Abstract:
A pouch type battery includes an electrode assembly having a first electrode, a second electrode and a separator between the first electrode and the second electrode, the first electrode, second electrode and separator being wound together, an electrolyte, a pouch accommodating the electrode assembly and the electrolyte, and a fixing member fixing a winding end of the electrode assembly. The fixing member includes a base layer and an adhesive layer located at either side of the base layer, the fixing member making contact with external surfaces of the electrode assembly, and the base layer being a material that melts and acquires adhesiveness upon contact with the electrolyte. A portion of the base layer in contact with the electrolyte is in a melted condition and is separated from the adhesive layer.

Description:
BACKGROUND 
     Korean Patent Application No. 10-2012-0011318, filed on Feb. 3, 2012, in the Korean Intellectual Property Office, and entitled: “Pouch Type Battery,” is incorporated by reference herein in its entirety. 
     1. Field 
     An embodiment relates to a pouch type battery. 
     2. Description of the Related Art 
     In a secondary battery, a separator between a positive electrode plate and a negative electrode plate (hereinafter, the positive electrode plate, the negative electrode plate and the separator are collectively referred to as an electrode assembly) may function not only as a separating insulator in a lithium ion battery but also as a medium of ion conduction, that is, an electrolyte. The separator may be made of, for example, a gel-type polymer electrolyte formed in a state in which an electrolyte is impregnated in a polymer to improve ionic conductivity. 
     Secondary batteries are manufactured in various shapes. Specifically, a pouch type battery may include the electrode assembly having the separator as an insulator disposed between the positive electrode plate and the negative electrode plate, and a thin flexible pouch that accommodates the electrode assembly. Here, the pouch may have an inner space formed by adhering its edges. 
     The pouch material may have a multilayered structure including a metal layer and insulating layers covering surfaces of the metal layer. The insulating layers may prevent the metal layer interposed between the insulating layers from being shorted to conductive materials inside or outside the pouch. 
     SUMMARY 
     According to embodiments, there is provided a pouch type battery including an electrode assembly having a first electrode, a second electrode and a separator between the first electrode and the second electrode, the first electrode, second electrode and separator being wound together, an electrolyte, a pouch accommodating the electrode assembly and the electrolyte, and a fixing member fixing a winding end of the electrode assembly. The fixing member includes a base layer and an adhesive layer located at at least one side of the base layer, the fixing member contacting external surfaces of the electrode assembly. A portion of the base layer in contact with the electrolyte is in a melted condition. The adhesive layer is separated from a corresponding region with the portion of the base layer. 
     The separated adhesive layer includes a first region and a second region separated from each other by a separation distance in a range of 0.01 mm to 0.3 mm. 
     The portion of the base layer in the melted condition may adhesively contact an interior surface of the pouch. 
     The fixing member may have a thickness in a range of 10 μm to 35 μm. 
     The adhesive layer may have a thickness of 2 to 16% of the overall thickness of the fixing member. 
     The adhesive layer may have a thickness in a range of 1 μm to 4 μm. 
     The base layer may include a material selected from polystyrene, oriented polystyrene, polyamide, polyacrylonitrile, polyvinyl alcohol, polycarbonate, and polyethylene vinylacetate. The base layer may be an oriented polystyrene (OPS) film. 
     The electrolyte may include a carbonate-based solvent. The electrolyte may include at least one selected from dimethyl carbonate (DMC), diethyl carbonate (DEC) and dipropyl carbonate (DPC). 
     The fixing member may surround the overall outermost surface of the electrode assembly. 
     The pouch may include a first pouch portion and a second pouch portion to accommodate the electrode assembly, adhering portions formed by adhering opposing edges of the first pouch portion and the second pouch portion, and a planar part connecting the opposing adhering portions. 
     The pouch may have a multilayered thin film structure including a metal layer that is a thin film, a first insulating layer covering one surface of the metal layer, and a second insulating layer covering another surface of the metal layer, opposite to the one surface of the metal layer. 
     According to an embodiment, a pouch type battery includes an electrode assembly having a first electrode, a second electrode and a separator between the first electrode and the second electrode, the first electrode, second electrode and separator being wound together, and the electrode assembly including an outermost finishing part including a winding end of the electrode assembly and an exterior surface spaced apart stepwise from the winding end, a pouch accommodating the electrode assembly, and a fixing member on the outermost finishing part and on the exterior surface between the electrode assembly and the pouch, the fixing member including a base layer and an adhesive layer, the base layer having a thickness in a range of about 10 to about 35 μm and including a material selected from selected from polystyrene, oriented polystyrene, polyamide, polyacrylonitrile, polyvinyl alcohol, polycarbonate, and polyethylene vinylacetate, and the adhesive layer having a thickness of 2 to 16% of an overall thickness of the fixing member. 
     The pouch type battery may further include an electrolyte, wherein a portion of the base layer in contact with the electrolyte may be in a melted condition and may adhesively contact with an interior side of the pouch, and the adhesive layer includes a first region on the outermost finishing part and a second region on the exterior surface, the first region and the second region being spaced apart by a separation distance in a range of 0.01 mm to 0.3 mm. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Features will become apparent to those of ordinary skill in the art by describing in detail exemplary embodiments with reference to the attached drawings in which: 
         FIG. 1  illustrates an exploded perspective view of a pouch type battery according to an embodiment; 
         FIG. 2  illustrates a perspective view of an electrode assembly shown in  FIG. 1 ; 
         FIG. 3  illustrates a cross-sectional view schematically depicting a state in which a fixing member shown in  FIG. 1  makes contact with an interior surface of a pouch after the fixing member is exposed to an electrolyte; and 
         FIG. 4  illustrates an enlarged plan view schematically depicting a state in which a fixing member shown in  FIG. 1  connects adhesive layers separated after the fixing member is exposed to an electrolyte. 
     
    
    
     DETAILED DESCRIPTION 
     Example embodiments will now be described more fully hereinafter with reference to the accompanying drawings; however, they may be embodied in different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. 
     In the drawing figures, the dimensions of layers and regions may be exaggerated for clarity of illustration. It will also be understood that when a layer or element is referred to as being “on” another layer or substrate, it can be directly on the other layer or substrate, or intervening layers may also be present. Further, it will be understood that when a layer is referred to as being “under” another layer, it can be directly under, and one or more intervening layers may also be present. In addition, it will also be understood that when a layer is referred to as being “between” two layers, it can be the only layer between the two layers, or one or more intervening layers may also be present. Like reference numerals refer to like elements throughout. 
     Hereinafter, a pouch type battery and a manufacturing method thereof according to preferred embodiments will be described in detail with reference to the appended drawings. 
       FIG. 1  illustrates an exploded perspective view of a pouch type battery according to an embodiment and  FIG. 2  illustrates a perspective view of an electrode assembly shown in  FIG. 1 . 
     Referring to  FIGS. 1 and 2 , the pouch type battery  100  according to an embodiment includes an electrode assembly  110 , a fixing member  120  and a pouch  130 . 
     The electrode assembly  110  is manufactured such that the first electrode plate  111 , the separator  113  and the second electrode plate  112  are sequentially stacked and wound. The first electrode plate  111  may function as a positive electrode and the second electrode plate  112  may function as a negative electrode, or vice versa. In addition, the electrode assembly  110  may be accommodated in the pouch  130 . 
     The first electrode plate  111  may be formed of metal foil (e.g., aluminum foil). The first electrode plate  111  may be formed by applying a first electrode active material (e.g., a transition metal oxide) on a first electrode collector. A first electrode tab  117   a  made of aluminum may be electrically connected to an uncoated portion of the first electrode plate  111 . The first electrode tab  117   a  may protrude to one side of the pouch  130 . The first electrode tab  117   a  may have thereon an insulation tape formed at a portion of the first electrode tab  117   a . In other implementations, other materials may be used for the first electrode plate  111  and the first electrode tab  117   a.    
     The second electrode plate  112  may be formed of a metal foil (e.g., a copper or nickel foil). The second electrode plate  112  may be formed by applying a second electrode active material (e.g., graphite or carbon) on a second electrode collector. A second electrode tab  117   b  made of aluminum may be electrically connected to an uncoated portion of the second electrode plate  112 . The second electrode tab  117   b  may protrude to one side of the pouch  130 . The second electrode tab  117   b  may have thereon an insulation tape formed at a portion of the second electrode tab  117   b . In other implementations, other materials may be used for the second electrode plate  112  and the second electrode tab  117   b.    
     The separator  113  may be disposed between the first electrode plate  111  and the second electrode plate  112  to reduce the possibility of and/or prevent a short circuit, and to facilitate movement of lithium ions. The separator  113  may be formed of, for example, polypropylene, polyethylene, or a composite film of polypropylene and polyethylene. In other implementations, other materials may be used for the separator  113 . 
     The electrode assembly  110  includes an outermost finishing part  110   a  in which the winding end is positioned. The fixing member  120  may be positioned at a portion of an exterior surface  110   b  of the electrode assembly  110  and the outermost finishing part  110   a . In such a case, even if a separate tape for sealing the electrode assembly  110  is not provided, the fixing member  120  may function as a tape. As a result, the fixing member  120  may prevent the electrode assembly  110  from being loosened. 
     The fixing member  120  is positioned between the electrode assembly  110  and the pouch  130 . The fixing member  120  includes a base layer  121  having at least a portion melted when it makes contact with an electrolyte. In addition, the base layer  121  has an adhesive layer  122  formed on its rear surface. 
     Referring to  FIGS. 3 and 4 , the base layer  121  may be formed of a polymer film having at least a portion melted by making contact with electrolyte. The polymer film may be a film melted when it makes contact with the electrolyte in such a manner that at least a portion of the polymer film is melted by a carbonate solvent in the electrolyte permeating into portions between polymer molecules. For example, the polymer film may be a film formed of a material selected from polystyrene (PS), polyamide, polyacrylonitrile, polyvinyl alcohol, polycarbonate, polyethylene vinylacetate, and OPS. An oriented polystyrene (OPS) film may be used. 
     The base layer  121  may be formed to a thickness in a range of 10 to 35 μm, for example. If the thickness of the base layer  131  is less than 10 μm, the base layer  131  may be too easily melted upon exposure to the electrolyte. If the thickness of the base layer  131  is greater than 35 μm, the base layer  131  may not be melted by exposure to the electrolyte, thereby lowering the effect of suppressing deformation of the electrode assembly  110 . 
     The base layer  121  includes a first base layer  121   a  and a second base layer  121   b . The first base layer  121   a  is formed on a first region  122   a  of the adhesive layer  122  and the second base layer  121   b  is formed on a second region  122   b  of the adhesive layer  122 . The first and second base layers  121   a  and  121   b  may have adhesiveness by exposure to the electrolyte to then make contact with the interior side of the pouch. In addition, the first and second base layers  121   a  and  121   b  may be connected to each other. Accordingly, it may be possible to prevent the electrode assembly  100  from being loosened. 
     The adhesive layer  122  may include a general adhesive without limitation. For example, the adhesive layer  122  may be formed by applying an acryl-based adhesive on the base layer  121 . The acryl-based adhesive may be selected from poly methyl methacrylate (PMMA), poly ethyl methacrylate (FEMA) and poly butyl methacrylate (PBMA). 
     The adhesive layer  122  may be coated on the base layer  121  to various thicknesses using various suitable methods. The adhesive layer  122  may be formed by coating an adhesive to a thickness of 2 to 16% as the overall thickness of the fixing member by knife coating. For example, when the base layer  121  has a thickness of 25 μm, the adhesive layer  122  may be coated to a thickness of 1 to 4 μm. 
     The adhesive layer  122  has a first region  122   a  attached to a winding end of the electrode assembly  110  and a second region  122   b  attached to a portion of the exterior surface  110   b  of the electrode assembly  110 . The adhesive layer  122  may be separated from the outermost finishing part  110   a  corresponding to the winding end of the electrode assembly  110 . For example, the first region  122   a  and the second region  122   b  may be separated from each other by a separation distance A. 
     The separation distance A may be in a range of 0.01 mm to 0.3 mm. If the distance A is less than 0.01 mm, no separation may occur, that is, if the separation distance A of the adhesive layer  122  is too small, such that the adhesive layer  122  is hardly separated, the effect of suppressing deformation of the electrode assembly  100  may be lowered. In addition, if the separation distance A of the adhesive layer  122  is greater than 0.3 mm, the electrode assembly  100  may be easily loosened. 
     The pouch  130  may accommodate the electrode assembly  110  together with an electrolyte. The electrolyte may include a carbonate-based solvent. Examples of the carbonate-based solvent may include dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methylpropyl carbonate (MPC), ethylpropyl carbonate (EPC), methylethyl carbonate (MEC), ethyl carbonate (EC), propylene carbonate (PC), and butylenes carbonate (BC). Specifically, the exemplary carbonate-based solvent may include at least one of DMC, DEC and DPC. The carbonate-based solvent may easily permeate into spaces between polymer molecules spaced apart from each other of a polymer such as polystyrene. In addition, the electrolyte may be in a liquid, solid or gel phase. 
     The pouch  130  may have a multi-layered structure. The pouch  130  may include a metal thin film  130   a  and insulating layers  130   b  and  130   c  formed at respective sides of the metal thin film  130   a.    
     The metal thin film  130   a  may be made of at least one selected from steel, stainless steel, aluminum and equivalents thereof. In other implementations, other materials may be used for the metal thin film  130   a.    
     The insulating layers  130   b  and  130   c  may include a first insulating layer  130   b  and a second insulating layer  130   c . The first insulating layer  130   b  may correspond to an exterior surface of the pouch  130 . The first insulating layer  130   b  may be made of at least one selected from nylon, polyethyleneterephthalate (PET) and equivalents thereof. However, in other implementations, other materials may be used for the first insulating layer  130   b.    
     The second insulating layer  130   c  may correspond to an interior surface of the pouch  130 . The second insulating layer  130   c  may be made of at least one selected from cast polypropylene (CPP) and equivalents thereof. In other implementations, other materials may be used for the second insulating layer  130   c.    
     In addition, the pouch  130  may generally include a first pouch portion  131  and a second pouch portion  132 . The first pouch portion  131  may have a space  131   a  to accommodate the electrode assembly  110  and the second pouch portion  132  may cover the first pouch  131  having the space  131   a . In addition, the space  131   a  may be formed by a pressing process. 
     Table 1 summarizes evaluation results with respect to the effect of suppressing deformation of the electrode assembly  110 . Examples 1 to 4 were carried out with an OPS film used as the base layer while varying thicknesses of the adhesive layer. In order to evaluate the effect of suppressing deformation of the electrode assembly  110 , a PP film was used as the base layer in Comparative Example 1 and a PET film was used as the base layer in Comparative Example 2. The embodiments are related to suppression of deformation in a pouch type battery having a pouch. Therefore, the term “suppression of deformation of the electrode assembly  110 ” in the illustrated embodiments refers to suppression of deformation of a pouch type battery. In addition, in Table 1, the term “separation distance” refers to a distance between separated portions of the adhesive layer. 
     In the pouch type batteries of Examples and Comparative Examples, suppression of deformation of each electrode assembly thereof is measured under the same conditions except for the conditions listed in Table 1. In each case, a pouch battery  100  was assembled with the fixing member  120 , including the adhesive layer  122  and the base layer  121 , disposed in one piece on the exterior surface  110   b  of the electrode assembly  110  and the outermost finishing part  110   a  of the electrode assembly  110 . After the electrolyte was added to the pouch battery, the separation distance, if any, between a portion of the adhesive layer  122  on the outermost finishing part  110   a  and a portion of the adhesive layer  122  on the exterior surface  110   b  was measured and an amount of deformation, if any, to the pouch type battery was observed. 
     
       
         
               
               
               
               
               
               
             
               
               
               
               
               
               
               
             
               
               
               
               
               
               
               
             
           
               
                   
                 TABLE 1 
               
             
             
               
                   
                   
               
               
                   
                 Base layer 
                 Adhesive layer 
                 Overall 
                 Separation 
                 Suppression 
               
             
          
           
               
                   
                   
                 Thickness 
                 Thickness 
                 thickness 
                 distance 
                 of 
               
               
                   
                 Material 
                 (μm) 
                 (μm) 
                 (μm) 
                 (mm) 
                 deformation 
               
               
                   
                   
               
             
          
           
               
                 Example 1 
                 ops 
                 25 
                 4 
                 29 
                 0.02 
                 ◯ 
               
               
                 Example 2 
                 ops 
                 25 
                 3 
                 28 
                 0.05 
                 ◯ 
               
               
                 Example 3 
                 ops 
                 25 
                 2 
                 27 
                 0.1 
                 ◯ 
               
               
                 Example 4 
                 ops 
                 25 
                 1 
                 26 
                 0.2 
                 ◯ 
               
               
                 Comparative 
                 ops 
                 40 
                 13 
                 53 
                 0 
                 X 
               
               
                 Example 1 
               
               
                 Comparative 
                 ops 
                 40 
                 2 
                 42 
                 0 
                 X 
               
               
                 Example 2 
               
               
                 Comparative 
                 PP 
                 25 
                 2 
                 22 
                 0 
                 X 
               
               
                 Example 3 
               
               
                 Comparative 
                 PET 
                 25 
                 2 
                 22 
                 0 
                 X 
               
               
                 Example 4 
               
               
                   
               
             
          
         
       
     
     As confirmed from Examples 1 to 4, the separation distance of the adhesive layer was reduced as the thickness of the adhesive layer increased, which is due to an increase in the adhesiveness of the fixing member. Accordingly, it was confirmed that the effect of suppressing deformation was high in Examples 1 to 4, specifically in Example 4. 
     In addition, as confirmed from Comparative Examples 1 and 2 in which an OPS film was used as the base layer, when the thickness of the OPS film is 40 μm, the adhesive layer is not separated from the outermost finishing part  110   a  of the electrode assembly  110 . That is to say, if the OPS film of the base layer is formed to a thickness of 30 μm or greater, deformation of the electrode assembly  110  was not suppressed. 
     In Comparative Examples 3 and 4, a PP film and a PET film were used as the base layer, respectively. It was confirmed that shrinkage or melting did not occur even if the PP film and the PET film were contacted with an electrolyte, suggesting that deformation of the electrode assembly was not suppressed in Comparative Examples 3 and 4. 
     By way of summation and review, in the pouch type battery according to the embodiment, when the base layer of the fixing member adhered to an winding end of the electrode assembly makes contact with an electrolyte, a portion of the base layer is melted to separate the adhesive layer formed on one surface of the base layer from the one surface, thereby suppressing deformation of the electrode assembly. 
     Example embodiments have been disclosed herein, and although specific terms are employed, they are used and are to be interpreted in a generic and descriptive sense only and not for purpose of limitation. Accordingly, it will be understood by those of skill in the art that various changes in form and details may be made without departing from the spirit and scope as set forth in the following claims.