Patent Publication Number: US-2023142103-A1

Title: Method of Manufacturing Electrode Including Folding Portion and Electrode Sheet Including Folding Portion

Description:
TECHNICAL FIELD 
     This application claims the benefit of priority to Korean Patent Application No. 2020-0070046 filed on Jun. 10, 2020, the disclosure of which is incorporated herein by reference in its entirety. 
     The present invention relates to a method of manufacturing an electrode including a folding portion and an electrode sheet including the folding portion, and more particularly to a method of manufacturing an electrode including a folding portion usable to manufacture a foldable battery cell and an electrode sheet including the folding portion. 
     BACKGROUND ART 
     A lithium secondary battery, which is capable of being charged and discharged, has been widely used as an energy source for wireless mobile devices or wearable devices, and has also been used as an energy source for electric vehicles and hybrid electric vehicles presented as alternatives to existing gasoline and diesel vehicles, which cause air pollution. 
     In addition, with an increase in kinds of miniaturized multifunctional products and a trend of emphasizing design in electronic devices, the number of products based on new shapes, such as a shape including a curve or a geometrical shape, other than conventional simple structures, such as a planar structure and a prismatic structure, has increased. 
     Lithium secondary batteries having various shapes, such as a stepped shape and a polygonal shape, other than a rectangular shape, have been developed in order to apply the lithium secondary batteries to such products having various shapes. 
     For example, for a smartphone, the side thereof is curved in order to improve sensation of grip, and flexible display products capable of being bent or folded have come on the stage. 
     In the case in which a rectangular battery cell is used in a bendable or foldable device, there is a problem in that dead space is formed in large numbers. Therefore, it is necessary to develop a battery cell capable of securing capacity while reducing dead space even though the battery cell is mounted in a device having an atypical shape. 
     In connection therewith, Patent Document 1 discloses a secondary battery configured such that a positive electrode active material layer and a negative electrode active material layer are formed by coating so as to be spaced apart from each other by a predetermined distance and including a bending region configured to be bent at an uncoated portion, which is not coated with the positive electrode active material layer and the negative electrode active material layer. 
     The secondary battery disclosed in Patent Document 1 is suitably applied to a long device but has a problem in that a plurality of bending regions is formed, whereby the uncoated portion is widened, and therefore energy density is lowered. 
     Patent Document 2 relates to a battery cell including a current collector having at least one uncoated portion that partitions an electrode mixture, wherein the portion of a battery case at which the uncoated portion is located is bent, whereby the shape of the battery cell is changed. 
     In Patent Document 2, an electrode assembly is separated from the battery case, whereby there is a problem in that a bent portion of the battery case and a bent portion of the electrode assembly may be misaligned with each other when the battery cell is bent. 
     Patent Document 3 discloses an electrode configured to have a structure in which an electrode active material is printed on a band type electrode current collector so as to have a pattern repeated at regular intervals. 
     However, the invention disclosed in Patent Document 3 relates to an electrode cut so as to have a predetermined length and width, wherein the electrode is received in a sheathing member in a state of being bent. 
     As can be seen from the above description, each of the above patent documents discloses only an electrode including an uncoated portion that is coated with no electrode mixture. Therefore, a method of manufacturing an electrode having the above structure or research on the shape of an electrode sheet is needed. 
     PRIOR ART DOCUMENTS 
     
         
         (Patent Document 1) Korean Patent Application Publication No. 2012-0022385 (2012.03.12) 
         (Patent Document 2) Korean Patent Application Publication No. 2017-0033513 (2017.03.27) 
         (Patent Document 3) Japanese Patent Application Publication No. 1995-153438 (1995.06.16) 
       
    
     DISCLOSURE 
     Technical Problem 
     The present invention has been made in view of the above problems, and it is an object of the present invention to provide a method of manufacturing an electrode including a folding portion constituted by an uncoated portion having no electrode mixture formed thereon by coating in order to manufacture an electrode for foldable battery cells and an electrode sheet including the folding portion. 
     Technical Solution 
     An electrode manufacturing method according to the present invention to accomplish the above object includes a coating step of forming an electrode mixture coated portion on an electrode sheet so as to include an uncoated portion having no electrode mixture formed thereon by coating; a step of slitting the electrode sheet into a plurality of unit electrode sheets; and a step of notching the slit electrode sheet, wherein the uncoated portion includes an electrode tab formation portion and a folding portion formed so as to be parallel to a direction in which the electrode sheet is taken out. 
     In the electrode manufacturing method according to the present invention, the coated portion may be continuously formed so as to be parallel to the direction in which the electrode sheet is taken out. 
     In the electrode manufacturing method according to the present invention, the slitting step may be a step of slitting a coated portion located between the folding portion and another folding portion adjacent to the folding portion. 
     The electrode manufacturing method according to the present invention may include a step of forming the uncoated portion such that the width of the electrode tab formation portion and the width of the folding portion are different from each other. 
     In the electrode manufacturing method according to the present invention, the notching step may include a notching process for forming an electrode tab at the electrode tab formation portion and a process of notching the electrode sheet along a notching line in order to divide the electrode sheet into unit electrode sheets. 
     In addition, the notching process for forming the electrode tab and the process of notching the electrode sheet along the notching line may be simultaneously performed. 
     In the electrode manufacturing method according to the present invention, the electrode tab formation portion may be formed at each of opposite side ends and a middle portion of the electrode sheet that is taken out. 
     The electrode sheet may be slit into unit electrode sheets having two kinds of widths. 
     An electrode sheet according to the present invention includes a coated portion having an electrode mixture formed thereon by coating and an uncoated portion having no electrode mixture formed thereon by coating, wherein the uncoated portion includes an electrode tab formation portion and a folding portion formed so as to be parallel to a direction in which the electrode sheet is taken out. 
     In the electrode sheet according to the present invention, the coated portion, the electrode tab formation portion, and the folding portion may be formed so as to be symmetrical with respect to a slitting line. 
     In the electrode sheet according to the present invention, the folding portion may be an uncoated portion formed between the slitting line and the electrode tab formation portion. 
     In the electrode sheet according to the present invention, a first coated portion and a second coated portion may be formed on opposite sides of the folding portion, and the first coated portion and the second coated portion may be formed so as to have the same size. 
     In the electrode sheet according to the present invention, the width of the folding portion may be greater than the thickness of the coated portion x Π. 
     In addition, the present invention provides a battery cell including an electrode manufactured using the electrode manufacturing method, wherein the battery cell is configured to be bendable at the folding portion of the electrode. 
     Advantageous Effects 
     As is apparent from the above description, in an electrode manufacturing method according to the present invention, in order to form not only an uncoated portion, which is an electrode tab formation portion, but also an uncoated portion, which is configured to manufacture a folded electrode, on an electrode sheet, a method of coating a portion of the electrode sheet with an electrode mixture is used, whereby it is possible to reduce the number of manufacturing steps as compared to a method of coating the entirety of the electrode sheet with the electrode mixture and then removing the coating and to reduce defects that may occur during a coating removal process. 
     Also, in a notching process for manufacturing a unit electrode, notching is performed such that a folding portion is included in the unit electrode, whereby it is possible to obtain a unit electrode having a coated portion and an uncoated portion formed so as to have regular areas. 
     In addition, it is possible to manufacture a foldable battery cell using an electrode assembly including an electrode according to the present invention, and therefore it is possible to provide a battery cell usable in a device having a bent or curved shape. 
    
    
     
       DESCRIPTION OF DRAWINGS 
         FIG.  1    is a plan view of an electrode sheet according to an embodiment. 
         FIG.  2    is a plan view of an electrode sheet according to another embodiment. 
         FIG.  3    is a plan view showing a notching portion formed in the electrode sheet of  FIG.  1   . 
         FIG.  4    is a vertical sectional view of the electrode sheet of  FIG.  3   . 
     
    
    
     BEST MODE 
     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 means that such elements may be further included unless mentioned otherwise. 
     Embodiments of the present invention will be described in detail with reference to the accompanying drawings. 
       FIG.  1    is a plan view of an electrode sheet according to an embodiment. 
     Referring to  FIG.  1   , the electrode sheet  100  is taken out in an arrow direction, and  FIG.  1    shows a start part of the electrode sheet that is taken out. 
     An electrode manufacturing method according to the present invention includes a coating step of forming an electrode mixture coated portion on an electrode sheet so as to include an uncoated portion having no electrode mixture formed thereon by coating, a step of slitting the electrode sheet into a plurality of unit electrode sheets, and a step of notching the slit electrode sheet. 
     Referring to  FIG.  1   , an electrode mixture coated portion  110  is formed at the electrode sheet  100  while the electrode sheet is taken out in an arrow direction. At this time, the coated portion  110  is formed such that an uncoated portion having no electrode mixture formed thereon by coating is formed. 
     The coated portion  110  may be formed at any one of the upper surface and the lower surface of the electrode sheet or may be formed at opposite surfaces of the electrode sheet. 
     The uncoated portion includes an electrode tab formation portion  120  and a folding portion  130  formed so as to extend in a direction parallel to a direction in which the electrode sheet is taken out. 
     In the electrode sheet according to the present invention, the uncoated portion and the coated portion are continuously formed in the direction parallel to the direction in which the electrode sheet is taken out. 
     A slitting line  140  is formed at the middle of the electrode sheet  100  in the direction in which the electrode sheet is taken out, and the coated portion  110 , the electrode tab formation portion  120 , and the folding portion  130  are formed so as to be symmetrical with respect to the slitting line  140 . 
     The slitting line means a preliminary cutting line along which a cutter moves in order to divide the coated portion in the slitting step. 
     The slitting step is performed through a process of slitting a coated portion  110  located between a folding portion  130  and another folding portion  130  adjacent to the folding portion. At this time, in order to produce electrodes having uniform sizes, the slitting line  140  is set at a position at which the coated portion  110  is divided into two equal parts. 
     The folding portion  130  is an uncoated portion formed between the slitting line  140  and the electrode tab formation portion  120 . In the case in which a battery cell including an electrode assembly manufactured using unit electrodes formed through the slitting and notching steps is manufactured and then folded, the folding portion is set to be an uncoated portion having no electrode mixture formed thereon by coating in order to prevent the electrode mixture from being separated from an electrode current collector. 
     Meanwhile, in order to prevent a positive electrode tab and a negative electrode tab from contacting each other in a stacking direction when a positive electrode and a negative electrode formed through slitting and notching are stacked in the state in which a separator is interposed therebetween, the electrode tab may be formed so as to be biased to one side from the outer periphery of the electrode from which the electrode tab protrudes. As shown in  FIG.  1   , therefore, electrode tabs formed at opposite sides of the electrode tab formation portion  120  in the direction in which the electrode sheet is taken out are formed so as not to overlap. 
     The present invention relates to an electrode manufacturing method for manufacturing an electrode that is folded on the basis of an x-axis and an electrode sheet, wherein a first coated portion  110   a  and a second coated portion  110   b  are formed at opposite sides of a unit electrode  101  formed through slitting and notching on the basis of the folding portion  130 . 
     When the electrode is folded, the first coated portion  110   a  and the second coated portion  110   b  face each other, and therefore the first coated portion and the second coated portion may be formed so as to have the same size. 
       FIG.  2    is a plan view of an electrode sheet according to another embodiment. 
     Referring to  FIG.  2   , the electrode sheet  200  is taken out in an arrow direction, and  FIG.  2    shows a start part of the electrode sheet that is taken out. 
     Unlike the electrode sheet of  FIG.  1   , the electrode sheet of  FIG.  2    is configured to have a structure in which an electrode tab formation portion  220   a  is formed at each of opposite side ends of the electrode sheet  200  that is taken out and in which an electrode tab formation portion  220   b  is formed at a middle portion of the electrode sheet. 
     In addition, a coated portion  210 , a folding portion  230 , and a coated portion  210  are sequentially formed from the electrode tab formation portion  220   a  in an inward direction of the electrode sheet  200 . 
     That is, the coated portions  210  are formed on opposite sides of the folding portion  230 , and this form may be expressed as a coated portion  210  having a folding portion  230  formed at the middle thereof. 
     In addition, a coated portion  210  including a folding portion  230  is formed at each of the upper part and the lower part of the electrode sheet on the basis of the electrode tab formation portion  220   b  at the middle portion of the electrode sheet in the direction in which the electrode sheet is taken out. 
     The electrode sheet  200  has a structure in which the electrode sheet is slit along two slitting lines  240  to form three unit electrode sheets  251 ,  252 , and  253 . The unit electrode sheet  251  and the unit electrode sheet  253  have the same width, and the width of the unit electrode sheet  252  is formed so as to be greater than the width of each of the unit electrode sheets  251  and  253 . Consequently, in the structure in which the electrode tab formation portions are formed at opposite side ends and the middle portion of the electrode sheet, as in the electrode sheet  200 , unit electrode sheets having two kinds of widths are formed. 
     The slitting step is performed using a method of forming a slitting line  240  at the coated portion  210  located between the folding portions  230  and slitting the coated portion along the slitting line  240 . 
       FIG.  3    is a plan view showing a notching portion formed in the electrode sheet of  FIG.  1   . 
     Referring to  FIG.  3   , the notching step includes a notching process for forming an electrode tab  102  at the electrode tab formation portion  120  and a process of notching the electrode sheet along a notching line  122  in order to divide the electrode sheet into unit electrode sheets  150 . 
     The slitting line  140  that divides the electrode sheet  100  into a plurality of unit electrode sheets  150  is formed on the coated portion  110 , and the notching line  122  is formed so as to be perpendicular to the slitting line  140  and is formed in the shape of a straight line passing through the coated portion  110  and the folding portion  130 . 
     The notching process for forming the electrode tab and the process of notching the electrode sheet along the notching line may be sequentially performed. Alternatively, the notching process for forming the electrode tab and the process of notching the electrode sheet along the notching line may be simultaneously performed. 
     In the case in which the notching process for forming the electrode tab and the process of notching the electrode sheet along the notching line are simultaneously performed, it is possible to reduce an electrode manufacturing time. 
       FIG.  4    is a vertical sectional view of the electrode sheet of  FIG.  3   . 
     Referring to  FIG.  4   ,  FIG.  4    is a vertical sectional view of the electrode sheet cut in the x-axis of  FIG.  3   . 
     The uncoated portion may be formed such that the width W 1  of the electrode tab formation portion  120  and the width W 2  of the folding portion  130  are different from each other. For example, when considering a structure in which electrode tabs are not formed so as to overlap each other, the width W 1  of the electrode tab formation portion  120  may be formed so as to be less than the width W 2  of the folding portion  130 . Alternatively, the width W 1  of the electrode tab formation portion  120  may be formed so as to be greater than the width W 2  of the folding portion  130  depending on the sizes of the electrode tabs. 
     The folding portion  130  is disposed so as to face each other in the state in which the electrode is folded. It is preferable for the width W 2  of the folding portion  130  to be at least ½ of the circumference of a circle having the thickness H of the coated portion as a radius. Consequently, the width W 2  of the folding portion  130  may be formed so as to be greater than the thickness H of the coated portion x n. 
     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 
     
         
           100 ,  200 : Electrode sheets 
           101 : Unit electrode 
           102 : Electrode tab 
           110 ,  210 : Coated portions 
           110   a : First coated portion 
           110   b : Second coated portion 
           120 ,  220   a ,  220   b : Electrode tab formation portions 
           122 : Notching line 
           130 ,  230 : Folding portions 
           140 ,  240 : Slitting lines 
           150 ,  251 ,  252 ,  253 : Unit electrode sheets 
         H: Thickness of coated portion 
         W 1 : Width of electrode tab formation portion 
         W 2 : Width of folding portion 
       
    
     INDUSTRIAL APPLICABILITY 
     As is apparent from the above description, in an electrode manufacturing method according to the present invention, in order to form not only an uncoated portion, which is an electrode tab formation portion, but also an uncoated portion, which is configured to manufacture a folded electrode, on an electrode sheet, a method of coating a portion of the electrode sheet with an electrode mixture is used, whereby it is possible to reduce the number of manufacturing steps as compared to a method of coating the entirety of the electrode sheet with the electrode mixture and then removing the coating and to reduce defects that may occur during a coating removal process. 
     Also, in a notching process for manufacturing a unit electrode, notching is performed such that a folding portion is included in the unit electrode, whereby it is possible to obtain a unit electrode having a coated portion and an uncoated portion formed so as to have regular areas. 
     Also, it is possible to manufacture a foldable battery cell using an electrode assembly including an electrode according to the present invention, and therefore it is possible to provide a battery cell usable in a device having a bent or curved shape.