Patent Publication Number: US-2023150176-A1

Title: Pouch, Apparatus For Molding The Pouch, And Method For Manufacturing Secondary Battery Comprising The Pouch

Description:
TECHNICAL FIELD 
     The present application claims the benefit of the priority of Korean Patent Application No. 10-2020-0078759, filed on Jun. 26, 2020, which is hereby incorporated by reference in its entirety. 
     The present invention relates to a pouch of a secondary battery, an apparatus for molding the pouch, and a method for manufacturing the secondary battery comprising the pouch, and more particularly, to a molding apparatus for molding a pouch that is capable of mounting an electrode having a thicker thickness by molding a sidewall within a moldable range of a pouch sheet, a pouch manufactured using the molding apparatus, and a method for manufacturing a secondary battery comprising the pouch. 
     BACKGROUND ART 
     The demands for high-efficiency secondary batteries are rapidly increasing in the mobile device and electric vehicle fields. Among such the secondary batteries, a lithium secondary battery having high energy density, maintaining a relatively high voltage, and having a low self-discharge rate is commercially widely used, and research and development for improving performance thereof is actively being conducted. 
     The secondary battery has a structure in which an electrode assembly and an electrolyte are embedded in a case such as a can or a pouch. The electrode assembly has a structure in which positive electrodes, separators, and negative electrodes are repeatedly stacked. In general, the electrode assembly may be classified into a winding type electrode assembly in which the positive electrodes, the separators, and the negative electrodes, which are in the stacked state, are rolled to be embedded in the case and a stack type (stacked) electrode assembly in which the positive electrodes, the separators, and the negative electrodes, each of which is cut to a predetermined size, are stacked. 
     Since the winding type electrode assembly has a spirally wound structure, the winding type electrode assembly is suitable for being mounted on a cylindrical battery, but is disadvantageous in space utilization for a prismatic or pouch type battery. On the other hand, since the stack type electrode assembly is adjusted in size when the electrode and the separator are cut, the prismatic shape fitted with the case is easily obtained, but a manufacturing process is relatively complicated, and the stack type electrode assembly is relatively vulnerable to an external impact. Also, a stack &amp; folding method has been developed to combine the advantages of the winding type and the stack type. In the stack &amp; folding method, a C-type bicell (a bicell having a stack structure of a positive electrode/separator/negative electrode/separator/positive electrode) and an A-type bicell (a bicell having a stack structure of a negative electrode/separator/positive electrode/separator/negative electrode) are placed on a folding separator to fold the bicells, thereby manufacturing the electrode assembly. 
     Also, the electrode assembly manufactured in various manners as described above is mounted in a case such as a can or a pouch. 
     Among them, the pouch is manufactured by stacking a metal layer made of an aluminum material and a resin layer made of a polymer material, but when the pouch is provided in the form of a sheet, the pouch may be processed to have a fixed shape through the molding apparatus. 
     That is, referring to  FIG.  1     a,  which illustrates a state in which an electrode assembly is mounted in the pouch according to the related art, and  FIG.  1     b,  which illustrates a cross-sectional view of a state in which the pouch according to the related art is unfolded or closed, a pouch  2  on which an electrode assembly  1  having a hexahedral shape is mounted comprises a second seating part  4  on which a bottom surface of the electrode assembly  1  is seated and a first seating part  3  that covers a top surface of the electrode assembly  1 . When the electrode assembly  1  is mounted in an opened state, the first seating part  3  and the second seating part  4  are folded to cover the top and bottom surfaces of the electrode assembly  1  and then is in a closed state. 
     In the closed state, sealing portions  3   b  and  4   b  of the first seating part  3  and the second seating part  4  are in contact with each other, and in the state in which the first seating part  3  and the second seating part  4  are in contact with each other, heat and a pressure are applied to seal the pouch  2 . Here, each of grooves  3   a  and  4   a  of the first seating part  3  and the fourth seating part  4  may be provided to have a depth at which the electrode assembly  1  is capable of mounted. 
     Also, the pouch having the above-described structure is manufactured by processing a flat pouch sheet. That is, referring to  FIG.  1   c    illustrating a cross-sectional view of an apparatus for molding the pouch according to the related art, the apparatus for molding the pouch according to the related art comprises an upper mold  7  and a lower mold  6 . The lower mold  6  has a structure in which two grooves  6   a  and  6   b  are formed in both sides thereof, and a protrusion  6   c  is disposed between the two grooves  6   a  and  6   b  so as to partition the two grooves  6   a  and  6   b  from each other. 
     Also, the upper mold  7  that ascends and descends above the lower mold  6  has two cores  7  that are respectively inserted into the grooves  6   a  and  6   b  of the lower mold  6  and has a shape in which a hole  7   a  is formed so that the protrusion  6   c  of the lower mold  6  is capable of being inserted between the cores  7 . 
     Thus, in the state in which the pouch sheet is seated on the lower mold  6 , when the upper mold  7  descends to press the pouch sheet, the pouch sheet is molded to the pouch  2  having the shape of  FIG.  1   b    according to shapes of the grooves  6   a  and  6   b  and the protrusion  6   c.    
     The pouch  2  may be folded at a middle point thereof along a bending point C to accommodate the electrode assembly  1  therein. The bending point C is a folded portion  5  in  FIG.  1     a.    
     Thus, as described above, the pouch  2  has a structure in which a metal layer and a resin layer are stacked. Thus, when the molding is performed between the upper mold  7  and the lower mold  6 , there is a limit to elongation of the metal layer. As a result, since the portion d at which the elongation is performed does not increase in size, a distance t between the groove  3   a  of the first seating part and the sealing portion  3   b  and a distance between the groove  4   a  of the second seating part and the sealing portion  4   b  are inevitably limited. 
     Therefore, a thickness of the electrode assembly  1  mounted on the pouch is also limited due to the molding conditions of the pouch. Due to these constraints, the pouch type secondary battery having a larger capacity has been provided in the form that increases in area without increasing in thickness of the electrode assembly. 
     However, as the need for the high-capacity secondary battery gradually increases, the pouch capable of mounting the electrode assembly having a thicker thickness and the molding apparatus capable of manufacturing the pouch have been required. 
     DISCLOSURE OF THE INVENTION 
     Technical Problem 
     A main object of the present invention is to provide a pouch capable of mounting an electrode assembly having a thicker thickness in consideration of gradually increasing demands of a high-capacity secondary battery, a molding apparatus capable of manufacturing the pouch, and a method for manufacturing a secondary battery comprising the pouch. 
     Technical Solution 
     The present invention for achieving the above-described object provides a pouch, a molding apparatus for manufacturing the pouch, and a method for manufacturing a secondary battery comprising the pouch. 
     An apparatus for molding a pouch, which comprises a first seating part and a second seating part, which are connected to each other, wherein when an electrode assembly is mounted, the first seating part and the second seating part are folded to cover top and bottom surfaces of the electrode assembly, thereby manufacturing the pouch that is sealed in a state in which the first seating part and the second seating part are in contact with each other, according to the present invention comprises: a lower mold in which a first groove recessed by a predetermined depth from a top surface thereof is formed, and a second groove is additionally recessed from a bottom surface of the first grove; and an upper mold on which a flat portion is formed on one surface thereof, which is inserted into the first groove, and a protrusion inserted into the second groove protrudes from the flat portion, wherein, when the upper mold and the lower mold are pressed in a state in which the pouch sheet is placed between the upper mold and the lower mold, the pouch sheet is molded so that each of the first seating part and the second seating part are molded at a portion of the pouch sheet, which is pressed by the flat portion, and a sidewall configured to connect the first seating part to the second seating part and form a surface parallel to a side surface of the electrode assembly when the electrode assembly is mounted is formed. 
     The pouch may be formed by stacking a metal layer made of an aluminum material and a resin layer made of a polymer material, and a height of the protrusion protruding from the flat portion may be determined according to an elongation rate of the metal layer. 
     The second groove may be disposed at a center of the first groove, and the protrusion may be disposed at a center of the flat portion. 
     Each of an edge portion of the upper mold, which is inserted into the first groove, and an edge portion of the protrusion may be rounded at a predetermined curvature. 
     Furthermore, a pouch which comprises a first seating part and a second seating part, which are connected to each other, wherein when an electrode assembly is mounted, the first seating part and the second seating part are folded to cover top and bottom surfaces of the electrode assembly, thereby manufacturing the pouch that is sealed in a state in which the first seating part and the second seating part are in contact with each other, according to the present invention comprises: the first seating part configured to cover one of upper and lower portions of the electrode assembly; the second seating part configured to cover the other one of the upper and lower portions of the electrode assembly and have one side connected to one side of the first seating part; and a sidewall having one side connected to one side of the first seating part and the other side connected to the second seating part, wherein the sidewall is folded at each of the first seating part and the second seating part and is formed in a flat planar shape on each of both inner and outer surfaces of the pouch. The sidewall may be folded to be perpendicular to the first seating part and the second seating part. 
     Each of the first seating part and the second seating part may be formed by allowing a sealing portion to extend from each of remaining sides except for a side connected to the sidewall, and when the electrode assembly is mounted to be folded, the sealing portion of the first seating part and the sealing portion of the second seating part may be sealed. 
     When the first seating part and the second seating part are folded to be parallel to each other, an extending length of each of the sealing portion of the first seating part and the sealing portion of the second seating part, which respectively extend from the first seating part and the second seating part, may be determined according to a length of the sidewall so that the sealing portion of the first seating part and the sealing portion of the second seating part are sealed. 
     A stepped portion having a concavely recessed shape may be formed in each of an edge configured to connect the first seating part to the sidewall and an edge configured to connect the second seating part to the sidewall. 
     Furthermore, the present invention may additionally provide a method for manufacturing a secondary battery comprising a pouch having the above-described configuration. 
     A method for manufacturing a secondary battery comprising a pouch, which comprises a first seating part and a second seating part, which are connected to each other, wherein when an electrode assembly is mounted, the first seating part and the second seating part are folded to cover top and bottom surfaces of the electrode assembly, thereby manufacturing the pouch that is sealed in a state in which the first seating part and the second seating part are in contact with each other, and an electrode assembly, which is embedded together with an electrolyte in the pouch, according to the present invention comprises: a pouch molding step (S 10 ) of molding the pouch; and a sealing step (S 20 ) of embedding the electrode assembly and the electrolyte in the molded pouch to seal a sealing portion of the pouch, wherein the pouch molding step (S 10 ) comprises: a step (S 11 ) of seating a pouch sheet on a lower mold in which a first groove recessed by a predetermined depth from a top surface thereof, and a second groove is additionally recessed from a bottom surface of the first groove; a step (S 12 ) of pressing the pouch sheet to mold the pouch by using an upper mold on which a flat portion is formed on one surface thereof, which is inserted into the first groove, and a protrusion inserted into the second groove protrudes from the flat portion; and a step (S 13 ) of folding a pouch sheet that is molded to form first and second seating parts, which face each other, and a sidewall connecting the first seating part to the second seating part. 
     The sidewall may be molded so that each of both inner and outer surfaces thereof has a flat planer shape. 
     In the step (S 13 ) of folding the molded pouch sheet, the sidewall may be folded to be perpendicular to the first seating part and the second seating part. 
     Advantageous Effects 
     In the pouch having the above-described configuration according to the present invention, the planar sidewall connecting the first seating part to the second seating part may be formed to mount the electrode assembly having the thicker thickness by adjusting the length of the sidewall. 
     That is, although the elongation of the metal layer is limited in the pouch according to the related art to limit the thickness of the mountable electrode assembly, since the sidewall in the pouch according to this specification has the flat surface that is not elongated between the upper mold and the lower mold, the length of the flat surface may be adjusted to mount the electrode assembly having the thicker thickness. 
     In addition, the edge portions of the upper mold and the lower mold may be rounded to reduce the deformation due to the pouch sheet to be stabbed and pressed. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1   a    is a perspective view illustrating a state in which an electrode assembly is mounted in a pouch according to a related art. 
         FIG.  1   b    is a cross-sectional view illustrating an unfolded state and a closed state (folded state) of the pouch according to the related art. 
         FIG.  1   c    is a cross-sectional view of an apparatus for molding the pouch according to the related art. 
         FIG.  2    is a cross-sectional view of an apparatus for molding a pouch according to an embodiment of the present invention. 
         FIG.  3    is a cross-sectional view illustrating a state in which an electrode assembly is mounted in the pouch manufactured using the apparatus for molding the pouch of  FIG.  2   . 
         FIG.  4    is a cross-sectional view illustrating a state in which the electrode assembly is mounted in the pouch according to the related art and a cross-sectional view illustrating a state in which the electrode assembly having a thicker thickness is mounted in the pouch according to the present invention. 
     
    
    
     MODE FOR CARRYING OUT THE INVENTION 
     Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings in such a manner that the technical idea of the present invention may easily be carried out by a person with ordinary skill in the art to which the invention pertains. The present invention may, however, be embodied in different forms and should not be construed as limited to the embodiments set forth herein. 
     In order to clearly describe the present invention, parts irrelevant to the description are omitted, and the same reference numerals are assigned to the same or similar components throughout the specification. 
     Also, terms or words used in this specification and claims should not be restrictively interpreted as ordinary meanings or dictionary-based meanings, but should be interpreted as meanings and concepts conforming to the scope of the present invention on the basis of the principle that an inventor can properly define the concept of a term to describe and explain his or her invention in the best ways. 
     The present invention provides a pouch, a molding apparatus capable of manufacturing the pouch, and a method for manufacturing a secondary battery comprising the pouch. Hereinafter, preferred embodiments of the present invention will be described in more detail with reference to the accompanying drawings. 
     First Embodiment 
     The present invention provides an apparatus for molding a pouch as a first embodiment. An apparatus for molding a pouch according to the present invention comprises a first seating part  11  and a second seating part  12 , which are connected to each other. When an electrode assembly  1  is mounted, the first seating part  11  and the second seating part  12  are respectively folded to cover top and bottom surfaces of the electrode assembly  1  to manufacture a pouch  10  that is sealed in a state in which sealing portions  11   a  and  12   a  of the first seating part  11  and the second seating part  12  are in contact with each other. 
       FIG.  2    is a cross-sectional view of the apparatus for molding the pouch according to an embodiment of the present invention. As illustrated in  FIG.  2   , the molding apparatus according to this specification comprises a lower mold  20  and an upper mold  30 . 
     The lower mold  20  has a flat bottom surface. Here, a first groove  21  is formed at a predetermined depth in the top surface, and a second groove  22  is formed in a bottom surface of the first groove  21 . 
     The first seating part  11  of the pouch  10  is mold at one side of the first groove  21  based on the second groove  22 , and the second seating part  12  is molded at the other side of the first groove  21  based on the second groove  22 . Also, the sidewall  13  of the pouch  10  is formed on a portion at which the second groove  22  is disposed. Thus, an area of the first groove  21  is determined according to sizes (areas) of the first seating part  11  and the second seating part  12  of the pouch  10  to be manufactured. Likewise, an area of the second groove  22  is determined according to a size of the sidewall  13  connecting the first seating part  11  to the second seating part  12 . 
     However, a depth of the first groove  21  and a depth of the second groove  22  may be determined according to an elongation rate of a metal layer provided in the pouch  10 . That is, since a pouch sheet molded as the pouch  10  is provided by stacking a metal layer made of an aluminum material and a resin layer made of a polymer material. Thus, in order to prevent the metal layer from being damaged, the depths (a height at which the flat portion is inserted and a height at which a protrusion protrudes from the flat portion) are determined according to the elongation rate of the metal layer. 
     Furthermore, the upper mold  30  has a structure in which the flat portion  31  is formed on one surface that is inserted into the first groove  21  of the lower mold  20 , and the protrusion  32  inserted into the second groove  22  additionally protrudes from the flat portion  31 . In  FIG.  2   , although only the flat portion  31  and the protrusion  32  inserted into the first groove  21  and the second groove  22  are illustrated, the flat portion  31  and the protrusion  32  may be integrally formed. Here, a sliding device that is elevatably connected and a portion (not shown) configured to press the sealing portions  11   a  and  12   a  of the pouch may be further provided. 
     Thus, when the flat pouch sheet is placed between the upper mold  30  and the lower mold  20 , the upper mold  30  may descend to the lower mold  20  (or the lower mold ascends to the upper mold) to press the pouch sheet between the upper mold  30  and the lower mold  20 . 
     After the pressing is performed, when the upper mold  30  and the lower mold  20  are separated from each other, the first seating part  1  and the second seating part  12  are formed on a portion of the pouch sheet, which is pressed by the flat portion  31 , and the sidewall  13  which connects the first seating part  11  to the second seating part  12  and forms a surface parallel to a side surface of the electrode assembly  1  when the electrode assembly  1  is mounted is formed is formed on a portion of the pouch sheet, which is pressed by the protrusion  32 . 
     Here, each of an edge portion of the upper mold  30  and an edge portion of the protrusion  32 , which are inserted into the first groove  21 , may be rounded at a predetermined curvature, and an edge portion of the lower mold  20 , in which the first groove  21  is formed, may be rounded at a predetermined curvature. This is done for preventing the pouch sheet from being damaged during the pressing when a pressure is concentrated into the edge portion. The curvature may also be determined according to the elongation rate of the metal layer of the pouch sheet. 
     Second Embodiment 
     The present invention provides a pouch capable of being manufactured using the apparatus for molding the pouch according to the first embodiment as a second embodiment. 
       FIG.  3    is a cross-sectional view illustrating a state in which an electrode assembly  1  is mounted in the pouch  10  manufactured using the apparatus for molding the pouch of FIG.  2 . Referring to the drawings, the pouch  10  provided in this embodiment comprises a first seating part  11  and a second seating part  12 , which are connected to each other. When the electrode assembly  1  is mounted, the first seating part  11  and the second seating part  12  are respectively folded to cover top and bottom surfaces of the electrode assembly  1  so as to be sealed in a state in which sealing portions  11   a  and  12   a  of the first seating part  11  and the second seating part  12  are in contact with each other. 
     Here, the first seating part  11  covers one of upper and lower portions of the electrode assembly  1 , and the second seating part  12  covers the other one of the upper and lower portions of the electrode assembly  1 . 
     Also, the first seating part  11  and the second seating part  12  are connected to each other through a sidewall  13  of which one side is connected to one side of the first seating part  11 , and the other side is connected to the second seating part  12 . 
     The sidewall  13  may be folded so as to be perpendicular to the first seating part  11  and the second seating part  12  and be formed in a flat planar shape on both inner and outer surfaces of the pouch  10 . 
     That is, in the structure according to the related art, a bent point C is formed at a point at which the first seating part  3  and the second seating part  4  are connected to each other to provide a portion that protruding outward from the pouch, and thus, the pouch is not flat. However, in the structure according to this specification, since the first seating part  11  and the second seating part  12  are bent at both ends of the sidewall  13 , respectively, the bent point C may be removed, and thus, all of inner and outer surfaces of the pouch  10  may have flat planar shapes. Thus, the pouch  10  according to this specification may have a cleaner appearance compared to the structure according to the related art. 
     For reference, the expression ‘perpendicular’ described in the present invention does not mean only an exact right angle, but mean a state that is approximately adjacent to the right angle when bending occurs between two components. 
     Referring to  FIG.  4   , when the pouch is molded by the apparatus for molding the pouch according to the present invention, a pouch capable of accommodating the accommodating the electrode having a significantly thicker thickness may be manufactured. Thus, as the thickness of the electrode assembly increases, the sidewall  13  may stands vertically with the first seating part  11  and the second seating part  12 . 
     Therefore, the pouch according to this specification has a significantly more vertical shape compared to that according to the related art. Therefore, since the word vertical is used to express this state, the word vertical in this specification should not be interpreted as meaning only a right angle of 90 degrees. 
     For example, when the sidewall is folded at the first seating part or the second seating part, even though each of the first seating part and the second seating part is bent at an angle of 80 degrees or 100 degrees according to the increasing thickness of the electrode assembly, this may be considered as the vertically folded category if it may be considered as the pouch according to this specification. 
     Also, in the present invention, it should be understood as the meaning that the sidewall has a shape as a ‘flat plane’ does not mean only a state of a completely flat surface having a curvature of 0 because a radius of curvature infinitely increases at all points, but rather than a point or a curved shape as a whole compared to the related art. 
     Also, since the pouch is manufactured by laminating a thin metal layer and a resin layer, the pouch may be easily deformed by external force. Thus, if the pouch is manufactured without being curved or bent as a whole, when the pouch has a partial wrinkled shape or a slightly bent portion, it also should be regarded as being within the category of the ‘flat plane’. 
     Furthermore, like the structure according to the related art, each of the first seating part  11  and the second seating part  12  is formed so that the sealing portion  11   a  and  12   a  extend from remaining sides except of a side connected to the sidewall  13 . When the electrode assembly  1  is mounted to be folded, the sealing portion  11   a  of the first seating part  11  and the sealing portion  12   a  of the second seating part  12  are bonded to be sealed in a state of being in contact with each other. 
     Here, each of the sealing portions  11   a  and  12   a  may have a sufficient length so that the sealing portions  11  and  12   a  adhere to each other by the length of the sidewall  13 . That is, when the first seating part  11  and the second seating part  12  are folded to be parallel to each other, the extending length of each of the sealing portion  11   a  of the first seating part and the sealing portion  12   a  of the second seating part, which respectively extend from the first seating part  11  and the second seating part  12 , is determined according to the length of the sidewall  13  so that the sealing portion  11   a  of the first seating part and the sealing portion  12   a  of the second seating part are sealed. 
     A stepped portion  14  having a concavely recessed shape may be formed in each of an edge at which the first seating part  11  and the sidewall  13  are connected to each other and an edge which the second seating part  12  and the sidewall  13  are connected to each other. When the stepped portion  14  is molded in the above-described molding apparatus, if the resin layer stacked on the metal layer is a thermosetting resin, when a point that is pressed by the protrusion  32  and the second groove  22  is curved, each of the first seating part  11  and the seating part  12  may be bent at a position except for the point to form the stepped portion  14 . As a result, if the resin layer of the pouch sheet has thermoplastic properties rather than thermosetting properties, the stepped portion  14  may not be formed. 
     In the pouch  10  having the above-described configuration as described above according to the present invention, the sidewall  13  connecting the first seating part  11  to the second seating part  12  may be formed to mount the electrode assembly  1  having a thicker thickness by adjusting the thickness of the sidewall  13 . 
     As illustrated in  FIG.  4   , which illustrates the state, in which the electrode assembly is mounted in the pouch according to the related art and the state, in which the electrode assembly having the thicker thickness is mounted in the pouch according to the present invention, in the pouch  2  according to the related art, the thickness of the mountable electrode assembly  1  is limited because the elongation of the metal layer is limited, but in the pouch  10  according to the present invention, the sidewall  13  has a flat surface that is not elongated between the upper mold  30  and the lower mold  20 , and thus, a length of the flat surface is adjusted to mount the electrode assembly having the thicker thickness. 
     Third Embodiment 
     The present invention provides a method for manufacturing a secondary battery comprising the pouch according to the second embodiment as a third embodiment. 
     A method for manufacturing a secondary battery according to this embodiment comprises a pouch molding step (S 10 ) of molding a pouch and a sealing step (S 20 ) of embedding an electrode assembly and an electrolyte in the molded pouch to seal a sealing portion of the pouch. 
     Here, the pouch molding step (S 10 ) comprises a step (S 11 ) of seating a pouch sheet on a lower mold  20  in which a first groove  21  recessed by a predetermined depth from a top surface thereof, and a second groove  22  is additionally recessed from a bottom surface of the first groove  21 , and a step (S 12 ) of pressing the pouch sheet to mold the pouch by using an upper mold  30  on which a flat portion  31  is formed on one surface thereof, which is inserted into the first groove  21 , and a protrusion  32  inserted into the second groove  22  protrudes from the flat portion  31 . Here, when the pouch sheet is pressed to be molded, a portion formed as a sidewall is molded so that each of both inner and outer surfaces has a flat planar shape. 
     Also, the pouch molding step (S 10 ) comprises a step (S 13 ) of folding the molded pouch. In this step, the pouch sheet is folded so that a first seating part  11  and a second seating part  12 , which face each other, and a sidewall  13  connecting the first seating part  11  to the second seating part  12  are formed. 
     Here, in the step (S 13 ) of folding the molded pouch sheet, the pouch sheet is folded so that the sidewall  13  is perpendicular to each of the first seating part  11  and the second seating part  12 . 
     When the electrode assembly  1  and the electrolyte are embedded in the pouch manufactured as described above, heat and a pressure are applied to sealing portions of the pouch to perform the sealing step (S 20 ). 
     While the embodiments of the present invention have been described with reference to the specific embodiments, it will be apparent to those skilled in the art that various changes and modifications may be made without departing from the spirit and scope of the invention as defined in the following claims. 
     DESCRIPTION OF THE SYMBOLS 
       1 : Electrode assembly 
       10 : Pouch 
       11 : First seating part 
       12 : Second seating part 
       20 : Lower mold 
       21 : First groove 
       22 : Second groove 
       30 : Upper mold 
       31 : Flat portion 
       32 : Protrusion