electrode plate  20 , will now be described with reference to  FIGS. 2A and 2C , a detailed description of a negative electrode plate  30  is generally the same as that of the positive electrode plate  20 , and thus such description will be omitted. 
     As illustrated in  FIGS. 2A to 2C , a coating portion  22  formed on one surface of a positive electrode collector  21  may be divided into non-uniform regions A and B, formed at the ends of the coating portion  22 , and a uniform region C, formed between the non-uniform regions A and B. That is, in a starting part in which an application of slurry to the positive electrode collector  21  starts, the region A is formed slightly thicker than the region C in which a positive electrode coating portion is uniformly formed because of accumulation of the slurry. Also, in an ending part where the application of the slurry to the positive electrode collector  21  is terminated, the region B is formed, in which the slurry is applied slightly thinner than the region C in which a positive electrode coating portion is uniformly formed due to a tailing phenomenon. That is, the starting part of the positive electrode coating portion is thicker than the uniform region C, and the ending part of the positive electrode coating portion is thinner than the uniform region C. 
     The positive electrode plate  20  includes an insulating member  26  adhered to a positive electrode non-coating portion  23 , adjacent to at least one of the ends of the positive electrode coating portion  22 , and formed in a stripe type to be generally parallel to the end part of the positive electrode coating portion  22 . The insulating member  26  may be formed of an insulating tape, which includes an adhesive layer  26   a  and an insulating film  26   b  adhered to one surface thereof. However, aspects of the present invention do not limit the shape and material of the insulating member  26 . For example, the adhesive layer may be formed of an ethylene-acrylic ester copolymer, a rubber-based adhesive, or an ethylene-vinyl acetate copolymer; and, the insulating film may be formed of polypropylene, polyethylene terephthalate, or polyethylene naphthalate. If the distance between the insulating member  26  and the positive electrode coating portion  22  is too great, the non-uniform regions A and B may damage the separator  40  (of  FIG. 1 ) in formation of the electrode assembly  10  (of  FIG. 1 ), and thus an internal short circuit may occur. Therefore, the distance between the insulating member  26  and the end part of the positive electrode coating portion  22  may be the same as a width of the non-uniform regions A and B, or less. Also, if the distance between the insulating member  26  and the end part of the positive electrode coating portion  22  is greater than 3.5 mm, damage to the separator  40  and internal short circuit are more likely. Accordingly, the insulating member  26  may be formed to be spaced 3.5 mm or less apart from the end part of the positive electrode coating portion  22 . 
     The insulating member  26  may be formed adjacent to at least one of the ends of the electrode coating portion  22 , i.e., the insulating member  26  may be formed at one or both of the ends of the coating portion  22  on one or both sides of the positive electrode collector  21 . 
     The thickness of the insulating member  26  is about 24 μm or more, so that the insulating member  26  can prevent damage from the non-uniform regions A and B and be capable of insulating. Also, if the insulating member  26  is thicker than the positive electrode coating portion  22 , the thickness of the electrode assembly may increase. Consequently, the thickness of the insulating member  26  may be equal to or less than the thickness of the positive electrode coating portion  22 . Further, the insulating member  26  has the same thickness as the positive electrode coating portion  22  and may have the same thickness as a protrusion of the region A at the adjoining part with the protrusion formed by accumulation of the slurry. Furthermore, the insulating member  26 , as illustrated in  FIG. 2B , may be formed not to overlap the positive electrode coating portion  22 , or an insulating film  26   b ′ of the insulating member  26  may cover the non-uniform region of the positive electrode coating portion  22  as illustrated in  FIG. 2C . Consequently, since adhesive layers  26   a  and  26   a ′ do not overlap the positive electrode coating portion  22 , release of metals other than cobalt, which is caused by reaction of each component at the adjoining part between the electrode coating portion  22  and the adhesive layers  26   a  and  26   a ′, may be prevented. 
       FIGS. 3 and 4  are exploded perspective views of a second battery including an electrode assembly according to an exemplary embodiment of the present invention. Referring to  FIG. 3 , a secondary battery  100  includes an outer casing  110 , an electrode assembly  120  which is formed in a jelly-roll type and housed in the outer casing  110 , and a cap assembly  130  connected to one end of the outer casing  110 . The outer casing  110  may be formed of a metallic material having an opening at one end and may be a terminal. The outer casing  110  may be formed by deep-drawing steel or aluminum and may have a cylinder shape, a prismatic shape, or a pillar shape having rounded corners. 
     The electrode assembly  120  includes a first electrode plate  122  connected with a first electrode tab  121 , a second electrode plate  124  connected with a second electrode tab  123 , and a separator  125 , which are wound. The separator  125  is disposed between the first and second electrode plates  122  and  124  to insulate the first and second electrode plates  122  and  124  from each other. The first and second electrode plates  122  and  124  include an insulating member, which is similar as that described in  FIGS. 1 to 2C , and thus the detailed description thereof will be omitted. 
     The cap assembly  130  includes a planar-shaped cap plate  131 , which has a size and shape corresponding to the opening of the outer casing  110 . In the cap plate  131 , a terminal through-hole  131   a  and an electrolyte injection hole  131   b  through which the electrolyte is injected are formed, and the electrolyte injection hole  131   b  is sealed by a plug  131   c  for the electrolyte injection hole  131   b.    
     An electrode terminal  132  is inserted through the terminal through-hole  131   a , and a tube-type gasket  133  is disposed around the electrode terminal  132  to electrically insulate the electrode terminal  132  from the cap plate  131 . 
     An insulting plate  134  is disposed under the cap plate  131 , and a terminal plate  135  is disposed under the insulating plate  134 . A first electrode tab  121 , which is led from and electrically connected to the first electrode plate  122 , is welded to the bottom surface of the cap plate  131 . A second electrode tab  123 , which is led from and electrically connected to the second electrode plate  124 , is welded to the bottom surface of the terminal plate  135 . Moreover, an insulating case  136  is disposed on the electrode assembly  120  accommodated in the outer casing  110  so that the electrode assembly  120  is electrically insulated from the cap assembly  130 . 
     The insulating case  136  has a through-hole  136   a  for injection of the electrolyte in a position corresponding to the electrolyte injection hole  131   b  formed in the cap plate  131 . The insulating case  136  also has a groove  136   b  and a hole  136   c  are formed to guide the first and second electrode tabs  121  and  123  through the insulating case  136  while maintaining a predetermined distance between the first and second electrode tabs  121  and  123 . 
     The secondary battery  100  formed as above may further include a printed circuit board on which a protection device is mounted to prevent safety concerns such as overcurrent, overdischarge, or overcharge. Also, to protect the exterior of the secondary battery  100 , tubing or labeling may be further performed. Alternatively, a separate outer case may surround the secondary battery  100 . 
     Referring to  FIG. 4 , a secondary battery  200  includes a pouch-type outer casing  210  including a top outer casing  211  and a bottom outer casing  212 , and an electrode assembly  220  housed in the outer casing  210 . The top and bottom outer casings  211  and  212  are joined to each other at one side, and the other sides are open to accommodate the electrode assembly  220 . While, in one of the top or bottom outer casing  211  or  212 , a space in which the electrode assembly  220  is housed may be formed; in  FIG. 4 , the space is formed in the lower outer casing  212 . Top and bottom sealing parts  211   a  and  212   a  are formed to be sealed by a method such as thermal bonding about the periphery of the top and bottom outer casings  211  and  212 . 
     The outer casing  210  may be formed in a multi-layered structure of a thermal bonding layer  210   a  having thermal bonding characteristics to serve as a sealant, a metal layer  210   b  formed of a metallic material to maintain mechanical strength and serve as a barrier to moisture and oxygen, and an insulating layer  210   c.    
     The electrode assembly  220  may include a first electrode plate  222  connected to a first electrode tab  221 , a second electrode plate  224  connected to a second electrode tab  223 , and a separator  225  interposed between the both electrode plates  222  and  224 , which are wound. The first and second electrode plates  222  and  224  have an insulating member, which is the same as that described in  FIGS. 1 to 2C , and thus the detailed description of the insulating member will be omitted. 
     Adhesive tab tapes  226  and  227  may be further disposed on overlapping parts of the sealing parts  211   a  and  212   a  and the first and second electrode tabs  221  and  223  in order to seal the case. 
     The secondary battery  200  formed as above may further include a printed circuit board on which a protection device is mounted at one side to prevent safety concerns, for example, overcurrent, overdischarge, and overcharge. To protect an exterior of the secondary battery  200 , tubing or labeling may be further applied. Alternatively, a separate outer case may surround the secondary battery  200 . 
     According to aspects of the present invention, an electrode coating portion is not in contact with an adhesive layer, so that a decrease in reaction area of the coating portion may be prevented, and a battery capacity may be increased by as much as the decreased area. Since the electrode coating portion is not covered by an insulating member, the thickness of an electrode assembly may be decreased. Thus the diameter of the electrode assembly wound as a jelly-roll type may be decreased. Moreover, aspects of the present invention may prevent release of dissimilar metals other than cobalt from an adhering part between the electrode coating portion and the insulating layer. Furthermore, aspects of the present invention may prevent damage to a separator generated due to non-uniformity of the ends of the electrode coating portion, and aspects of the present invention may prevent a short circuit between two different electrode plates so as to improve stability. 
     Although a few 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 in this embodiment without departing from the principles and spirit of the invention, the scope of which is defined in the claims and their equivalents.