Method for manufacturing electrode assembly

Abstract

The present invention provides a method for manufacturing an electrode assembly, comprising: a step (S10) of alternately arranging positive electrodes and negative electrodes on a separator folded in a zigzag shape to form a laminate in which the positive electrodes, the separator, and the negative electrodes are alternately arranged; a step (S20) of applying pressure to the laminate to fix the positions of the positive electrode and the negative electrode with respect to the separator; a step (S30) for applying heat and pressure to the laminate to bond the positive electrode, the separator, and the negative electrode; and a step (S40) of cutting a side surface of the laminated body to form an electrode assembly, in which the side surface includes the bent portion.

Description

Technical Field

[0001] This application claims the benefit of the filing date of Korean Patent Application No. 10-2022-0098947 filed in the Korean Intellectual Property Office on August 9, 2022, the entire contents of which are incorporated herein by reference.

[0002] The present invention relates to a method for manufacturing an electrode assembly including a zigzag separator and a method for improving electrolyte wetting of the electrode assembly. Background Art

[0003] Electrochemical devices use electrochemical reactions to convert chemical energy into electrical energy. In recent years, lithium secondary batteries with high energy density and voltage, long cycle life and can be used in a variety of fields have been widely used. In recent years, as the demand for electric vehicles and energy storage devices has increased, materials and structures are being developed to maximize capacity and energy density.

[0004] A secondary battery may include an electrode assembly, the electrode assembly including a positive electrode, a negative electrode, and a separator disposed between the positive electrode and the negative electrode, and the electrode assembly may be contained in a shell together with an electrolyte to manufacture a secondary battery. Depending on the shape of the shell containing the electrode assembly, the secondary battery may be classified into a pouch type, a cylindrical type, a prismatic type, a coin type, etc., and depending on the manufacturing method or shape of the electrode assembly, the secondary battery may be classified into a jelly roll type, a stacked type, etc.

[0005] The stacked electrode assembly is manufactured by stacking a plurality of positive electrodes, separators and negative electrodes prepared in a predetermined size, but the transfer of each electrode and separator is cumbersome, and it is difficult to maintain a predetermined arrangement when stacking, resulting in low productivity. Therefore, a Z-shaped stacked electrode assembly has been developed, in which a long sheet-shaped separator is bent into a Z-shaped form, and the positive and negative electrodes are alternately arranged between adjacent bends. For example, a Z-shaped electrode assembly can be manufactured by tilting or swinging the workbench of the stacked electrode assembly when supplying a long sheet-shaped separator wound on a cylinder, or by reciprocating the supply roller for transferring the separator to fold the separator in a Z-shape and arrange each electrode therebetween. Compared with the prior art, the Z-shaped stacking process is simple, the productivity is excellent, and the stacking structure can be stably maintained even if the bonding force of the separator is relatively low or non-existent.

[0006] Typically, when stacked in a Z-shape, the diaphragm is folded at a predetermined interval to form a curved portion, so that the interval is larger than the width of the positive electrode and the negative electrode to ensure a surplus space. Therefore, the Z-shaped electrode assembly includes an area on both sides where only the curved portion formed by the diaphragm is stacked, in which there is an empty space compared to the area where the electrode and the diaphragm are stacked together and is not fixed, so there is a problem of folding or shaking, making it difficult to insert the electrode assembly into the housing or bag. In order to solve this problem, heat and pressure are applied to the curved portion to join the curved portion and / or adjacent curved portions. However, during the process of membrane bonding, the pores formed in the diaphragm are closed, resulting in reduced permeability, increased resistance, and reduced wettability of the electrolyte. Summary of the invention

[0007] Technical issues

[0008] An object of the present invention is to provide a method for manufacturing a zigzag electrode assembly having a structure with excellent insertability into a case or a bag due to the absence of folding or shaking of a bent portion of a separator and excellent wettability of the separator to an electrolyte.

[0009] Solution

[0010] One aspect of the present invention provides a method for manufacturing an electrode assembly, comprising: a step (S10) of alternately arranging positive electrodes and negative electrodes on a separator folded in a Z-shape to form a bent portion to form a stack in which positive electrodes, separators, and negative electrodes are alternately arranged; a step (S20) of applying heat and pressure to the stack to fix the positions of the positive electrodes and the negative electrodes relative to the separator; a step (S30) of applying heat and pressure to the stack to bond the positive electrodes, the separator, and the negative electrodes; and a step (S40) of cutting the side of the stack to form an electrode assembly, wherein the side includes the bent portion.

[0011] In the method of manufacturing the electrode assembly, a length of the negative electrode in a width direction may be 1 to 10% longer than a length of the positive electrode in the width direction.

[0012] The method for manufacturing the electrode assembly may further include a step ( S11 ) of surrounding an outer peripheral surface of the stacked body formed in the step ( S10 ) with an end portion of the separator.

[0013] In the method for manufacturing the electrode assembly, in the step ( S20 ), a pressure of 1 to 6 MPa may be applied to the laminate at a temperature of 50 to 60° C. for 1 to 60 seconds.

[0014] In the method for manufacturing the electrode assembly, in the step ( S20 ), the positive electrode and the separator, and the separator and the negative electrode may be partially bonded to fix the positions of the positive electrode and the negative electrode relative to the separator.

[0015] In the method for manufacturing the electrode assembly, in the step ( S30 ), a pressure of 1 to 6 MPa may be applied to the laminate at a temperature of 50 to 60° C. for 1 to 60 seconds.

[0016] In the method for manufacturing the electrode assembly, in the step ( S30 ), the positive electrode and the separator, and the separator and the negative electrode may be completely bonded.

[0017] In the method for manufacturing the electrode assembly, the side surface may be formed of a separator including the bent portion, and the electrode assembly may not include the bent portion.

[0018] In the method for manufacturing the electrode assembly, the bent portion may extend parallel to a length direction of the separator.

[0019] In the method of manufacturing the electrode assembly, an interval between the bent portion and the negative electrode may be smaller than an interval between the bent portion and the positive electrode.

[0020] In the method for manufacturing the electrode assembly, a length of the negative electrode in a width direction may be 10 to 15 times a distance between the bent portion and the negative electrode.

[0021] In the method for manufacturing the electrode assembly, in the step (S40), the side surface may be cut in parallel with a height direction of the electrode assembly.

[0022] In the manufacturing method of the electrode assembly, in the step (S40), the cutting position between the negative electrode and the bent portion may be cut, and the ratio of the interval between the cutting position and the negative electrode and the interval between the cutting position and the bent portion is 1:8 to 1:10.

[0023] In the method for manufacturing the electrode assembly, the interval between the end of the separator and the positive electrode in the electrode assembly may be 1.5 to 2 times the interval between the end of the separator and the negative electrode.

[0024] Another aspect of the present invention provides an electrode assembly manufactured by the method for manufacturing the electrode assembly.

[0025] Beneficial effects

[0026] The manufacturing method of the present invention provides an electrode assembly that is excellent in productivity and has a structure in which a separator does not fold or shake, thereby being able to improve productivity of an electrochemical device including the electrode assembly.

[0027] In addition, the electrode assembly manufactured by the manufacturing method of the present invention can allow the electrolyte to be uniformly impregnated into the separator, thereby preventing or minimizing the deposition of lithium in the separator in a dendrite-like form. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 is a conceptual diagram illustrating a step of applying pressure to a stacked body to fix positions of positive and negative electrodes relative to a separator in a process of manufacturing an electrode assembly according to an embodiment of the present invention.

[0029] Figure 2 is a conceptual diagram illustrating a step of applying heat and pressure to a stacked body to bond a positive electrode, a separator, and a negative electrode in a process of manufacturing an electrode assembly according to an embodiment of the present invention.

[0030] Figure 3 is a conceptual diagram showing a cross section of a stacked body in a conventional electrode assembly manufacturing process.

[0031] Figure 4 is a conceptual diagram illustrating a cross section of a stacked body in a process of manufacturing an electrode assembly according to an embodiment of the present invention.

[0032] Figure 5 is a conceptual diagram illustrating a cross section of a stacked body in a process of manufacturing an electrode assembly according to an embodiment of the present invention.

[0033] Figure 6 is a conceptual diagram showing a cross section of an electrode assembly according to an embodiment of the present invention. DETAILED DESCRIPTION

[0034] In order to enable ordinary technicians in the technical field to which the present invention belongs to easily implement the present invention, the various structures of the present invention are described in detail below, but this is only an example, and the scope of rights of the present invention is not limited by the following content.

[0035] The term "comprising" used in this specification is used to list materials, compositions, devices and methods useful for the present invention, and is not limited to the listed examples.

[0036] The terms “approximately” and “substantially” as used in this specification are used in the sense of a range of numerical values ​​or degrees or close to such a range in consideration of inherent manufacturing and material tolerance errors, and are used to prevent the disclosure content mentioned in the accurate or absolute numerical values ​​provided to facilitate understanding of the present invention from being illegally used by infringers.

[0037] The "electrochemical device" used in this specification may refer to a primary battery, a secondary battery, a supercapacitor, etc. The electrochemical device may be a lithium ion secondary battery, and may be a pouch type, a cylindrical type, a prismatic type, or a coin type, but the specific shape is not limited thereto.

[0038] The "diaphragm" used in this specification refers to a functional diaphragm having a porous coating layer containing an inorganic substance and a binder formed on at least one side of a porous substrate such as a polyolefin substrate or a nonwoven fabric, but is not limited thereto. The diaphragm can generally refer to an independent diaphragm formed of an inorganic substance and a binder without a porous substrate or a diaphragm formed of a porous substrate without a porous coating layer.

[0039] The "electrode" used in this specification generally refers to a "positive electrode" and a "negative electrode", and may refer to coating an electrode active material on at least one side of a material having conductivity without causing a chemical change in an electrochemical device, and drying the same. The types of the material and the electrode active material are not limited as long as they can be used in an electrochemical device.

[0040] The "interval" used in this specification refers to the shortest distance between designated positions.

[0041] Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. In order to explain or emphasize the contents of the embodiments of the present invention, the accompanying drawings may be exaggerated, omitted or simplified.

[0042] An embodiment of the present invention provides a method for manufacturing an electrode assembly, the method comprising: a step (S10) of alternately arranging a positive electrode and a negative electrode on a separator folded in a zigzag shape to form a curved portion to form a stacked body in which positive electrodes, separators, and negative electrodes are alternately arranged; a step (S20) of applying heat and pressure to the stacked body to fix the positions of the positive electrodes and negative electrodes relative to the separator; a step (S30) of applying heat and pressure to the stacked body to bond the positive electrodes, the separators, and the negative electrodes; and a step (S40) of cutting a side surface of the stacked body to form an electrode assembly. At this time, the side surface includes the curved portion.

[0043] The step (S10) is a step of folding the separator in a zigzag shape to form a curved portion, and alternately arranging positive electrodes and negative electrodes on the separator having the curved portion to form a laminated body in which positive electrodes, separators, and negative electrodes are alternately arranged.

[0044] In the step (S10), the length of the separator in the longitudinal direction (or MD direction) may be greater than the length in the width direction (or TD direction). The separator may be bent in a zigzag shape at predetermined intervals along the MD direction to form the bent portion. For example, the bent portion may extend parallel to the TD direction edge of the separator. The predetermined intervals may be the same or different from each other, but are preferably the same as each other, and may be set to be longer than the length in the width direction of the positive electrode or the negative electrode.

[0045] The separator, the positive electrode and the negative electrode may each be in a rectangular shape, but are not limited thereto. For example, the separator, the positive electrode and the negative electrode may each be in a rectangular shape whose length in the MD direction is longer than that in the TD direction. A plurality of the positive electrodes and the negative electrodes may be arranged along the MD direction of the separator, and the MD direction of the separator and the TD direction of the positive electrode and the negative electrode may be arranged parallel to each other. The number of the positive electrode and the negative electrode may be determined according to the capacity required by the electrochemical device finally manufactured.

[0046] The length of the positive electrode in the MD direction may be the same as the length of the negative electrode in the MD direction. Based on the length WC of the positive electrode in the TD direction, the length WA of the negative electrode in the TD direction may be 1 to 10% longer than the length WC of the positive electrode in the TD direction. When less than the range, as the electrochemical device is repeatedly used, the problem of dendritic deposition of lithium on the surface of the negative electrode may occur. When exceeding the range, the effect of preventing lithium deposition is no longer improved, and the problem of difficulty in the predetermined arrangement of the electrodes in the electrode assembly may occur.

[0047] The positive electrode and the negative electrode may be alternately arranged between mutually adjacent curved portions formed on the separator. Thus, the stack may include a structure in which the positive electrode and the negative electrode are repeatedly arranged with the separator interposed therebetween. Preferably, the positive electrode and the negative electrode may be aligned in such a manner that their center lines in the TD direction are consistent.

[0048] After the step ( S10 ), the method may further include a step ( S11 ) of surrounding the outer peripheral surface of the stacked body formed in the step ( S10 ) with the end portion of the separator.

[0049] The length of the separator in the MD direction may be greater than that in the TD direction, and the separator may be bent in a zigzag shape at predetermined intervals along the MD direction to form a plurality of bent portions, and the end portions of the separator may be extended without being bent. Figures 3 to 5The end 15 of the diaphragm may surround the outer peripheral surface of the stack 10 more than once, and the interface between the electrodes 13 and 14 constituting the stack 10 and the diaphragm 11 may be compressed by the pressure surrounded by the end 15, so that the stable contact between the electrodes and the diaphragm may be maintained. For example, the end 15 of the diaphragm may surround the curved portions 12 located on both sides of the stack.

[0050] The step ( S20 ) is a step of applying pressure to the stacked body formed in the step ( S10 ) to fix the positions of the positive electrode and the negative electrode relative to the separator. Figure 1 is a conceptual diagram illustrating the step ( S20 ) in the method for manufacturing an electrode assembly according to an embodiment of the present invention.

[0051] Reference Figure 1 , the step (S20) may be performed using a first pressure device 100. The first pressure device 100 may partially pressurize the stack 10 to fix the relative position of the aligned electrodes in the stack 10 relative to the diaphragm. The first pressure device 100 may include a pressurizing plate 110 for pressurizing the stack 10 and a fixing portion 120 for clamping the stack 10 while the pressurizing plate 110 presses the stack 10.

[0052] The stack 10 includes a structure in which positive electrodes, separators and negative electrodes are alternately stacked through the step (S10) or the step (S11), but the position of the positive electrode or the negative electrode relative to the separator is not completely fixed. The stack 10 can be arranged between upper and lower pressure plates 110 in a state of being clamped by one or more clamps 121 provided on the fixing portion 120. The pressure plate 110 is provided with a groove 111 at a position corresponding to the clamp 121, so that the clamp 121 is not pressurized, but only the stack 10 fixed to the clamp 121 is pressurized. The first pressure device 100 can make the separator and the electrode stacked on the remaining part of the stack 10 other than the part clamped by the clamp 121 bond to each other. The shape and number of the pressure plate 110, the clamp 121, etc. are not limited to Figure 1 Shapes and quantities shown.

[0053] In the step (S20), a pressure of 1 to 6 MPa may be applied to the stack 10 at a temperature of 50 to 100°C for 1 second to 30 minutes. Preferably, in the step (S20), a pressure of 1 to 6 MPa may be applied to the stack 10 at a temperature of 50 to 60°C for 1 second to 60 seconds. In the step (S20), partial bonding between the separator and the electrode is induced in the stack 10 to fix the position of the electrode relative to the separator. Preferably, in the step (S20), the electrode may be fixed so that it does not move in a state where the center line of the length in the TD direction of the electrode coincides with the center line of the interval between the adjacent curved portions of the separator. When the temperature and pressure are within the range, the bonding force between the separator and the electrode after the step (S20) may be 5 gf / 20 mm or more. The position of the electrode relative to the separator may be fixed within the bonding force range. When the pressure is less than 1 MPa, the position of the electrode may not be fixed, and the electrode may be separated from the predetermined position during the handling of the stack 10. When the pressure exceeds 6 MPa, the active material layer formed on the electrode may be damaged, or the pore structure formed on the separator may be broken, resulting in problems with the air permeability and resistance of the separator.

[0054] The laminated body 10 pressurized in the step ( S20 ) may be removed from the first press device 100 by the clamp 121 and transferred to the second press device 200 .

[0055] The step ( S30 ) is a step of applying heat and pressure to the laminated body 10 pressurized in the step ( S20 ) to bond the positive electrode, the separator, and the negative electrode. Figure 2 is a conceptual diagram illustrating the step ( S30 ) in the method for manufacturing an electrode assembly according to an embodiment of the present invention.

[0056] Reference Figure 2 , the step (S30) can be performed using the second pressure device 200. The second pressure device 200 can pressurize the entire two sides of the stack 10 to bond the separator and the electrode included in the stack 10 to each other. Specifically, the two sides of the stack 10 are surfaces that do not include the bent portion of the separator, and refer to the surfaces where the electrodes and the separators are alternately stacked. In the step (S30), heat and pressure are applied to the stack 10 to bond the positive electrode and the separator, and the separator and the negative electrode, which are stacked adjacent to each other, to each other.

[0057] Reference Figure 2The step (S30) may be performed using a second pressure device 200. The second pressure device 200 may heat-press both sides of the stack 10 to bond the separator and the electrode included in the stack 10. The second pressure device 200 may include a pressurizing plate 210 that heat-presses the stack 10.

[0058] The stack 10 is subjected to the step (S20) so that the electrode and the diaphragm are partially bonded to fix the position of the electrode relative to the diaphragm, but the diaphragm and the electrode are not completely bonded to each other. The stack 10 can be arranged between upper and lower pressure plates 210, and the pressure plates 210 can perform heat pressing on both sides of the stack 10. The second pressure device 200 can perform heat pressing on both sides of the stack 10 including the portion that was clamped by the clamp 121 in the previous step and not pressurized, so that the diaphragm and the electrode are bonded to each other. The shape and number of the pressure plates 210 are not limited to Figure 2 Shapes and quantities shown.

[0059] In the step (S30), a pressure of 1 to 6 MPa may be applied to the stack 10 at a temperature of 50 to 100°C for 1 second to 30 minutes. Preferably, in the step (S30), a pressure of 1 to 6 MPa may be applied to the stack 10 at a temperature of 50 to 60°C for 1 second to 60 seconds. More preferably, in the step (S30), a temperature and pressure higher than that of the step (S20) may be applied. In the step (S30), the positive electrode in the stack 10 is completely bonded to the diaphragm, and the diaphragm is completely bonded to the negative electrode. When the pressure is less than 1 MPa, during the manufacturing process and use of the electrochemical device, the electrode may be separated from the diaphragm and a short circuit caused by electrode contact may occur. When the pressure exceeds 6 MPa, the active material layer formed on the electrode may be destroyed, or the pore structure formed on the diaphragm may be broken, resulting in problems with the air permeability and resistance of the diaphragm.

[0060] The laminated body 10 hot-pressed in the step ( S30 ) may be processed into an electrode assembly through a subsequent process after being removed from the second press device 200 .

[0061] The step ( S40 ) is a step of cutting the side surface of the laminated body 10 that is heat-pressed in the step ( S30 ) to form an electrode assembly. Figures 3 to 5 It is shown in Figure 2 1 is a conceptual diagram of a cross section of the laminate 10 after the step (S30) as viewed from direction A. The length of the laminate 10 in the MD direction may be greater than the length in the TD direction, and the A direction may be a direction parallel to the MD direction of the laminate 10.

[0062] Figure 31 is a conceptual diagram showing a process of applying heat and pressure to a region where the separators are stacked in order to solve the folding or shaking problem of the conventional separators.

[0063] Reference Figure 3 , the stack 10 for forming a Z-shaped electrode assembly has a structure in which the positive electrode 13 and the negative electrode 14 are alternately arranged with the separator 11 therebetween, and the separator 11 may include one or more bends 12 formed by folding in a Z shape. For example, the length WA of the negative electrode 14 in the TD direction may be greater than the length WC of the positive electrode 13 in the TD direction, and the length of the stack 10 in the TD direction may be composed of the length WA of the negative electrode 14 in the TD direction and the length WS of the portion consisting only of the separator 11. The portion consisting only of the separator 11 may have a structure in which the separator 11 including the bend 12 is stacked in the height direction Z of the stack 10, and a hollow space may be included because no electrode is arranged. If the stack 10 is directly inserted into the housing, it is possible that the portion consisting only of the separator 11 is inserted in a folded state, or the separator 11 vibrates and causes the separator 11 to tear. In the prior art, heat and pressure (P) are applied to the portion consisting only of the separator 11 in the vertical direction (in the direction parallel to the Z direction) to bond the adjacent separators 11, thereby increasing the strength of the separator 11 corresponding to the length WS and preventing folding or shaking. However, during the bonding process between the separators 11, the pore structure formed in the separator 11 is destroyed, so there is a problem that the air permeability is reduced and the separator 11 cannot be well impregnated with the electrolyte.

[0064] Figure 4 and Figure 5 As a solution Figure 3 A means for illustrating the problem of the prior art is to illustrate a conceptual diagram of the step (S40), Figure 6 is a conceptual diagram showing the electrode assembly 20 .

[0065] Reference Figures 4 to 6 The step (S40) is a step of removing at least one side surface of the stacked body 10 by cutting the separator 11 along a predetermined position C on the separator 11 in the stacked body 10. The side surface may include a bent portion 12. Preferably, in the step (S40), both side surfaces of the stacked body 10 may be cut. The electrode assembly 20 formed in the step (S40) may not include the bent portion 12.

[0066] The cutting may be performed by press cutting, laser, hot wire, etc. Preferably, in the step (S40), the blade may be cut along a direction parallel to the height direction (Z direction) of the stacked body 10, and the direction may be parallel to the height direction of the electrode assembly 20. During the cutting, only the separator 11 may be cut while the portion where the electrodes are stacked and the side surface including the bent portion 12 are fixed.

[0067] An embodiment of the present invention provides an electrode assembly 20 having the following structure, which can ensure the advantages of the existing manufacturing of Z-shaped electrode assemblies while preventing the folding or shaking of the diaphragm 11 by determining the relationship between the length of the diaphragm in the TD direction and the length of the electrode in the TD direction and the specific position of the cutting position C.

[0068] Specifically, in the laminate 10, the interval WAS between the bent portion 12 and the negative electrode 14 may be smaller than the interval WCS between the bent portion 12 and the positive electrode 13. The cutting position C is located between the bent portion 12 and the negative electrode 14, and the separator 11 having a predetermined length from the positive electrode 13 and the negative electrode 14 is retained by cutting.

[0069] Specifically, the length WA of the negative electrode 14 in the TD direction may be 10 to 15 times the interval WAS between the bend 12 and the negative electrode 14. When the length WA of the negative electrode 14 in the TD direction is less than 10 times the interval WAS between the bend 12 and the negative electrode 14, at least a portion of the separator 11 may be folded toward the electrode direction during the cutting process. When the length WA of the negative electrode 14 in the TD direction exceeds 15 times the interval WAS between the bend 12 and the negative electrode 14, the separator 11 may be torn during the cutting process.

[0070] Specifically, in the step (S40), the cutting position C between the negative electrode 14 and the curved portion 12 is cut, and the ratio of the interval W1 between the cutting position C and the negative electrode 14 and the interval W2 between the cutting position C and the curved portion 12 can be 1:8 to 1:10. When the W1:W2 is less than 1:8, at least a portion of the separator 11 will be folded toward the electrode during the cutting process. When the W1:W2 is greater than 1:10, the separator 11 will be torn during the cutting process.

[0071] In the electrode assembly 20 formed by cutting according to the step (S40), the interval between the end (point C) of the separator 11 and the positive electrode 13 may be 1.5 to 2 times the interval between the end of the separator 11 and the negative electrode 14. Even if the sizes of the positive electrode 13 and the negative electrode 14 are changed, the ratio is preferably kept constant.

[0072] Another embodiment of the present invention provides an electrode assembly manufactured by the method according to the embodiment and an electrochemical device including the electrode assembly.

[0073] The electrode assembly is formed by cutting the side surface, and since the bent portion of the separator is not included, the appearance is similar to that of a conventional stacked electrode assembly. However, in a stacked (L&S) electrode assembly, since there is no step of fixing the electrode position relative to the separator, the electrodes cannot be aligned during the rapid stacking of the separator and the electrode, and uniform bonding between the separator and the electrode cannot be achieved.

[0074] Therefore, the electrode assembly according to the embodiment of the present invention can provide an aligned electrode arrangement and uniform electrode bonding compared to the existing stacked electrode assembly, and can prevent folding or shaking of the separator to reduce defects when inserted into the case.

[0075] The shape of the housing or bag for inserting the electrode assembly is not limited. For example, the electrochemical device can be a cylindrical, prismatic, coin-shaped or pouch-shaped lithium secondary battery. The lithium secondary battery can be grouped or modularized as a unit cell for use in electric vehicles (BEVs), hybrid electric vehicles (HEVs), plug-in hybrid electric vehicles (PHEVs), power storage devices, etc.

[0076] The present invention is described in more detail below through specific examples and experimental examples. The following examples and experimental examples are only used to illustrate the present invention, and the present invention is not limited to the following examples and experimental examples.

[0077] Example 1

[0078] A 15 μm thick separator coated with a slurry containing an inorganic substance and a binder was prepared, and 30 and 31 positive electrodes of 90 mm × 315 mm and negative electrodes of 95.5 mm × 320 mm were prepared, respectively. The separator was folded 20 times in a zigzag shape at intervals of 98.5 mm and the ends were left, and the positive and negative electrodes were arranged in sequence while the separator was folded, thereby preparing a laminate. In the laminate, the interval between the negative electrode and the bent portion of the separator was 30 mm, and the interval between the positive electrode and the bent portion was 32.75 mm. The laminate was surrounded by the ends of the separator.

[0079] The laminate was placed in a first press device and pressurized at 60° C. and 2 MPa for 1 minute. Then, the laminate was placed in a second press device and heat-pressed at 70° C. and 3 MPa for 30 seconds.

[0080] In the interval WAS between the negative electrode and the bent portion, the position where the interval W1 from the negative electrode to the cutting position C and the interval W2 from the cutting position C to the bent portion are 1:9 is used as the cutting position C, and the two side surfaces of the stack are cut by press cutting to manufacture an electrode assembly in which the interval W1 between the negative electrode and the separator is 3 mm.

[0081] Comparative Example 1

[0082] The same types and quantities of separators, positive electrodes, and negative electrodes as those used in Example 1 were used, and the laminate was pressed and hot-pressed in the same manner.

[0083] Reference Figure 3 The portion WS of both sides of the stacked body where only the separators were stacked was hot pressed at 120° C. for 20 seconds in the upper and lower directions to manufacture an electrode assembly.

[0084] Comparative Example 2

[0085] Using the same kind of separator, positive electrode, and negative electrode as used in Example 1, 61 separators having a size of 100 mm×380 mm were prepared, and the positive electrode, the separator, and the negative electrode were stacked in this order to form a stacked body.

[0086] Both surfaces of the stack were hot-pressed at 60° C., a pressure of 18 kgf / cm, and a speed of 220 cpm to produce an electrode assembly.

[0087] Comparative Example 3

[0088] The electrode assembly is manufactured in the same manner as in Example 1, except that the interval WAS between the negative electrode and the curved portion is set as the cutting position C, where the interval W1 from the negative electrode to the cutting position C and the interval W2 from the cutting position C to the curved portion are 1:7, and the two side surfaces of the stack are cut by press cutting so that the interval between the negative electrode and the separator is 3.75 mm.

[0089] Comparative Example 4

[0090] The electrode assembly is manufactured in the same manner as in Example 1, except that the interval WAS between the negative electrode and the curved portion is set as the cutting position C, where the interval W1 from the negative electrode to the cutting position C and the interval W2 from the cutting position C to the curved portion are 1:11, and the two side surfaces of the stack are cut by press cutting so that the interval between the negative electrode and the separator is 2.5 mm.

[0091] Experimental Example 1. Confirmation of the state of the separator in the long side of the electrode assembly

[0092] Electrode assemblies were prepared according to Example 1 and Comparative Examples 1 to 6, and the state of the separator included in each electrode assembly was confirmed with the naked eye. Then, the electrode assembly was completely inserted into the bag, and then taken out again and the state of the separator was confirmed with the naked eye, and the results (○: intact, △: separator folded, ×: separator torn) were sorted in the following Table 1.

[0093] [Table 1]

[0094] Diaphragm status just after manufacturing Diaphragm status after insertion into bag Comparative Example 1 ○ ○ Comparative Example 2 △ △ Comparative Example 3 △ × Comparative Example 4 × × Example 1 ○ ○

[0095] As shown in Table 1 above, the electrode assembly of Comparative Example 2, which is a stacked electrode assembly, was confirmed to have folded edges in the MD direction of the separator immediately after manufacture. In Example 1 and Comparative Example 1, in which a process for preventing the separator from folding was added to the Z-shaped electrode assembly, the separator was also intact immediately after manufacture and after insertion into the bag.

[0096] However, in Comparative Examples 3 to 6 in which the values ​​of the separator and the negative electrode were adjusted to be different from those of the examples of the present invention and cut, the separator was folded during the cutting process, or the folded separator was torn when inserted into the bag.

[0097] Experimental Example 2: Confirmation of the wettability of the separator to the electrolyte

[0098] Electrode assemblies were manufactured according to Example 1 and Comparative Examples 1 to 6, and then each electrode assembly was completely inserted into a bag. 156 g of electrolyte (weight ratio of EC to EMC = 3:7) was injected into the bag, and the bag was vacuum-sealed.

[0099] The bag was placed at room temperature for 72 hours, and then the electrode assembly was taken out and disassembled to confirm the electrode and separator interface, and the time (hr) that all separator interfaces were immersed in the electrolyte was confirmed and organized in the following Table 2.

[0100] [Table 2]

[0101] Wettability (hr) Comparative Example 1 >72 Comparative Example 2 23 Comparative Example 3 21 Comparative Example 4 22 Example 1 20

[0102] As shown in Table 2 above, in Comparative Example 1 in which both sides of the electrode assembly including the bent portion of the separator were hot pressed, the entire separator interface was not uniformly impregnated even after 72 hours.

[0103] [Explanation of Reference Numerals]

[0104] 10: Laminated body 11: Separator

[0105] 12: Bend 13: Positive electrode

[0106] 14: Negative electrode 15: Diaphragm end

[0107] 20: Electrode assembly

[0108] 100: first pressure device 110: pressure plate

[0109] 111: groove 120: fixing part

[0110] 121: Clamp 200: Second pressure device

[0111] 210: Pressure plate

[0112] WA: Length of the negative electrode in the TD direction WC: Length of the positive electrode in the TD direction

[0113] WAS: The distance between the negative electrode and the curved part WCS: The distance between the positive electrode and the curved part

[0114] C: Cutting position

[0115] W1: The distance between the cutting position and the negative electrode

[0116] W2: The distance between the cutting position and the bending part

Claims

1. A method for manufacturing an electrode assembly, comprising: A step (S10) of alternately arranging positive electrodes and negative electrodes on a separator folded in a zigzag shape to form a bent portion to form a stacked body in which positive electrodes, separators, and negative electrodes are alternately arranged; applying heat and pressure to the stacked body to fix the positions of the positive electrode and the negative electrode relative to the separator (S20); applying heat and pressure to the laminate to bond the positive electrode, the separator, and the negative electrode (S30); as well as a step (S40) of cutting the side surface of the stacked body to form an electrode assembly, Wherein, the side surface includes the bent portion.

2. The method for manufacturing an electrode assembly according to claim 1, wherein: The length of the negative electrode in the width direction is 1 to 10% longer than the length of the positive electrode in the width direction.

3. The method for manufacturing an electrode assembly according to claim 1, wherein: The method further includes a step ( S11 ) of surrounding the outer peripheral surface of the stacked body formed in the step ( S10 ) with the end portion of the separator.

4. The method for manufacturing an electrode assembly according to claim 1, wherein: In the step (S20), a pressure of 1 to 6 MPa is applied to the laminate at a temperature of 50 to 60°C for 1 to 60 seconds.

5. The method for manufacturing an electrode assembly according to claim 4, wherein: In the step ( S20 ), the positive electrode and the separator, and the separator and the negative electrode are partially bonded to fix the positions of the positive electrode and the negative electrode relative to the separator.

6. The method for manufacturing an electrode assembly according to claim 1, wherein: In the step (S30), a pressure of 1 to 6 MPa is applied to the laminate at a temperature of 50 to 60°C for 1 to 60 seconds.

7. The method for manufacturing an electrode assembly according to claim 6, wherein: In the step (S30), the positive electrode and the separator, and the separator and the negative electrode are completely bonded.

8. The method for manufacturing an electrode assembly according to claim 1, wherein: The side surface is formed by a separator including the bent portion, and the electrode assembly does not include the bent portion.

9. The method for manufacturing an electrode assembly according to claim 1, wherein: The bent portion extends parallel to the length direction of the diaphragm.

10. The method for manufacturing an electrode assembly according to claim 9, wherein: The interval between the bent portion and the negative electrode is smaller than the interval between the bent portion and the positive electrode.

11. The method for manufacturing an electrode assembly according to claim 9, wherein: The length of the negative electrode in the width direction is 10 to 15 times the distance between the bent portion and the negative electrode.

12. The method for manufacturing an electrode assembly according to claim 9, wherein: In the step (S40), the side surface is cut in parallel with the height direction of the electrode assembly.

13. The method for manufacturing an electrode assembly according to claim 12, wherein: In the step (S40), a cutting position between the negative electrode and the bent portion is cut, wherein a ratio of an interval between the cutting position and the negative electrode and an interval between the cutting position and the bent portion is 1:8 to 1:

10.

14. The method for manufacturing an electrode assembly according to claim 12, wherein: In the electrode assembly, a spacing between an end of the separator and the positive electrode is 1.5 to 2 times a spacing between an end of the separator and the negative electrode. 15 . An electrode assembly, the electrode assembly being manufactured by the method according to claim 1 .

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