Patent Publication Number: US-2023145850-A1

Title: Sheet Cutting and Fusion Apparatus

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present application is a national phase entry under 35 U.S.C. § 371 of International Application No. PCT/KR2022/001577 filed on Jan. 28, 2022, and now published as International Publication No. WO 2022/169220, which claims priority from Korean Patent Application No. 10-2021-0016767 filed on Feb. 5, 2021, all of which are hereby incorporated herein by reference in their entireties. 
    
    
     FIELD 
     The present invention relates to a sheet cutting and fusion apparatus. More particularly, the present invention relates to a sheet cutting and fusion apparatus including a structure in which steps are formed at an upper cutter and a lower cutter such that two or more sheets can be simultaneously cut and fused. 
     BACKGROUND 
     A lithium secondary battery may be manufactured using a method of receiving an electrode assembly, configured to have a structure in which a positive electrode, a sheet, and a negative electrode are sequentially stacked, in a battery case and hermetically sealing the battery case. 
     A sheet cutting and fusion apparatus according to the present invention is applicable to any sheet as long as the sheet is thin, as in a separator used in a battery, and is configured such that a part of one sheet and a part of another sheet can be melted and coupled to each other. When a sheet described throughout the specification is applied to a battery, the sheet refers to a separator that is generally used. 
     The electrode assembly includes a single-cell configured to have a structure in which a first electrode and a sheet are stacked, a mono-cell configured to have a structure in which a first electrode, a sheet, and a second electrode are stacked, or a bi-cell configured to have a structure in which a first electrode, a sheet, a second electrode, a sheet, and a third electrode are stacked. In addition, a sheet may be further added to an outer surface of the first electrode or the second electrode of the mono-cell, or a sheet may be further added to an outer surface of the first electrode or the third electrode of the bi-cell. 
     Each of the electrodes constituting the electrode assembly is manufactured by applying an electrode mixture to one surface or opposite surfaces of a thin current collector made of copper, aluminum, or nickel, drying and pressing the same, and cutting the same into a unit electrode. 
     The unit electrode thus manufactured is stacked and laminated in the state in which a sheet is interposed between a positive electrode and a negative electrode, whereby a unit cell is manufactured. 
     In the mono-cell, the sheet is interposed between the first electrode and the second electrode, and another sheet is located at the surface opposite the surface of the first electrode or the second electrode that faces the sheets. 
     In order to manufacture a unit cell configured such that two electrodes and two sheets are stacked or a unit cell configured such that two electrodes and two or three sheets are stacked, as described above, the first sheet having the first electrode disposed thereon and the second sheet having the second electrode disposed thereon are disposed and laminated such that the first electrode and the second electrode overlap each other, and then the first sheet and the second sheet are cut. 
     The first sheet and the second sheet are moved to a subsequent step of the process in the state in which the first sheet and the second sheet are cut. When the first sheet and the second sheet are folded or deviate from the original positions thereof, the electrodes may be exposed, which may cause serious problems related to safety, such as short circuit in a battery cell and outbreak of fire during use of the battery cell. 
     In connection therewith,  FIG.  1    is a schematic view of a conventional sheet cutting apparatus,  FIG.  2    is a sectional view showing a sequence of sheet cutting performed by the conventional sheet cutting apparatus, and  FIG.  3    is a schematic view showing the construction of an upper cutter and a lower cutter when the conventional sheet cutting apparatus is applied to two sheets. 
     Referring to  FIGS.  1  to  3   , a first electrode  10  is disposed on an upper sheet, which is one of two sheets  30  that overlap each other, and a second electrode  20  is disposed on a lower sheet. 
     An upper cutter  40  and a lower cutter  50  configured to cut the sheets are disposed at the uppermost surface and the lowermost surface of the sheets  30 , respectively. 
     The upper cutter  40  includes a first cutting surface  43 , which is a surface configured to cut the sheets  30  while overlapping the lower cutter  50  a lower surface  44  configured to face the sheets  30  in parallel thereto, and an inclined portion  45 , which is a surface inclined relative to the sheets. The lower cutter  50  includes a second cutting surface  53 , which is a surface configured to cut the sheets  30  while overlapping the upper cutter  40 , and an upper surface  54  configured to face the sheets  30  in parallel thereto. 
     The upper cutter  40  is configured such that the lower surface  44  and the first cutting surface  43  perpendicularly join each other, and the lower cutter  50  is configured such that the upper surface  54  and the second cutting surface  53  perpendicularly join each other. When the first cutting surface  43  and the second cutting surface  53  intersect each other, therefore, the sheets  30  are cut. 
     In the case in which the sheet cutting apparatus shown in  FIGS.  1  to  3    is used, therefore, the sheets may be cut; however, the sheets may be transferred to a subsequent process in the state in which surplus portions of the sheets extending farther than outer peripheries of the electrodes are not fixed. At this time, the surplus portions of the sheets may be folded, or the sheets may be separated from each other. 
     In connection therewith, Patent Document 1 discloses a pair of blades configured to be rotated in opposite directions in order to cut a separator (a sheet) on which electrodes are sequentially disposed spaced apart from each other. In Patent Document 1, the blades are configured to cut two sheets in order to manufacture a mono-cell or a bi-cell including two sheets; however, the blades exhibit only a function of cutting the sheets. 
     Patent Document 2 discloses a separator (sheet) cutting apparatus including a cutter member configured to cut a sheet and a heat transfer unit having a heating member configured to heat the cutter member, wherein the sheet is heated to a melting temperature thereof or higher in order to cut the sheet. 
     In Patent Document 2, the sheet is melted in order to achieve an effect in that a reinforcement portion having a smooth surface is formed on a cut section of the sheet when the melted sheet is hardened, and only cutting of a single sheet is disclosed. Consequently, technology for preventing two or more sheets from being folded during a transfer process is not disclosed. 
     Patent Document 3 discloses a slitter configured to cut a separator (sheet), wherein first slitting knives and second slitting knives configured to cut the sheet each include a heating portion in order to shrink a cut section of the sheet. 
     In Patent Document 3, the heating portion is provided to shrink the cut section of the sheet; however, the first slitting knives and the second slitting knives are used in a slitting process. That is, Patent Document 3 does not disclose technology for preventing dislocation of two or more stacked sheets. 
     Therefore, there is a need for technology capable of preventing exposure of an electrode stacked on a sheet due to folding of the sheet or change in position of the sheet when the sheet is moved to a subsequent electrode manufacturing process in the state in which the sheet is cut while not changing the electrode manufacturing process. 
     PRIOR ART DOCUMENTS 
     
         
         Korean Registered Patent Publication No. 2169008 (2020 Oct. 16) (“Patent Document 1”) 
         Korean Registered Patent Publication No. 2003471 (2019 Jul. 18) (“Patent Document 2”) 
         Korean Registered Patent Publication No. 1608634 (2016 Mar. 29) (“Patent Document 3”) 
       
    
     SUMMARY OF THE DISCLOSURE 
     The present invention has been made in view of the above problems, and it is an object of the present invention to provide a sheet cutting and fusion apparatus including a structure in which steps are formed at an upper cutter and a lower cutter such that two or more sheets can be simultaneously cut and fused. 
     It is another object of the present invention to provide a sheet cutting and fusion apparatus capable of simultaneously cutting and fusing sheets of a unit cell such that the state in which the sheets are stably fixed is maintained when the sheets are transferred to a subsequent process in the state in which the sheets are cut without increasing the number of electrode manufacturing steps. 
     A sheet cutting and fusion apparatus according to the present invention is applicable to any sheet as long as the sheet is thin, as in a separator used in a battery, and is configured such that a part of one sheet and a part of another sheet can be melted and coupled to each other. 
     In order to accomplish the above objects, the present invention provides a sheet cutting and fusion apparatus including an upper cutter disposed at the uppermost surface of at least two sheets that overlap each other; and a lower cutter disposed at the lowermost surface of the sheets, wherein the upper cutter includes a first cutting surface configured to come into contact with the lower cutter without any step when the upper cutter is moved vertically; a first fusion portion constituted by a surface parallel to the first cutting surface in the state in which a first step is formed so as to extend from the first cutting surface; a lower surface configured to face the sheets; and a first connection portion constituted by a curved corner that connects the lower surface and the first fusion portion to each other, and 
     the lower cutter includes a second cutting surface configured to come into contact with the upper cutter without any step when the lower cutter is moved vertically; a second fusion portion constituted by a surface parallel to the second cutting surface in the state in which a second step is formed so as to extend from the second cutting surface; an upper surface configured to face the sheets; and a second connection portion constituted by a curved corner that connects the upper surface and the second fusion portion to each other. 
     Each of the upper cutter and the lower cutter may include a structure capable of being heated. 
     The upper cutter and/or the lower cutter may be moved such that the first cutting surface and the second cutting surface come into contact with each other without any step, and the sheets may be cut due to compression, shearing force, or melting by intersection between the first cutting surface and the second cutting surface. 
     Alternatively, the upper cutter and/or the lower cutter may be moved such that the first cutting surface and the second cutting surface overlap each other, and the sheets may be cut due to compression, shearing force, or melting by the first fusion portion and the second fusion portion. 
     Alternatively, the upper cutter and/or the lower cutter may be moved such that the first cutting surface and the second cutting surface overlap each other, and the sheets may be cut due to compression, shearing force, or melting by the first step and the second step. 
     When the sheets are disposed at any one of between the first cutting surface and the second cutting surface, between the first fusion portion and the second fusion portion, and between the first step and the second step, the sheets may be fused. 
     The first cutting surface, the first fusion portion, the second cutting surface, and the second fusion portion may have the same temperature, and the temperature thereof may be lower than the temperature of the first step and the second step. 
     The upper cutter may be disposed at the uppermost surface of the sheets, the lower cutter may be disposed at the lowermost surface of the sheets, and the lower surface of the upper cutter and the upper surface of the lower cutter may be disposed parallel to the sheets. 
     Alternatively, the upper cutter may be disposed at the uppermost surface of the sheets, the lower cutter may be disposed at the lowermost surface of the sheets, and the lower surface of the upper cutter and the upper surface of the lower cutter may be disposed inclined relative to the sheets. 
     The sheets may include a first sheet and a second sheet stacked in the state in which electrodes are interposed therebetween, the stacked electrodes and other stacked electrodes may be disposed spaced apart from each other by a predetermined distance, and the predetermined distance may be greater than the sum of the length from the first connection portion to the first cutting surface and the length from the second connection portion to the second cutting surface. 
     The height of each of the first step and the second step may be equal to or less than the thickness of at least two sheets that overlap each other. 
     In addition, the present invention provides a unit cell manufactured by cutting sheets using the sheet cutting and fusion apparatus, wherein the unit cell is a mono-cell configured such that a sheet, a first electrode, a sheet, a second electrode are stacked or a bi-cell configured such that a first electrode, a sheet, a second electrode, a sheet, and a first electrode are stacked, and sheets of one-direction outer peripheries of each of the mono-cell and the bi-cell parallel to each other are thermally fused. 
     In addition, the present invention may provide various combinations of the above solving means. 
     As is apparent from the above description, a sheet cutting and fusion apparatus according to the present invention is capable of cutting at least two sheets that overlap each other and fusing outer peripheries of the sheets, whereby it is possible to prevent the sheets from being folded or crumpled during a transfer process. 
     In addition, the structure of each of an upper cutter and a lower cutter configured to cut the sheets may be changed in order to simultaneously cut and fuse the sheets, whereby it is possible to simultaneously cut and fuse the sheets through a signal process. 
     Consequently, a separate apparatus or space for sheet fusion is not required. 
     In addition, when stepped surfaces of the upper cutter and the lower cutter abut each other, the sheets may be melted and cut. In this case, necessity for managing parallelism tolerance of the upper cutter and the lower cutter may be lowered, and the replacement cycle of the upper cutter and the lower cutter due to wear thereof may be lengthened, whereby management of a manufacturing process is easy. 
     In addition, since the number of stops of the manufacturing process may be reduced, whereby yield may be improved. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    is a schematic perspective view of a conventional sheet cutting apparatus. 
         FIG.  2    is a cross-sectional view showing a sequence of sheet cutting performed by the conventional sheet cutting apparatus. 
         FIG.  3    is a schematic elevation view showing the construction of an upper cutter and a lower cutter when the conventional sheet cutting apparatus is applied to two sheets. 
         FIG.  4    is an elevation view showing a sheet cutting and fusion apparatus according to a first embodiment. 
         FIG.  5    is an elevation view showing a sheet cutting and fusion apparatus according to a second embodiment. 
         FIG.  6    is a set of elevation views showing a process of cutting and fusing sheets using the sheet cutting and fusion apparatus according to the second embodiment. 
         FIG.  7    is a set of elevation views showing a process of cutting and fusing sheets using a sheet cutting and fusion apparatus according to a third embodiment. 
         FIG.  8    is a view showing a unit cell manufactured using the sheet cutting and fusion apparatus according to a further embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     Now, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings such that the preferred embodiments of the present invention can be easily implemented by a person having ordinary skill in the art to which the present invention pertains. In describing the principle of operation of the preferred embodiments of the present invention in detail, however, a detailed description of known functions and configurations incorporated herein will be omitted when the same may obscure the subject matter of the present invention. 
     In addition, the same reference numbers will be used throughout the drawings to refer to parts that perform similar functions or operations. In the case in which one part is said to be connected to another part throughout the specification, not only may the one part be directly connected to the other part, but also, the one part may be indirectly connected to the other part via a further part. In addition, that a certain element is included does not mean that other elements are excluded, but rather means that such elements may be further included unless mentioned otherwise. 
     In addition, a description to embody elements through limitation or addition may be applied to all inventions, unless particularly restricted, and does not limit a specific invention. 
     Also, in the description of the invention and the claims of the present application, singular forms are intended to include plural forms unless mentioned otherwise. 
     Also, in the description of the invention and the claims of the present application, “or” includes “and” unless mentioned otherwise. Therefore, “including A or B” means three cases, namely, the case including A, the case including B, and the case including A and B. 
     Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. 
       FIGS.  4  to  8    illustrate embodiments of a sheet cutting and fusion apparatus according to the present invention. In  FIGS.  4  to  8   , a sheet used for a battery, i.e. a separator, is described by way of example. However, the sheet cutting and fusion apparatus according to the present invention is applicable to any sheet as long as the sheet is thin and is configured such that a part of one sheet and a part of another sheet can be melted and coupled to each other. 
     Referring to  FIG.  4   , first electrodes  10  are disposed spaced apart from each other by a predetermined distance W on an upper surface of an upper sheet  30 , which is one of sheets that overlap each other, and second electrodes  20  are disposed spaced apart from each other by the predetermined distance W on an upper surface of a lower sheet  30 , which is the other of the sheets that overlap each other. 
     The first electrodes  10  and the second electrodes  20  pass through the sheet cutting and fusion apparatus, which is constituted by an upper cutter  100  and a lower cutter  200 , in a state of being disposed so as to completely overlap each other in a y-axis direction, which is a stacking direction, whereby the two sheets  30  that overlap each other may be cut while outer peripheries of the sheets  30  are adhered to each other by thermal fusion. 
     Specifically, a sheet cutting and fusion apparatus according to a first embodiment includes an upper cutter  100  disposed at the uppermost surface of at least two sheets  30  that overlap each other and a lower cutter  200  disposed at the lowermost surface of the sheets  30 , wherein the upper cutter  100  includes a first cutting surface  130  configured to come into contact with the lower cutter  200  without any step when the upper cutter is moved vertically, a first fusion portion  120  constituted by a surface parallel to the first cutting surface  130  in the state in which a first step  110  is formed so as to extend from the first cutting surface  130 , a lower surface  140  configured to face the sheets  30 , and a first connection portion  150 , which is a curved corner that connects the lower surface  140  and the first fusion portion  120  to each other. 
     The lower cutter  200  includes a second cutting surface  230  configured to come into contact with the upper cutter  100  without any step when the lower cutter is moved vertically, a second fusion portion  220  constituted by a surface parallel to the second cutting surface  230  in the state in which a second step  210  is formed so as to extend from the second cutting surface  230 , an upper surface  240  configured to face the sheets  30 , and a second connection portion  250 , which is a curved corner that connects the upper surface  240  and the second fusion portion  220  to each other. 
     The sheet cutting and fusion apparatus according to the present invention simultaneously performs a process of cutting the sheets and a process of thermally fusing the outer peripheries of the sheets. Specifically, each of the first connection portion  150 , which connects the first fusion portion  120  of the first cutting surface  130  and the lower surface  140  to each other, and the second connection portion  250 , which connects the second fusion portion  220  of the second cutting surface  230  and the upper surface  240  to each other, is formed in a curved shape. 
     In addition, the step is formed between the first cutting surface  130  and the first fusion portion  120 , the step is formed between the second cutting surface  230  and the second fusion portion  220 , and the first cutting surface  130  and the second cutting surface  230  are moved so as not to overlap each other. 
     Even though the lowermost end of the upper cutter and the uppermost end of the lower cutter intersect so as to be adjacent to each other, therefore, the sheets are not cut, since an empty space is formed therebetween. 
     In addition, each of the upper cutter and the lower cutter includes a structure capable of being heated. 
     That is, each of the upper cutter and the lower cutter may be configured such that the temperature thereof can be increased to a temperature at which the sheets are melted. 
     When the sheets are cut using the upper cutter and the lower cutter, the temperature of each of which has been increased to the sheet melting temperature, sheet adhesion portions at which the melted sheets are attached to each other are formed at opposite sides of a cutting line. 
     The upper cutter  100  and/or the lower cutter  200  may be moved such that the first cutting surface  130  and the second cutting surface  230  come into contact with each other without any step, and the sheets  30  may be cut due to compression, shearing force, or melting by intersection between the first cutting surface  130  and the second cutting surface  230 . 
     The sheet cutting and fusion apparatus shown in  FIG.  4    is configured such that, in the state in which the upper cutter  100  is disposed at the upper surface of one of the sheets  30  and the lower cutter  200  is disposed at the lower surface of the other of the sheets  30 , the lower surface  140  of the upper cutter  100  and the upper surface  240  of the lower cutter  200  are disposed parallel to the sheets  30 . 
     Consequently, the electrodes and the sheets  30  moving between the upper cutter  100  and the lower cutter  200  may be supported thereunder. 
       FIG.  5    is a view showing a sheet cutting and fusion apparatus according to a second embodiment of the present invention. 
     Referring to  FIG.  5   , first electrodes  10  are disposed spaced apart from each other by a predetermined distance W on an upper surface of an upper sheet  30 , which is one of sheets that overlap each other, and second electrodes  20  are disposed spaced apart from each other by the predetermined distance W on an upper surface of a lower sheet  30 , which is the other of the sheets that overlap each other. 
     The first electrodes  10  and the second electrodes  20  pass through the sheet cutting and fusion apparatus, which is constituted by an upper cutter  300  and a lower cutter  400 , in a state of being disposed so as to completely overlap each other in a y-axis direction, which is a stacking direction, whereby the two sheets  30  that overlap each other may be cut while outer peripheries of the sheets  30  are adhered to each other by thermal fusion. 
     Specifically, the sheet cutting and fusion apparatus according to the second embodiment includes an upper cutter  300  disposed at the uppermost surface of at least two sheets  30  that overlap each other and a lower cutter  400  disposed at the lowermost surface of the sheets  30 , wherein the upper cutter  300  includes a first cutting surface  330  configured to come into contact with the lower cutter  400  without any step when the upper cutter is moved vertically, a first fusion portion  320  constituted by a surface parallel to the first cutting surface  330  in the state in which a first step  310  is formed so as to extend from the first cutting surface  330 , a lower surface  340  configured to face the sheets  30 , and a first connection portion  350 , which is a curved corner that connects the lower surface  340  and the first fusion portion  320  to each other. 
     The lower cutter  400  includes a second cutting surface  430  configured to come into contact with the upper cutter  300  without any step when the lower cutter is moved vertically, a second fusion portion  420  constituted by a surface parallel to the second cutting surface  430  in the state in which a second step  410  is formed so as to extend from the second cutting surface  430 , an upper surface  440  configured to face the sheets  30 , and a second connection portion  450 , which is a curved corner that connects the upper surface  440  and the second fusion portion  420  to each other. 
     The sheet cutting and fusion apparatus according to the present invention simultaneously performs a process of cutting the sheets and a process of thermally fusing the outer peripheries of the sheets. Specifically, each of the first connection portion  350 , which connects the first fusion portion  320  of the first cutting surface  330  and the lower surface  340  to each other, and the second connection portion  450 , which connects the second fusion portion  420  of the second cutting surface  430  and the upper surface  440  to each other, is formed in a curved shape. 
     In addition, the step is formed between the first cutting surface  330  and the first fusion portion  320 , the step is formed between the second cutting surface  430  and the second fusion portion  420 , and the first cutting surface  330  and the second cutting surface  430  are moved so as not to overlap each other. 
     Even though the lowermost end of the upper cutter and the uppermost end of the lower cutter intersect so as to be adjacent to each other, therefore, the sheets are not cut, since an empty space is formed therebetween. 
     In addition, each of the upper cutter and the lower cutter includes a structure capable of being heated. 
     That is, each of the upper cutter and the lower cutter may be configured such that the temperature thereof can be increased to a temperature at which the sheets are melted. 
     When the sheets are cut using the upper cutter and the lower cutter, the temperature of each of which has been increased to the sheet melting temperature, sheet adhesion portions at which the melted sheets are attached to each other are formed at opposite sides of a cutting line. 
     The sheet cutting and fusion apparatus shown in  FIG.  5    is configured such that, in the state in which the upper cutter  300  is disposed at the upper surface of one of the sheets  30  and the lower cutter  400  is disposed at the lower surface of the other of the sheets  30 , the lower surface  340  of the upper cutter  300  and the upper surface  440  of the lower cutter  400  are disposed inclined relative to the sheets  30 . 
       FIG.  6    is a view showing a process of cutting and fusing sheets using the sheet cutting and fusion apparatus according to the second embodiment of the present invention. 
     Referring to  FIG.  6   , when sheets  30  are interposed between the first cutting surface  330  and the second fusion portion  420  and between the second cutting surface  430  and the first fusion portion  320  in an overlapping state, the sheets are melted by the upper cutter  300  and the lower cutter  400 , which are heated, whereby a thermally fused portion  370  is formed. 
     The upper cutter  300  is moved downwards such that the first cutting surface  330  and the second cutting surface  430  face each other in tight contact with each other, and the sheets are melted and adhered to each other before intersection between the first cutting surface  330  and the second cutting surface  430 . When the first cutting surface  330  and the second cutting surface  430  intersect each other, particularly when the first corner  360  and the second corner  460  abut each other, the sheets  30  are cut. 
     Consequently, the two sheets are cut in the state in which the outer peripheries of the sheets are coupled to each other by thermal fusion while the sheets overlap each other. 
     In consideration of the fact that the two sheets are attached to each other in a state of being in tight contact with each other between the first cutting surface of the upper cutter and the second fusion portion of the lower cutter and between the first fusion portion of the upper cutter and the second cutting surface of the lower cutter, the height H of each of the first step  310  and the second step  410  may be equal to or less than the thickness of at least two sheets that overlap each other. 
     Referring to  FIGS.  5  and  6    together, the sheets include a first sheet and a second sheet stacked in the state in which electrodes are interposed therebetween, the electrodes are disposed spaced apart from each other by a predetermined distance W, and the distance W is greater than the sum of the length from the first connection portion  350  to the first cutting surface  330  and the length from the second connection portion  450  to the second cutting surface  430 . In the case in which the distance W between the electrodes is set, as described above, the electrodes are not pressed when the upper cutter and the lower cutter intersect each other, whereby it is possible to prevent damage to the electrodes. In addition, the electrodes may not be disposed at the first connection portion and the second connection portion, whereby it is possible to prevent the electrodes from being separated from the sheets. 
       FIG.  7    is a view showing a process of cutting and fusing sheets using a sheet cutting and fusion apparatus according to a third embodiment of the present invention. 
     Referring to  FIG.  7   , an upper cutter  500  is moved downwards such that a first cutting surface  530  of the upper cutter  500  and a second cutting surface  630  of a lower cutter  600  overlap each other, the first cutting surface  530  of the upper cutter  500  and the second cutting surface  630  of the lower cutter  600  do not intersect each other, and the upper cutter is moved downwards until a first step  510  comes into tight contact with a second step  610  in the state in which sheets are located therebetween. 
     The two sheets  30  are attached to each other in tight contact with each other between the first cutting surface  530  of the upper cutter and a second fusion portion  620  of the lower cutter and between a first fusion portion  520  of the upper cutter and the second cutting surface  630  of the lower cutter, whereby a thermally fused portion  370  is formed. 
     When the upper cutter  500  is further moved downwards and thus at least a part of the first step  510  and at least a part of the second step  610  face each other in tight contact with each other, the sheets  30  are cut. 
     In the sheet cutting and fusion apparatus having the structure as shown in  FIG.  7   , the sheets  30  may be cut due to compression, shearing force, or melting by the first step  510  and the second step  610 . Even though a sharp structure, such as a cutter, is not provided at each of the first step  510  and the second step  610 , therefore, a smooth cut section may be formed after the sections of the cut sheets are cooled. 
     The first cutting surface  530 , the first fusion portion  520 , the second cutting surface  630 , and the second fusion portion  620  may have the same temperature, and the temperature of the first cutting surface  530 , the first fusion portion  520 , the second cutting surface  630 , and the second fusion portion  620  may be lower than the temperature of the first step  510  and the second step  610 , such that the sheets are melted and separated from each other at the first step  510  and the second step  610  and such that the sheets, brought into tight contact with each other between the first cutting surface  530  and the second fusion portion  620  and between the second cutting surface  630  and the first fusion portion  520 , are melted and adhered to each other, as described above. 
     For example, a sheet according to the present invention may be a sheet including a polyolefin-based material. As another example, the sheet may include a substrate made of a polyolefin-based material, including polyethylene and polypropylene, and an inorganic coating layer formed on one surface or opposite surfaces of the substrate. The inorganic coating layer may be constituted by a mixture of an inorganic material capable of improving heat resistance and a binder configured to bind particles of the inorganic material. 
     For example, the temperature of the first cutting surface  530 , the first fusion portion  520 , the second cutting surface  630 , and the second fusion portion  620  may be set to a range of 80° C. to 150° C., and the temperature of the first step  510  and the second step  610  may be set to a range of 160° C. to 200° C. 
     The upper cutter  500  and/or the lower cutter  600  may be moved such that the first cutting surface  530  and the second cutting surface  630  overlap each other, and the sheets may be fused or cut due to compression, shearing force, or melting by the first fusion portion  520  and the second fusion portion  620 . 
     In the case in which any one of the sheet cutting and fusion apparatuses shown in  FIGS.  4  to  7    is used, the sheets may be fused when the sheets are disposed at any one of between the first cutting surface and the second cutting surface, between the first fusion portion and the second fusion portion, and between the first step and the second step. 
     When the upper cutter  100 ,  300 , or  500  and the lower cutter,  200 ,  400 , or  600  of the sheet cutting and fusion apparatus according to the present invention are continuously used, edges of the first step  110 ,  310 , or  510 , the first cutting surface  130 ,  330 , or  530 , the second step  210 ,  410 , or  610 , and the second cutting surface  230 ,  430 , or  630  may become dull. In the case in which the edges are slightly worn, only the first step  110 ,  310 , or  510 , the first cutting surface  130 ,  330 , or  530 , the second step  210 ,  410 , or  610 , and the second cutting surface  230 ,  430 , or  630  may be newly machined. In the case in which the sizes of the first step  110 ,  310 , or  510  and the second step  210 ,  410 , or  610  are reduced, whereby cutting and fusion according to the present invention are not simultaneously performed, the lower surface  140  or  340 , the first connection portion  150 ,  350 , or  550 , the upper surface  240  or  440 , and the second connection portion  250 ,  450 , or  650  are also machined. 
       FIG.  8    is a view showing a unit cell manufactured using the sheet cutting and fusion apparatus according to the present invention. 
     Referring to  FIG.  8   , the unit cell is a bi-cell configured such that a first electrode  10 , a sheet  30 , a second electrode  20 , a sheet  30 , and a first electrode  10  are stacked. Sheets of one-direction outer peripheries of the bi-cell parallel to each other are thermally fused, whereby thermally fused portions  370  are formed. 
     When the bi-cell is transferred to a subsequent electrode manufacturing process, therefore, the state in which the sheets are stably attached to each other may be maintained, whereby it is possible to prevent short circuit or outbreak of fire due to exposure of the electrodes. 
     Those skilled in the art to which the present invention pertains will appreciate that various applications and modifications are possible within the category of the present invention based on the above description. 
     DESCRIPTION OF REFERENCE SYMBOLS 
     
         
         
           
               10 : First electrode 
               20 : Second electrode 
               30 : Sheet 
               40 ,  100 ,  300 ,  500 : Upper cutters 
               110 ,  310 ,  510 : First steps 
               120 ,  320 ,  520 : First fusion portions 
               43 ,  130 ,  330 ,  530 : First cutting surfaces 
               44 ,  140 ,  340 : Lower surfaces 
               150 ,  350 ,  550 : First connection portions 
               360 : First corner 
               45 : Inclined portion 
               50 ,  200 ,  400 ,  600 : Lower cutters 
               210 ,  410 ,  610 : Second steps 
               220 ,  420 ,  620 : Second fusion portions 
               53 ,  230 ,  430 ,  630 : Second cutting surfaces 
               54 ,  240 ,  440 : Upper surfaces 
               250 ,  450 ,  650 : Second connection portions 
               460 : Second corner 
               370 : Thermally fused portion 
             W: Distance