Method of manufacturing secondary battery and pouch for secondary battery

Abstract

The present invention relates to a method of manufacturing a secondary battery. The method of manufacturing a secondary battery according to the present invention includes a forming step of forming a pouch by pressing the pouch using a press mold such that a left accommodation groove and a right accommodation groove, which are symmetrical to each other and open upward, and a bridge connecting the left accommodation groove and the right accommodation groove to each other are formed in the pouch to accommodate an electrode assembly; and a folding step of placing the electrode assembly in one of the left accommodation groove and the right accommodation groove, and folding the pouch such that the left accommodation groove and the right accommodation groove face each other, wherein, in the forming step, the pouch is formed such that the bridge protrudes upward with respect to bottom surfaces of the left accommodation groove and the right accommodation groove, and a curved portion having a circular arc shape is formed at an upper end of the bridge.

Description

[0001] This application is a divisional application of the invention patent application with application number 201980005760.2.

[0002] This application claims priority to Korean Patent Application No. 10-2018-0028018, filed on March 9, 2018, the entire contents of which are incorporated herein by reference. Technical Field

[0003] This invention relates to a method for manufacturing secondary batteries and a bag for secondary batteries. Background Technology

[0004] Unlike primary batteries, secondary batteries are rechargeable and have a high potential for small size and large capacity. Therefore, much research is currently underway on rechargeable batteries. With technological advancements and increasing demands for mobile devices, the need for rechargeable batteries as an energy source is rapidly growing.

[0005] Rechargeable batteries are classified into coin-shaped batteries, cylindrical batteries, prismatic batteries, and pouch batteries based on the shape of their casings. In these secondary batteries, the electrode assembly installed in the casing is a rechargeable and dischargeable power generating device, featuring a structure with stacked electrodes and separators.

[0006] Electrode assemblies can be broadly classified into jelly roll type electrode assemblies, stacked type electrode assemblies, and stacked / folded type electrode assemblies. In a jelly roll type electrode assembly, a separator is inserted between the positive and negative electrodes. Each positive and negative electrode is provided in the form of a sheet coated with active material, and then the positive electrode, separator, and negative electrode are wound together. In a stacked type electrode assembly, multiple positive and negative electrodes and the separator between them are stacked sequentially. In a stacked / folded type electrode assembly, a stacked cell is wound together with a separator having a relatively long length.

[0007] Recently, pouch cells, which incorporate stacked / folded electrode assemblies in pouch cell cases made of aluminum laminates, have attracted widespread attention due to their low manufacturing cost, light weight, and ease of deformation, and their usage is gradually increasing.

[0008] However, when folding the bag that houses the electrode components to manufacture a secondary battery, bat-ear-shaped folds may appear on the folded portion. Summary of the Invention

[0009] Technical issues

[0010] One aspect of the present invention is to provide a method for manufacturing a secondary battery that increases capacity and prevents or significantly reduces wrinkles when the battery casing is folded, and a bag for the secondary battery.

[0011] Technical solution

[0012] A method for manufacturing a secondary battery according to an embodiment of the present invention includes: a forming step of pressing a pouch sheet using a press die to form a left receiving groove and a right receiving groove that are symmetrical to each other and open upwards, and a bridge connecting the left receiving groove and the right receiving groove to each other, to form a pouch sheet for receiving an electrode assembly; and a folding step of placing the electrode assembly in one of the left receiving groove and the right receiving groove, and folding such that the left receiving groove and the right receiving groove face each other, wherein, in the forming step, the pouch sheet is formed such that the bridge protrudes upwards relative to the bottom surface of the left receiving groove and the right receiving groove, and has an arc-shaped bend formed at the upper end of the bridge.

[0013] According to an embodiment of the present invention, a pouch for a secondary battery includes: a left receiving groove, a right receiving groove, and a bridge, wherein an electrode assembly is received in the left receiving groove and the right receiving groove, and the left receiving groove and the right receiving groove are symmetrical to each other and open upwards, and the bridge is configured to connect the left receiving groove and the right receiving groove to each other, wherein the bridge protrudes upwards relative to the bottom surface of the left receiving groove and the right receiving groove, and has an arc-shaped bend formed at the upper end of the bridge.

[0014] Beneficial effects

[0015] According to the present invention, the battery case can be formed with an optimized structure to accommodate the electrode assembly, and then the battery case can be folded to increase capacity and prevent wrinkles such as bat-ear shapes from appearing when the battery case is folded, or significantly reduce the occurrence of wrinkles. Attached Figure Description

[0016] Figure 1 This is a cross-sectional view showing the formation steps in a method for manufacturing a secondary battery according to an embodiment of the present invention.

[0017] Figure 2 This is a cross-sectional view showing a portion of the pouch including the zigzag surface in a method for manufacturing a secondary battery according to an embodiment of the present invention.

[0018] Figure 3 This is a cross-sectional view showing the main portion of the pouch in a method for manufacturing a secondary battery according to an embodiment of the present invention.

[0019] Figure 4 This is a cross-sectional view showing the portion of the pouch sheet including the bridge in a method for manufacturing a secondary battery according to an embodiment of the present invention.

[0020] Figure 5 This is a cross-sectional view showing the folding step in a method for manufacturing a rechargeable battery according to an embodiment of the present invention.

[0021] Figure 6This is a cross-sectional view illustrating an example of a formation step in a method for manufacturing a secondary battery according to an embodiment of the present invention.

[0022] Figure 7 This is a cross-sectional view illustrating another example of the formation step in a method for manufacturing a secondary battery according to an embodiment of the present invention. Detailed Implementation

[0023] The objects, specific advantages, and novel features of the invention will become more apparent from the following detailed description taken in conjunction with the accompanying drawings. It should be noted that in this specification, reference numerals are added to the parts of the drawings with as many identical numbers as possible, even if they are shown in other drawings. Furthermore, the invention may be embodied in different forms and should not be construed as limited to the embodiments set forth herein. In the following description of the invention, detailed descriptions of related techniques that may unnecessarily obscure the essential points of the invention will be omitted.

[0024] Figure 1 This is a cross-sectional view showing the formation steps in a method for manufacturing a secondary battery according to an embodiment of the present invention.

[0025] refer to Figure 1 According to an embodiment of the present invention, a method for manufacturing a secondary battery includes a forming step of forming a left receiving groove 121 and a right receiving groove 122 and a bridge 123 on a pouch 120, and a folding step of folding the pouch 120 such that the left receiving groove 121 and the right receiving groove 122 face each other.

[0026] In the following text, reference will be made to Figures 1 to 7 A method for manufacturing a secondary battery according to an embodiment of the present invention will be described in more detail.

[0027] refer to Figure 1 In the forming step, the pouch 120 is formed to have a receiving portion for accommodating the electrode assembly 110. Here, in the forming step, the pouch 120 can be pressed using a mold to form a left receiving groove 121 and a right receiving groove 122 that are symmetrical to each other and open upwards, as well as a bridge 123 that connects the left receiving groove 121 and the right receiving groove 122 to each other.

[0028] Furthermore, during the forming step, the bag piece 120 can be formed such that the bottom surfaces 128 and 129 of the left receiving groove 121 and the right receiving groove 122 are symmetrically inclined to each other. Here, during the forming step, the bottom surfaces 128 and 129 of the left receiving groove 121 and the right receiving groove 122 have an inclination that gradually decreases in the direction away from the bridge 123.

[0029] Furthermore, in the forming step, for example, each of the bottom surfaces 128 and 129 of the left receiving groove 121 and the right receiving groove 122 may have an inclination that decreases by an angle of 1° to 5°. That is, in the forming step, for example, each of the bottom surfaces 128 and 129 of the left receiving groove 121 and the right receiving groove 122 may be formed with an inclination angle α that decreases by an angle of 1° to 5°.

[0030] Here, in the forming step, as a specific example, each of the bottom surfaces 128 and 129 of the left receiving groove 121 and the right receiving groove 122 has a slope that decreases at an angle of 1.5° to 3°. Therefore, in the forming step, when each of the bottom surfaces 128 and 129 of the left receiving groove 121 and the right receiving groove 122 is formed to be equal to or less than the upper limit value, cracking due to pressure from the bag 120 can be prevented. When each of the bottom surfaces 128 and 129 of the left receiving groove 121 and the right receiving groove 122 is formed to be equal to or greater than the lower limit value, cracking due to a decrease in the forming depth within the bag 120 can be prevented.

[0031] In the forming step, for example, each of the left receiving groove 121 and the right receiving groove 122 may have a width of 95 mm to 97 mm. Here, as a specific example, each of the left receiving groove 121 and the right receiving groove 122 may have a width of 96.7 mm.

[0032] The electrode assembly 110 can be a rechargeable and dischargeable power generating element, and has a structure in which electrodes 113 and diaphragms 114 are combined and stacked alternately.

[0033] Electrode 113 may include a positive electrode 111 and a negative electrode 112. In addition, diaphragm 114 separates the positive electrode 111 and the negative electrode 112 from each other and electrically insulates them.

[0034] The positive electrode 111 may include a positive current collector (not shown) and a positive active material (not shown) applied to the positive current collector, and the negative electrode 12 may include a negative current collector (not shown) and a negative active material (not shown) applied to the negative current collector.

[0035] For example, the positive current collector can be configured as a foil made of aluminum (Al) material.

[0036] Positive electrode active materials may include, for example, lithium manganese oxide, lithium cobalt oxide, lithium nickel oxide, lithium iron phosphate, or compounds and mixtures thereof containing at least one of these substances.

[0037] For example, the negative current collector can be configured as a foil made of copper (Cu) or nickel (Ni) material.

[0038] Negative electrode active materials may include synthetic graphite, lithium metal, lithium alloys, carbon, petroleum coke, activated carbon, graphite, silicon compounds, tin compounds, titanium compounds, or alloys thereof.

[0039] The separator 114 is made of an insulating material and has a structure that alternates between the positive and negative electrodes. Here, the separator 114 can be disposed between the positive and negative electrodes and on the outer surfaces of the positive and negative electrodes. Here, the separator 114 can be made of, for example, a polyolefin-based resin membrane, such as polyethylene or polypropylene with micropores.

[0040] Figure 2 This is a cross-sectional view showing a portion of the pouch including the zigzag surface in a method for manufacturing a secondary battery according to an embodiment of the present invention.

[0041] refer to Figure 1 and Figure 2 In the forming step, the first curved portion, having outer surfaces of the left receiving groove 121 and the right receiving groove 122 respectively curved downward relative to the outer peripheral surfaces 124 and 125 of the bag piece 120, may have a first curved surface f1, which has an arc shape. Here, the outer peripheral surfaces 124 and 125 of the bag piece 120 may refer to, for example, surfaces provided on the outer edge of the bag piece 120.

[0042] Furthermore, in the forming step, the second curved portion having the shape of the outer surfaces of the left receiving groove 121 and the right receiving groove 122 curving upward relative to the bottom surfaces 128 and 129 of the left receiving groove 121 and the right receiving groove 122 respectively can have a second curved surface f2, which has an arc shape.

[0043] Furthermore, in the forming step, for example, the pouch 120 can be formed such that the width c of each of the bends 126 and 127 formed between the first curved surface f1 and the second curved surface f2 remains equal to or less than 0.5 mm. Here, as a specific example, in the forming step, the pouch 120 can be formed such that the width c of each of the bends 126 and 127 formed between the first curved surface f1 and the second curved surface f2 remains equal to or less than 0.2 mm. Therefore, in the forming step, when the width c of each of the bends 126 and 127 formed between the first curved surface f1 and the second curved surface f2 is formed to be equal to or less than the upper limit value, space efficiency can be optimized. That is, as the width c of each of the bends 126 and 127 formed between the first curved surface f1 and the second curved surface f2 decreases, the volume of the blank space between the rectangular electrode assembly 110 and the pouch 120 can be reduced to improve space efficiency.

[0044] Furthermore, during the forming step, the bag sheet 120 can be formed such that the zigzag surfaces 126 and 127 are planar. Here, the zigzag surface 126 can be the surface between the first inflection point 126a and the second inflection point 126b.

[0045] Here, in the forming step, for example, the pouch 120 can be formed such that each angle r between each outer peripheral surface 124 and 125 of the pouch 120 and each folded surface 126 and 127, and the angle β between each folded surface 126 and 127 and each bottom surface 128 and 129 of the left receiving groove 121 and the right receiving groove 122, are angles of 90° to 100°. Here, in the forming step, as a specific example, the pouch 120 can be formed such that each angle r between each outer peripheral surface 124 and 125 of the pouch 120 and each folded surface 126 and 127, and the angle β between each folded surface 126 and 127 and each bottom surface 128 and 129 of the left receiving groove 121 and the right receiving groove 122, are angles of 93° to 98°.

[0046] Therefore, during the forming step, each angle r between each outer peripheral surface 124 and 125 of the bag piece 120 and each zigzag surface 126 and 127, and each angle β between each zigzag surface 126 and 127 and each bottom surface 128 and 129 of the left receiving groove 121 and the right receiving groove 122, is formed to be equal to or less than the upper limit value, and the width c of each zigzag surface 126 and 127 formed between the first curved surface f1 and the second curved surface f2 can be narrowed. Furthermore, when each angle r between each outer peripheral surface 124 and 125 of the bag piece 120 and each zigzag surface 126 and 127, and each angle β between each zigzag surface 126 and 127 and each bottom surface 128 and 129 of the left receiving groove 121 and the right receiving groove 122, is formed to be equal to or greater than the lower limit value, processability can be improved.

[0047] Figure 3 This is a cross-sectional view showing the main portion of the pouch in a method for manufacturing a secondary battery according to an embodiment of the present invention. Figure 4 This is a cross-sectional view showing the portion of the pouch sheet including the bridge in a method for manufacturing a secondary battery according to an embodiment of the present invention.

[0048] refer to Figure 3 and 4 In the forming step, the bag piece 120 can be formed such that the bridge 123 protrudes upward from the bottom surfaces 128 and 129 of the left receiving groove 121 and the right receiving groove 122, and has an arc-shaped upper curved portion formed at the upper end 123a of the bridge 123.

[0049] Here, in the forming step, the bag 120 can be formed such that the upper end 123a of the bridge 123 has a semi-circle.

[0050] Here, the bridge 123 may have a width W defined by the width of the protrusion that protrudes between the left receiving groove 121 and the right receiving groove 122, and the reference point for the width of the protrusion may be defined by the inflection points b1 and b2 between the bottom surfaces 128 and 129 of the left receiving groove 121 and the right receiving groove 122 and the bend.

[0051] Furthermore, in the forming step, for example, the bag piece 120 can be formed such that the bridge 123 has a width W of 4 mm or less. Additionally, in the forming step, as a specific example, the bag piece 120 can be formed such that the bridge 123 has a width W of 2 mm or less. Therefore, since the width W of the bridge 123 is formed to be equal to or less than the upper limit value, bat-ear shaped folds can be prevented or significantly reduced on the folded portion after the bag piece 120 is folded so that the left receiving groove 121 and the right receiving groove 122 correspond to each other.

[0052] In the forming step, when the length between the lower edge portion p1 of the electrode assembly 110 in the pouch 120 that is adjacent to the bridge 123 and the bridge 123 is d1, the length between the upper edge portion p2 of the electrode assembly 110 in the pouch 120 that is adjacent to the bridge 123 and the bridge 123 is d2, the length of the bridge 123 is d3, and the height of the electrode assembly 110 placed in the pouch 120 is h, the pouch 120 can be formed to satisfy the following condition expression (1).

[0053] The conditional expression for h≤d1+d2+d3 is (1)

[0054] Therefore, since condition expression (1) is satisfied, the side surface of electrode assembly 110 can be completely surrounded when the pouch 120 is folded. Furthermore, if condition expression (1) is not satisfied, then when the pouch 120 is folded so that the left receiving groove 121 and the right receiving groove 122 face each other, the left receiving groove 121 and the right receiving groove 122 may not correspond to each other, but may be misaligned relative to each other.

[0055] In the forming step, when the height of the electrode assembly 110 placed in the pouch 120 is h, and the protrusion height of the bridge 123 relative to the bottom surfaces 128 and 129 of the pouch 120 is a, the pouch 120 can be formed to satisfy the following condition expression (2).

[0056] The conditional expression for h / 2 ≥ a is (2).

[0057] Therefore, since condition expression (2) is satisfied, when the pouch 120 is folded, wrinkles can be prevented in the portion other than the part that completely surrounds the side surface of the electrode assembly. In other words, wrinkles can be prevented or significantly reduced when the length of the portion of the pouch 120 facing the side surface of the electrode assembly 110 is significantly greater than the length of the side surface of the electrode assembly 110, resulting in the pouch not being completely and tightly attached to the side surface of the electrode assembly 110 after folding.

[0058] Figure 5 This is a cross-sectional view showing the folding step in a method for manufacturing a rechargeable battery according to an embodiment of the present invention.

[0059] refer to Figure 5 In the folding step, the electrode assembly 110 can be placed in one of the left receiving groove 121 and the right receiving groove 122, and then the pouch 120 can be folded so that the left receiving groove 121 and the right receiving groove 122 face each other to manufacture the secondary battery 100.

[0060] Here, during the folding step, heat fusion and sealing steps of the outer peripheral surfaces 124 and 125 of the bag sheet 120 can be further performed. Therefore, the receiving space for the electrode assembly 110 can be sealed to close it from the outside.

[0061] Figure 6 This is a cross-sectional view illustrating an example of a formation step in a method for manufacturing a secondary battery according to an embodiment of the present invention. Figure 7 This is a cross-sectional view illustrating another example of the formation step in a method for manufacturing a secondary battery according to an embodiment of the present invention.

[0062] refer to Figure 6 In the forming step, for example, the bag piece 120 can be formed such that the width c1 of the zigzag surface 126' formed between the first curved surface f1' and the second curved surface f2' is 0.35 mm. Here, in the forming step, the bag piece 120 can be formed such that each angle r1 between each outer peripheral surface 124 and 125 of the bag piece 120 and the zigzag surface 126', and the angle β1 between the zigzag surface 126' and each bottom surface 128 and 129 of the left receiving groove 121 and the right receiving groove 122, are 95°. Here, the first curved surface f1' can be formed as a portion of a circle with radius R1, and the second curved surface f2' can be formed as a portion of a circle with radius R2. Here, radius R1 is 1.5 mm, and radius R2 is 2 mm.

[0063] refer to Figure 7In the forming step, as another example, the pouch 120 can be formed such that the width c2 of the zigzag surface 126" formed between the first curved surface f1" and the second curved surface f2" is 0.25 mm. Here, in the forming step, the pouch 120 can be formed such that each angle r2 between each outer peripheral surface 124 and 125 of the pouch 120 and the zigzag surface 126" and the angle β2 between the zigzag surface 126" and each bottom surface 128 and 129 of the left receiving groove 121 and the right receiving groove 122 is formed to be 96.1°. Here, the first curved surface f1" can be formed as a portion of a circle with radius R1, and the second curved surface f2" can be formed as a portion of a circle with radius R2. Here, radius R1 is 1.5 mm, and radius R2 is 2 mm.

[0064] <Example 1>

[0065] When the left receiving groove 121 and the right receiving groove 122, which are symmetrical to each other, are formed in the bag sheet, the bag sheet is formed such that the bottom surfaces 128 and 129 of each of the left receiving groove 121 and the right receiving groove 122 are inclined. Furthermore, the bridge has a width W of 4.0 mm, and the width c of the tortuous surface formed between the first curved surface f1 and the second curved surface f2 is 0.5 mm. Then, the secondary battery is manufactured (see...). Figures 1 to 3 ).

[0066] <Example 2>

[0067] refer to Figure 1 and 2 When the left receiving groove 121 and the right receiving groove 122, which are symmetrical to each other, are formed in the bag sheet, the bag sheet is formed such that the bottom surfaces 128 and 129 of each of the left receiving groove 121 and the right receiving groove 122 are inclined. Furthermore, the bridge has a width W of 2.0 mm, and the width c of the tortuous surface formed between the first curved surface f1 and the second curved surface f2 is 0.35 mm. Then, the secondary battery is manufactured (see...). Figures 1 to 3 ).

[0068] <Comparative Example 1>

[0069] When the left receiving groove 121 and the right receiving groove 122, which are symmetrical to each other, are formed in the bag sheet, the bag sheet is formed such that the bottom surface of each of the left receiving groove 121 and the right receiving groove 122 is not inclined but horizontal and flat. In addition, the bridge has a width W of 5.0 mm, and the width c of the tortuous surface formed between the first curved surface f1 and the second curved surface f2 is 1.0 mm. Then, the secondary battery is manufactured.

[0070] Table 1

[0071]

[0072] As shown in Table 1, in Comparative Example 1, the bat-ear-shaped pleats have a size of 4.5 mm or larger. On the other hand, in Example 1, the bat-ear-shaped pleats have a size of 3.4 mm, and in Example 2, the bat-ear-shaped pleats have a size of 2 mm or smaller. Therefore, it can be seen that when the bag is folded, the pleats at the folded portion in Example 1 are smaller than those in Comparative Example 1, and it can also be seen that the pleats in Example 2 are smaller than those in Comparative Example 1. As a result, in the secondary battery manufactured according to the method of manufacturing a secondary battery according to an embodiment of the present invention, as shown in Examples 1 and 2, compared with Comparative Example 1 of the manufacturing method according to the related art, the pleats at the folded portion are significantly reduced, thereby significantly reducing damage to the appearance and the occurrence of cracks. Hereinafter, a bag for a secondary battery according to an embodiment of the present invention will be described.

[0073] refer to Figure 1 According to an embodiment of the present invention, a pouch 120 for a secondary battery includes a left receiving groove 121 and a right receiving groove 122, and a bridge 123 connecting the left receiving groove 121 and the right receiving groove 122 to each other. The left receiving groove 121 and the right receiving groove 122 receive electrode assemblies, are symmetrical to each other, and open upwards.

[0074] The pouch for a secondary battery according to an embodiment of the present invention relates to a pouch 120 for a secondary battery disposed in a secondary battery 100 manufactured by a method for manufacturing a secondary battery according to the foregoing embodiment of the present invention; therefore, repeated content will be briefly described.

[0075] refer to Figure 2 The first curved portion, which has the outer surfaces of the left receiving groove 121 and the right receiving groove 122 respectively curved downward relative to the outer peripheral surfaces 124 and 125 of the bag piece 120, may have a first curved surface f1, which has an arc shape.

[0076] Furthermore, the second curved portion, having outer surfaces of the left receiving groove 121 and the right receiving groove 122 that curve upward relative to the bottom surfaces 128 and 129 of the left receiving groove 121 and the right receiving groove 122 respectively, can have a second curved surface f2, which has an arc shape. Additionally, the bag piece 120 can be formed such that the width c of each of the folded surfaces 126 and 127 formed between the first curved surface f1 and the second curved surface f2 remains equal to or less than 0.5 mm.

[0077] The pouch 120 can be formed such that each folded surface 126 and 127 has a planar shape, and each angle r between each outer peripheral surface 124 and 125 of the pouch 120 and each folded surface 126 and 127, and each angle β between each folded surface 126 and 127 and each bottom surface 128 and 129 of the left receiving groove 121 and the right receiving groove 122, is formed to be an angle of 93° to 98°.

[0078] refer to Figure 3 The bridge 123 can protrude upward from the bottom surfaces 128 and 129 of the left receiving groove 121 and the right receiving groove 122, and has an arc-shaped bend that can be formed at the upper end 123a of the bridge 123.

[0079] Furthermore, the bag 120 can be formed such that the bridge 123 has a width W of 1 mm to 2 mm.

[0080] While the invention has been specifically shown and described with reference to exemplary embodiments thereof, the method for manufacturing a secondary battery and the bag for the secondary battery according to the invention are not limited thereto. Those skilled in the art will understand that various changes in form and detail may be made without departing from the spirit and scope of the invention.

[0081] Furthermore, the scope of protection of this invention will be defined by the appended claims.

Claims

1. A method for manufacturing a secondary battery, the method comprising: The forming step involves pressing the bag sheet using a molding process to create left and right accommodating grooves that are symmetrical to each other and open upwards, as well as a bridge connecting the left and right accommodating grooves to each other. and In the folding step, the electrode assembly is placed in one of the left and right receiving grooves, and the bag is folded so that the left and right receiving grooves face each other. In the forming step, the bag piece is formed such that the bridge protrudes upward relative to the bottom surfaces of the left and right receiving grooves, and an arc-shaped upper curved portion is formed at the upper end of the bridge. In the forming step, when the length between the lower edge of the electrode assembly in the bag that contacts the bridge and the bridge is d1, the length between the upper edge of the electrode assembly in the bag that contacts the bridge and the bridge is d2, the length of the bridge is d3, the height of the electrode assembly placed on the bag is h, and the protrusion height of the bridge relative to the bottom surface of the bag is a, the bag is formed to satisfy the following conditions: h ≤ d1 + d2 + d3 and h / 2 ≥ a, and the bag is formed such that the bottom surfaces of the left receiving groove and the right receiving groove are symmetrically inclined to each other. The bottom surfaces of the left and right receiving grooves have a gradually decreasing inclination in the direction away from the bridge, such that the first end of the bottom surface of the electrode assembly near the bridge contacts the bottom surface of the left receiving groove, and the second end of the bottom surface of the electrode assembly away from the bridge does not contact the bottom surface of the left receiving groove.

2. The method according to claim 1, wherein, In the forming step, each bottom surface of the left and right receiving grooves has a slope that decreases at an angle of 1° to 5°.

3. The method according to claim 1, wherein, In the forming step, each bottom surface of the left and right receiving grooves has a slope that decreases at an angle of 1.5° to 3°.

4. The method according to claim 1, wherein, In the forming step, an outer peripheral surface is formed in the bag sheet that is connected to the outer surfaces of the left and right receiving grooves.

5. The method according to claim 4, wherein, In the folding step, heat fusion and sealing steps are performed on the outer peripheral surface of the bag sheet.

6. The method according to claim 4, wherein, In the forming step, the first curved portion having the outer surfaces of the left and right receiving grooves respectively curved downward relative to the outer peripheral surface of the bag sheet has a first curved surface, the first curved surface having an arc shape. The second curved portion, having the outer surfaces of the left and right receiving grooves respectively curved upward relative to the bottom surfaces of the left and right receiving grooves, has a second curved surface, which has an arc shape.

7. The method according to claim 6, wherein, In the forming step, the bag is formed such that the width of each fold formed between the first curved surface and the second curved surface is 0.5 mm or less.

8. The method according to claim 6, wherein, In the forming step, the bag is formed such that the width of each fold formed between the first curved surface and the second curved surface is 0.2 mm or less.

9. The method according to claim 6, wherein, In the forming step, the bag is formed such that each folded surface formed between the first curved surface and the second curved surface has a planar shape.

10. The method according to claim 9, wherein, In the forming step, the angle between each outer peripheral surface of the bag sheet and each folded surface, as well as the angle between each folded surface and each bottom surface of the left and right receiving grooves, are formed to be between 90° and 100°.

11. The method according to claim 9, wherein, In the forming step, the angle between each outer peripheral surface of the bag sheet and each folded surface, as well as the angle between each folded surface and each bottom surface of the left and right receiving grooves, are formed to be between 93° and 98°.

12. The method according to claim 1, wherein, In the forming step, the bag is formed such that the upper end of the bridge has a semi-circle.

13. The method according to claim 1, wherein, In the forming step, a downwardly curved portion with an arc shape is formed at the lower end of the bridge and connected to the bottom surface of each of the left and right receiving grooves.

14. The method according to claim 1, wherein, In the forming step, the bag is formed such that the bridge has a width (W) of 4 mm or less.

15. The method according to claim 1, wherein, In the forming step, the bag is formed such that the bridge has a width (W) of 1 mm to 2 mm.

16. A bag for a secondary battery, the bag comprising: The bag flap, in its folded form, comprises: A left receiving groove and a right receiving groove, in which the electrode assembly is housed, and the left and right receiving grooves are symmetrical to each other and open upwards; and The bridge is configured to connect the left receiving recess and the right receiving recess to each other. The bridge protrudes upward relative to the bottom surfaces of the left and right receiving grooves, and has an arc-shaped upper bend formed at the upper end of the bridge. The bag is formed such that the bottom surfaces of the left receiving groove and the right receiving groove are symmetrically inclined to each other. The bottom surfaces of the left and right receiving grooves have a gradually decreasing slope in the direction away from the bridge, such that a first end of the bottom surface of the electrode assembly near the bridge contacts the bottom surface of the left receiving groove, and a second end of the bottom surface of the electrode assembly away from the bridge does not contact the bottom surface of the left receiving groove. The bridge has a width (W) of 4 mm or less.

17. The bag of claim 16, wherein each bottom surface of the left receiving groove and the right receiving groove has a slope that decreases at an angle of 1° to 5°.

18. The bag of claim 16, wherein the bottom surface of each of the left and right receiving recesses has a slope that decreases at an angle of 1.5° to 3°.

19. The bag of claim 16, wherein the bag further comprises: The outer peripheral surface connected to the outer surfaces of the left and right receiving grooves.

20. The bag according to claim 19, wherein the first curved portion having the outer surfaces of the left and right receiving grooves respectively curved downward relative to the outer peripheral surface of the bag sheet has a first curved surface, the first curved surface having an arc shape. The second curved portion, having the outer surfaces of the left and right receiving grooves respectively curved upward relative to the bottom surfaces of the left and right receiving grooves, has a second curved surface, which has an arc shape.

21. The bag of claim 20, wherein the bag sheet is formed such that the width of each fold formed between the first curved surface and the second curved surface is 0.5 mm or less.

22. The bag of claim 20, wherein the bag sheet is formed such that the width of each fold formed between the first curved surface and the second curved surface is 0.2 mm or less.

23. The bag of claim 20, wherein the bag sheet is formed such that each folded surface formed between the first curved surface and the second curved surface has a planar shape.

24. The bag of claim 23, wherein the angle between each outer peripheral surface of the bag sheet and each folded surface, and the angle between each folded surface and each bottom surface of the left receiving groove and the right receiving groove, are formed to be 90° to 100°.

25. The bag of claim 23, wherein the angle between each outer peripheral surface of the bag sheet and each folded surface, and the angle between each folded surface and each bottom surface of the left receiving groove and the right receiving groove, are formed to be 93° to 98°.

26. The bag of claim 16, wherein a downwardly curved portion having an arcuate shape is formed at the lower end of the bridge and connected to the bottom surface of each of the left and right receiving grooves.

27. The bag according to claim 16, wherein, In the bag sheet, the width (W) of the bridge is 1 mm to 2 mm.

28. A bag for a secondary battery, the bag comprising: The bag flap, in its folded form, comprises: A left receiving groove and a right receiving groove, in which the electrode assembly is housed, and the left and right receiving grooves are symmetrical to each other and open upwards; and The bridge is configured to connect the left receiving recess and the right receiving recess to each other. The bridge protrudes upward relative to the bottom surfaces of the left and right receiving grooves, and has an arc-shaped upper bend formed at the upper end of the bridge. Wherein, when the length between the lower edge of the electrode assembly in the bag that contacts the bridge and the bridge is d1, the length between the upper edge of the electrode assembly in the bag that contacts the bridge and the bridge is d2, the length of the bridge is d3, the height of the electrode assembly placed on the bag is h, and the protrusion height of the bridge relative to the bottom surface of the bag is a, the bag is formed to satisfy the following conditions: h≤d1+d2+d3 and h / 2≥a. The bag is formed such that the bottom surfaces of the left receiving groove and the right receiving groove are symmetrically inclined to each other. The bottom surfaces of the left and right receiving grooves have a gradually decreasing inclination in the direction away from the bridge, such that the first end of the bottom surface of the electrode assembly near the bridge contacts the bottom surface of the left receiving groove, and the second end of the bottom surface of the electrode assembly away from the bridge does not contact the bottom surface of the left receiving groove.

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