Electrode assembly, manufacturing method for electrode assembly, secondary battery and manufacturing method for secondary battery

Abstract

The present invention relates to an electrode assembly, a method for manufacturing an electrode assembly, a secondary battery, and a method for manufacturing a secondary battery.

Description

Technology Field

[0001] This application claims the benefit of the filing date of Korean Patent Application No. 10-2022-0035393 filed with the Korean Intellectual Property Office on March 22, 2022, and all contents disclosed in the document of said Korean patent application are incorporated into this specification.

[0002] The present invention relates to an electrode assembly, a method for manufacturing an electrode assembly, a secondary battery, and a method for manufacturing a secondary battery. Background Technology

[0003] Recently, as the demand for portable electronic products such as laptops, video cameras, and mobile phones has increased rapidly, and the development of electric vehicles, energy storage batteries, robots, and satellites has accelerated, much research is being conducted on secondary batteries used as their power sources.

[0004] Examples of such rechargeable batteries include nickel-cadmium batteries, nickel-hydrogen batteries, nickel-zinc batteries, and lithium-ion batteries. Among these, lithium-ion batteries are gaining popularity as power sources for mobile devices due to their excellent characteristics, such as lightweight design, long lifespan, and high capacity.

[0005] Generally, a lithium secondary battery is constructed by housing an electrode assembly, composed of a positive electrode, a negative electrode, and a separator interposed between the positive and negative electrodes, in a stacked or wound structure within a case made of a metal can or laminate sheet, and by injecting or impregnating an electrolyte into the interior.

[0006] The electrode assembly, consisting of a positive electrode, separator, and negative electrode structure that constitutes a secondary battery, is broadly classified into jellyroll type (wound type) and stack type (laminated type) based on its structure. The jellyroll type is a structure in which a separator is interposed between long sheet-shaped positive and negative electrodes coated with active material and wound, while the stack type is a structure in which multiple positive and negative electrodes of a predetermined size are sequentially stacked with a separator interposed between them. To prevent current flow between the positive and negative electrodes in a secondary battery, the separator is generally made larger than the two electrodes. For example, in the case of a jellyroll type electrode assembly, the separator is partially exposed along the winding axis of the electrode assembly. Prior art literature

[0007] Korean Published Patent Application No. 10-2005-0080516 The problem to be solved

[0008] Generally, for secondary batteries, an electrode assembly is inserted into a battery casing with an opening on one side, and an electrolyte is injected. Subsequently, a battery cap is placed over the opening of the casing, and the joint between the casing and the cap is sealed. At this stage, a process such as laser welding is performed to prevent leakage of the electrolyte.

[0009] Heat is generated during this welding process, and this heat damages the electrode assembly near the weld, particularly the separator that is exposed relative to the two electrodes. If the separator is damaged, current may flow between the anode and cathode, so research is needed to prevent damage caused by heat during this welding process.

[0010] The present specification provides an electrode assembly capable of preventing damage to the separator of a jellyroll-type electrode assembly, a method for manufacturing the electrode assembly, a secondary battery including the electrode assembly, and a method for manufacturing the secondary battery. means of solving the problem

[0011] One embodiment of the present invention provides a method for manufacturing an electrode assembly comprising: a step of preparing an electrode assembly having a structure in which a first electrode, a second electrode, and a separator provided between the first electrode and the second electrode are wound; and a step of forming a portion of the uppermost part of the electrode assembly in a shape bent in the direction of the winding center, wherein the forming step is formed such that the difference between the longest diameter and the shortest diameter of the formed portion of the electrode assembly is 0.1 mm or more and 20 mm or less.

[0012] One embodiment of the present invention provides a method for manufacturing a secondary battery comprising the steps of: inserting an electrode assembly manufactured according to the above manufacturing method into a battery casing; injecting an electrolyte into the battery casing; placing a battery casing cap in an opening of the battery casing; and welding and sealing the battery casing cap.

[0013] One embodiment of the present invention provides an electrode assembly having a structure in which a first electrode, a second electrode, and a separator provided between the first electrode and the second electrode are wound, wherein a portion of the upper outermost part of the electrode assembly is bent in the direction of the winding center, and the difference between the longest diameter and the shortest diameter of the bent portion of the electrode assembly is 0.1 mm or more and 20 mm or less.

[0014] One embodiment of the present invention provides a secondary battery comprising the electrode assembly. Effects of the invention

[0015] In the present invention, by molding the upper part of the electrode assembly, when the electrode assembly is inserted into a secondary battery, a separation distance can be secured between the laser welded portion of the sealing step and the separator of the electrode assembly. Therefore, damage to the separator caused by heat generated during laser welding in the sealing step can be prevented. Consequently, since the separator of a secondary battery including the electrode assembly of the present invention is not damaged, the safety of the secondary battery can be ensured. Brief explanation of the drawing

[0016] Figure 1 schematically shows the shape of an electrode assembly (1) having a general wound structure. FIG. 2 is a perspective view showing a molded portion (12) of an electrode assembly (1) according to one embodiment of the present invention. FIG. 3 is a reference diagram for showing the shape of a molded portion of an electrode assembly (1) according to one embodiment of the present invention in terms of angle. FIG. 4 shows a molded example of an electrode assembly (1) according to one embodiment of the present invention. FIG. 5 schematically illustrates the molding step in a method for manufacturing an electrode assembly (1) according to one embodiment of the present invention. FIG. 6 is an enlarged view of an electrode assembly (1) manufactured according to one embodiment of the present invention when inserted into a battery outer casing. Figure 7 is a cross-section of a secondary battery according to Comparative Example 1. Figure 8 shows the upper part of the electrode assembly after removing the battery outer cap of the secondary battery according to Comparative Example 1. Figure 9 is an enlarged view of the separator of the electrode assembly inside the secondary battery according to Comparative Example 1. FIG. 10 (a) is a top view of an electrode assembly formed according to Example 1, and (b) is a side view of the formed electrode assembly. Figure 11 is a photograph showing the separator after disassembling the secondary battery according to Example 1. FIG. 12 is a schematic diagram showing an electrode assembly manufactured according to one embodiment, observed from above. Specific details for implementing the invention

[0017] The present specification will be described in more detail below.

[0018] The present invention is described in detail below so that those skilled in the art can easily implement it. However, the present invention may be embodied in various different forms and is not limited to the configurations described herein.

[0019] In this specification, when a part is described as "comprising" a certain component, this means that, unless specifically stated otherwise, it does not exclude other components but may include additional components.

[0020] In this specification, 'p to q' means a range of 'p or more and q or less'.

[0021] In this specification, the present invention is described in detail with reference to the drawings. However, the drawings are intended to illustrate the present invention, and the scope of the present invention is not limited by the drawings.

[0022] One embodiment of the present invention provides a method for manufacturing an electrode assembly comprising: a step of preparing an electrode assembly having a structure in which a first electrode, a second electrode, and a separator provided between the first electrode and the second electrode are wound; and a step of forming a portion of the uppermost part of the electrode assembly in a shape bent in the direction of the winding center, wherein the forming step is formed such that the difference between the longest diameter and the shortest diameter of the formed portion of the electrode assembly is 0.1 mm or more and 20 mm or less.

[0023] Forming a portion from the outermost angle toward the winding center direction means forming a portion from the outermost angle toward the winding center direction, including the outermost angle.

[0024] The term "upper part" of the above electrode assembly refers to the direction in which the battery outer cap is placed or sealed in the step of placing the battery outer cap in the opening of the battery outer material and welding to seal it in the secondary battery manufacturing method described below.

[0025] By forming a portion of the upper outermost part of the electrode assembly in the direction of the winding center into a bent shape in the direction of the winding center, a separation distance can be secured between the laser welded portion of the sealing step and the separator of the electrode assembly when the electrode assembly is inserted into a secondary battery. Therefore, damage to the separator caused by heat generated during laser welding in the sealing step can be prevented.

[0026] A further embodiment of the present invention provides a method for manufacturing an electrode assembly, wherein the forming step forms the difference between the longest diameter and the shortest diameter of the formed portion of the electrode assembly to be 0.1 mm or more and 20 mm or less.

[0027] In another embodiment, the forming step may be formed such that the difference between the longest diameter and the shortest diameter of the formed portion of the electrode assembly is 0.1 mm or more, 0.2 mm or more, 2 mm or more, 4 mm or more, or 6 mm or more. The forming step may be formed such that the difference between the longest diameter and the shortest diameter of the formed portion of the electrode assembly is 20 mm or less, 18 mm or less, 16 mm or less, 14 mm or less, 12 mm or less, 10 mm or less, 9 mm or less, or 8 mm or less.

[0028] Accordingly, the above method for manufacturing the electrode assembly can be applied to a microelectrode assembly used in a micro battery.

[0029] A portion from the outermost edge toward the center of the winding may be two or more sheets including the outermost sheet of the electrode assembly.

[0030] That is, the outermost sheet of the electrode assembly must be included in the molding, and two or more sheets can be formed in a folded shape in the direction of the winding center.

[0031] The upper portion of the electrode assembly may include a range of at least 10 μm in a direction parallel to the winding center axis from the top of the electrode assembly.

[0032] That is, it may include a range up to 20 μm, a range up to 30 μm, a range up to 100 μm, a range up to 500 μm, a range up to 1 mm, and a range up to 10 mm.

[0033] When the electrode assembly manufactured according to the above manufacturing method is observed from above, the shape of the deformed upper region can be observed as a circle.

[0034] In addition, as shown in FIG. 12, the overall shape is close to a circle, but it can be observed as a deformed circle in which some of the lines forming the circle are composed of curves that are partially deformed like waves. That is, a part of the circle may be in a distorted shape. FIG. 10(a) shows an electrode assembly manufactured according to one embodiment as observed from above.

[0035] By forming a portion of the upper outermost part of the electrode assembly in the direction of the winding center into a bent shape in the direction of the winding center, a separation distance can be secured between the laser welded portion of the sealing step and the separator of the electrode assembly when the electrode assembly is inserted into a secondary battery. Therefore, damage to the separator caused by heat generated during laser welding in the sealing step can be prevented.

[0036] FIG. 5 schematically illustrates a molding step in a method for manufacturing an electrode assembly (1) according to one embodiment of the present invention. As shown in FIG. 5, in the molding process, pressure may be applied to the electrode assembly (1) to form it, and the pressure is applied in a direction parallel to the winding center axis. In this case, a constant pressure may be applied to the upper part of the electrode assembly (1) of the present invention using a servo motor (3).

[0037] In the above-mentioned molding process, the pressure and pressurization time applied to the electrode assembly may be varied depending on the diameter and height of the electrode assembly, the range to be molded, the materials of the electrode and separator, the number of turns of the electrode assembly, etc. That is, the pressure and pressurization time are not limited as long as they allow for molding into a shape in which a separation distance is secured between the welded portion of the battery outer material and the battery outer cap described later and the electrode assembly.

[0038] The pressure applied to the electrode assembly is, for example, 0.1 kgf / cm² 2 Above 20 kgf / cm² 2 It may be less than or equal to 0.5 kgf / cm² 2 Above 20 kgf / cm² 2 It may be less than or equal to 1 kgf / cm² 2 Above 20 kgf / cm² 2 It may be less than, but is not limited thereto as described above.

[0039] The above pressurization time may be, for example, 0.1 seconds or more and 1 minute or less, 0.5 seconds or more and 50 seconds or less, 1 second or more and 30 seconds or less, and 3 seconds or more and 10 seconds or less, but is not limited thereto as described above.

[0040] In the step of preparing the above electrode assembly, an electrode assembly having a wound structure can be prepared by interposing a separator between the first electrode and the second electrode and winding in one direction, and having a first electrode having a sheet shape and a second electrode.

[0041] FIG. 1 schematically shows the shape of an electrode assembly (1) having a general wound structure, and the winding center axis (10) can be identified.

[0042] The first electrode may be an anode, and the second electrode may be a cathode.

[0043] The first electrode may be a negative electrode, and the second electrode may be a positive electrode.

[0044] The above positive electrode may include a positive current collector layer and a positive active material layer, and the positive active material layer may include a positive active material.

[0045] The material of the positive current collector layer is not particularly limited as long as it is conductive without causing chemical changes in the battery, and for example, copper, stainless steel, aluminum, nickel, titanium, calcined carbon, or a surface treated with carbon, nickel, titanium, silver, etc. on the surface of copper, aluminum, or stainless steel may be used. Fine irregularities may be formed on the surface of the current collector to increase the adhesion of the positive active material. For example, it may be used in various forms such as a film, sheet, foil, net, porous body, foam, nonwoven fabric, etc.

[0046] The above-mentioned positive electrode active material may be a commonly used positive electrode active material. The above-mentioned positive electrode active material is a compound capable of reversible intercalation and deintercalation of lithium, and specifically, may include a lithium transition metal composite oxide comprising lithium and at least one transition metal composed of nickel, cobalt, manganese, and aluminum. More specifically, the lithium transition metal composite oxide may include lithium and a transition metal comprising nickel, cobalt, and manganese.

[0047] The above cathode may include a cathode current collector layer and a cathode active material layer, and the cathode active material layer may include a cathode active material.

[0048] The material of the above-mentioned negative electrode current collector layer is not particularly limited as long as it has high conductivity without causing chemical changes in the battery, and for example, copper, stainless steel, aluminum, nickel, titanium, calcined carbon, copper or stainless steel surface treated with carbon, nickel, titanium, silver, etc., and aluminum-cadmium alloy may be used. In addition, fine irregularities may be formed on the surface to strengthen the bonding strength of the negative electrode active material, and it may be used in various forms such as films, sheets, foils, nets, porous bodies, foams, and nonwoven fabrics.

[0049] The above-mentioned negative electrode active material may be a commonly used negative electrode active material, and a compound capable of reversible intercalation and deintercalation may be used. Specifically, the above-mentioned negative electrode active material may be a single material selected from the group consisting of carbon-based active materials, silicon-based active materials, metal-based active materials capable of alloying with lithium, and lithium-containing nitrides, or a mixture of two or more of these.

[0050] The above separator separates the negative electrode and the positive electrode and provides a pathway for the movement of lithium ions. It can be used without special limitations as long as it is typically used as a separator in a secondary battery, and it is particularly desirable that it has low resistance to the movement of electrolyte ions and excellent electrolyte wettability. Specifically, a porous polymer film, such as a porous polymer film made of a polyolefin-based polymer like ethylene homopolymer, propylene homopolymer, ethylene / butene copolymer, ethylene / hexene copolymer, and ethylene / methacrylate copolymer, or a laminated structure of two or more layers thereof may be used. In addition, a conventional porous nonwoven fabric, such as a nonwoven fabric made of high-melting-point glass fiber or polyethylene terephthalate fiber, may be used. Furthermore, a coated separator containing ceramic components or polymer materials may be used to ensure heat resistance or mechanical strength, and it may optionally be used in a single-layer or multi-layer structure.

[0051] One embodiment of the present invention provides a method for manufacturing an electrode assembly in which the molding step is performed at 40°C to 120°C.

[0052] The above-mentioned molding step may be performed at 40°C or higher, 50°C or higher, 60°C or higher, or 70°C or higher. The above-mentioned molding step may be performed at 120°C or lower, 110°C or lower, 100°C or lower, or 90°C or lower.

[0053] When molding at the above temperature, the shape of the upper part of the electrode assembly can be bent while effectively maintaining the function of the separator of the electrode assembly.

[0054] When the molding step is at 40°C or higher, the molding maintenance effect of the electrode assembly is excellent, and when the molding step is at 120°C or lower, the pores of the separator, such as the ion movement channels of the separator, are not blocked, so the resistance characteristics may be excellent.

[0055] In addition, if the temperature of the molding step exceeds 120°C, the function of the separator of the electrode assembly may be degraded depending on the material of the separator. For example, in the case of a polyolefin-based separator, it melts at 130°C or higher, causing the pores of the separator to become clogged and the ion conductivity to decrease, which may lead to a degradation of the separator's function.

[0056] One embodiment of the present invention provides a method for manufacturing an electrode assembly in which the molding step is such that the diameter of the molded portion of the electrode assembly becomes smaller toward the top.

[0057] FIG. 2 is a perspective view of an electrode assembly (1) with its upper portion molded according to one embodiment of the present invention. The molded portion (12) and the uppermost portion (11) are shown.

[0058] The above-mentioned molded portion (12) is a portion of the electrode assembly modified according to the molding of the present invention. The uppermost portion (11) is the outermost surface among the molded portions of the electrode assembly. The diameter (L) of the molded portion (12) of the electrode assembly is the diameter of the surface perpendicular to the winding center axis (10).

[0059] At this time, the diameter (L) of the molded part can be molded to become smaller as it goes toward the top (11).

[0060] In addition, the diameter (L) of the molded part can be molded to become continuously smaller as it approaches the top (11). FIG. 2 is a schematic perspective view showing an example in which the diameter (L) of the molded part becomes continuously smaller as it approaches the top (11).

[0061] In addition, the diameter (L) of the molded part can be molded to become intermittently smaller as it approaches the top (11). FIG. 4 is a schematic perspective view showing an example in which the diameter (L) of the molded part becomes intermittently smaller as it approaches the top (11).

[0062] In addition, the diameter (L) of the molded part may be molded to decrease continuously and intermittently as it approaches the top (11).

[0063] One embodiment of the present invention provides a method for manufacturing an electrode assembly in which the forming step forms an angle between the formed portion of the electrode assembly and the winding center axis of 10° or more and 80° or less.

[0064] In another embodiment, the angle formed between the molded portion of the electrode assembly and the winding center axis may be 20° or more and 80° or less, 30° or more and 80° or less, 40° or more and 80° or less, and 50° or more and 70° or less.

[0065] In another embodiment, the angle formed between the molded portion of the electrode assembly and the winding center axis may be 10° or more, 20° or more, 30° or more, 40° or more, 50° or more, or 60° or more. The angle formed between the molded portion of the electrode assembly and the winding center axis may be 80° or less, 75° or less, 70° or less, or 65° or less.

[0066] FIG. 3 is a reference diagram for showing the shape of a molded part (12) in angles according to one embodiment of the present invention.

[0067] The angle (θ) formed by the molded portion (12) of the electrode assembly and the winding center axis (10) means the acute angle formed at the point where the line (120) extending the molded portion (12) and the line (100) extending the winding center axis (10) meet.

[0068] One embodiment of the present invention provides a method for manufacturing an electrode assembly in which the molding step involves molding the shortest diameter of the molded portion of the electrode assembly to be 50% or more and 99% or less of the longest diameter.

[0069] In another embodiment, the forming step may be formed such that the shortest diameter of the formed portion of the electrode assembly is 50% or more, 60% or more, 70% or more, or 80% or more of the longest diameter. The forming step may be formed such that the shortest diameter of the formed portion of the electrode assembly is 99% or less, 97% or less, 95% or less, 93% or less, or 91% or less of the longest diameter.

[0070] In the electrode assembly (1) of FIG. 2, the longest diameter (L1) and the shortest diameter (L2) of the molded portion (12) are shown.

[0071] One embodiment of the present invention provides a method for manufacturing a secondary battery, comprising the steps of: inserting an electrode assembly manufactured according to the above manufacturing method into a battery casing; injecting an electrolyte into the battery casing; placing a battery casing cap in an opening of the battery casing; and welding and sealing the battery casing cap.

[0072] In the step of inserting the electrode assembly manufactured according to the above manufacturing method into the battery casing, the battery casing may be a cylindrical can and has a shape with one side open. The electrode assembly can be inserted into the interior through the opening.

[0073] In the step of injecting an electrolyte into the battery casing, the electrolyte can be injected through an opening in the battery casing while the electrode assembly is inserted into the battery casing. In addition to the electrolyte components, the electrolyte may further include one or more additives for the purpose of improving the battery life characteristics, suppressing battery capacity reduction, and improving the battery discharge capacity.

[0074] The above electrolyte may include organic liquid electrolytes, inorganic liquid electrolytes, solid polymer electrolytes, gel-type polymer electrolytes, solid inorganic electrolytes, molten inorganic electrolytes, etc., which can be used in the manufacture of lithium secondary batteries, but is not limited to these.

[0075] In the step of placing a battery outer cap in the opening of the battery outer material, the battery outer cap is placed to completely cover the opening of the battery outer material. The battery outer cap may be circular, and the shape of the battery outer cap may match the shape of the opening of the battery outer material.

[0076] One embodiment of the present invention provides a method for manufacturing a secondary battery in which the difference between the distance (b1) from the battery outer cap to the outermost unfolded sheet of the electrode assembly and the distance (b2) from the battery outer cap to the top of the battery assembly is 10 μm to 10 mm, and the difference between the distance (a1) from the side of the battery outer material to the top of the battery assembly and the distance (a2) from the side of the battery outer material to the outermost unfolded sheet of the electrode assembly is 0.05 mm to 5 mm.

[0077] In another embodiment, the difference between the distance (b1) from the battery outer cap to the outermost unfolded sheet of the electrode assembly and the distance (b2) from the battery outer cap to the top of the battery assembly may be 10 μm or more, 30 μm or more, 50 μm or more, 70 μm or more, 90 μm or more, 0.1 mm or more, 0.2 mm or more, or 0.3 mm or more. The difference between the distance (b1) from the battery outer cap to the outermost unfolded sheet of the electrode assembly and the distance (b2) from the battery outer cap to the top of the battery assembly may be 10 mm or less, 8 mm or less, 6 mm or less, 4 mm or less, 2 mm or less, 1 mm or less, 0.8 mm or less, or 0.6 mm or less.

[0078] In another embodiment, the difference between the distance (a1) from the side of the battery casing to the top of the battery assembly and the distance (a2) from the side of the battery casing to the unfolded outermost sheet of the electrode assembly may be 0.05 mm or more, 0.1 mm or more, 0.3 mm or more, 0.5 mm or more, 0.7 mm or more, 0.9 mm or more, or 1 mm or more. The difference between the distance (a1) from the side of the battery casing to the top of the battery assembly and the distance (a2) from the side of the battery casing to the unfolded outermost sheet of the electrode assembly may be 5 mm or less, 4 mm or less, 3 mm or less, 2 mm or less, or 1.5 mm or less.

[0079] FIG. 6 is an enlarged view of a secondary battery in which an electrode assembly (1) manufactured according to one embodiment of the present invention is inserted into a battery outer casing (5), and an insulator (4) and a battery outer cap (2) are arranged. The upper part of the electrode assembly is bent so that a separation distance from the battery outer cap (2) is formed as described above.

[0080] In the step of welding and sealing the battery outer cap, a step of sealing the joint between the battery outer material and the battery outer cap is required to prevent the electrolyte inside the injected battery outer material from leaking out. A laser welding process may be used for the sealing.

[0081] The laser welding described above may weld the edge of the battery outer cap along the path of the joint between the battery outer material and the battery outer cap. During this welding process, heat is generated, and this heat damages the electrode assembly adjacent to the weld, particularly the separator exposed relative to the two electrodes. If the separator is damaged, current may flow between the positive and negative electrodes.

[0082] In the present invention, as shown in FIG. 6, a separation distance can be secured between the welded portion of the battery outer material and the battery outer cap and the separator of the electrode assembly. Therefore, damage to the separator caused by heat generated during laser welding in the sealing step can be prevented.

[0083] One embodiment of the present invention provides a method for manufacturing a secondary battery, wherein the step of welding and sealing the battery outer cap is performed without damaging the separator of the electrode assembly.

[0084] One embodiment of the present invention provides an electrode assembly having a structure in which a first electrode, a second electrode, and a separator provided between the first electrode and the second electrode are wound, wherein a portion of the upper outermost part of the electrode assembly is bent in the direction of the winding center, and the difference between the longest diameter and the shortest diameter of the bent portion of the electrode assembly is 0.1 mm or more and 20 mm or less.

[0085] With respect to an electrode assembly having a structure in which the first electrode, the second electrode, and a separator provided between the first electrode and the second electrode are wound, the above-described details may be applied in the same way to the method of manufacturing the electrode assembly.

[0086] The term "outermost" above refers to the outermost sheet of the wound electrode assembly.

[0087] The statement that a portion is bent from the outermost angle toward the winding center means a shape in which a portion is bent from the outermost angle toward the winding center, including the outermost angle.

[0088] A portion from the outermost edge toward the center of the winding may be two or more sheets including the outermost sheet of the electrode assembly.

[0089] That is, it is a folded form that necessarily includes the outermost sheet of the electrode assembly, and two or more sheets are folded in the direction of the winding center.

[0090] The upper portion of the electrode assembly may include a range of at least 10 μm in a direction parallel to the winding center axis from the top of the electrode assembly.

[0091] That is, it may include a range up to 20 μm, a range up to 30 μm, a range up to 100 μm, a range up to 500 μm, a range up to 1 mm, and a range up to 10 mm.

[0092] As the upper portion of the electrode assembly is bent from the outermost edge toward the center of the winding, when the electrode assembly is inserted into a secondary battery, a separation distance can be secured between the laser welded portion of the sealing step and the separator of the electrode assembly. Therefore, damage to the separator caused by heat generated during laser welding in the sealing step can be prevented.

[0093] One embodiment of the present invention provides an electrode assembly in which the diameter of the bent portion of the electrode assembly decreases toward the top.

[0094] FIG. 2 is an electrode assembly (1) according to one embodiment of the present invention, in which the diameter of the upper bent portion becomes smaller as it goes toward the top.

[0095] The uppermost (11) is the uppermost surface among the surfaces perpendicular to the winding center axis. The diameter of the bent portion of the electrode assembly is the diameter of each surface perpendicular to the winding center axis (10).

[0096] At this time, the diameter (L) of the bent portion of the electrode assembly may be shaped to decrease as it approaches the top (11). The diameter (L) of the bent portion of the electrode assembly may decrease continuously or intermittently as it approaches the top (11). Additionally, a section where it decreases continuously and a section where it decreases intermittently may exist together.

[0097] One embodiment of the present invention provides an electrode assembly in which the angle formed between the bent portion of the electrode assembly and the winding center axis is 10° or more and 80° or less.

[0098] In another embodiment, the angle formed by the bent portion of the electrode assembly and the winding center axis may be 20° or more and 80° or less, 30° or more and 80° or less, 40° or more and 80° or less, and 50° or more and 70° or less.

[0099] FIG. 3 is a reference diagram for showing the shape of a bent portion (12) of an electrode assembly (1) according to one embodiment of the present invention in terms of angle.

[0100] The angle (θ) formed by the bent portion (12) of the electrode assembly and the winding center axis (10) refers to the acute angle formed at the point where the line (120) extending the molded portion (12) and the line extending the winding center axis (10) meet.

[0101] One embodiment of the present invention provides an electrode assembly in which the shortest diameter of the bent portion of the electrode assembly is 50% or more and 99% or less of the longest diameter.

[0102] In the electrode assembly (1) of FIG. 2, the longest diameter (L1) and the shortest diameter (L2) of the bent portion (12) are shown.

[0103] One embodiment of the present invention provides a secondary battery comprising an electrode assembly according to the present invention.

[0104] The above secondary battery includes an electrode assembly according to the present invention as described above, and the electrode assembly and electrolyte are accommodated inside the battery casing, and may further include a battery casing cap disposed in an opening of the battery casing.

[0105] With respect to the battery outer material, battery outer cap, and electrolyte, the above-described contents of the method for manufacturing the secondary battery can be applied in the same way.

[0106] Hereinafter, examples are provided to specifically explain the present specification. However, the examples according to the present specification may be modified in other forms, and the scope of the present application is not limited to the following examples. The examples of the present application are provided to more completely explain the present specification to those with average knowledge in the art.

[0108] <실시예 1>

[0109] An electrode assembly was prepared having a structure comprising an anode, a cathode, and a separator wound between the anode and the cathode. A portion of the upper outermost part of the electrode assembly, extending toward the center of the winding, was formed using a servo motor. The temperature condition was 80°C, and pressure was applied for 3 seconds.

[0110] FIG. 10 (a) is a top view of the formed electrode assembly, and FIG. 10 (b) is a side view of the formed electrode assembly. The longest diameter (L1) of the formed electrode assembly was 10.98 mm, and the shortest diameter (L2) was 8.98 mm. The angle (θ) between the line extending the formed portion and the line extending the winding center axis of the electrode assembly was measured to be 63°.

[0111] The above-mentioned molded electrode assembly was inserted into the battery casing, and an electrolyte was injected. Then, a battery casing cap was placed in the opening of the battery casing, and the joint between the battery casing and the battery casing cap was sealed by laser welding to manufacture a secondary battery.

[0112] At this time, the distance from the battery outer cap to the unfolded outermost sheet of the electrode assembly (b1 in FIG. 6) is 0.51 mm, and the distance from the battery outer cap to the top of the battery assembly (b2 in FIG. 6) is 0.21 mm, and the distance from the battery outer cap to the top of the battery assembly may be dependent on the thickness of the insulating tape. In addition, the distance from the side of the battery outer material to the top of the battery assembly (a1 in FIG. 6) is 1.1 mm, and the distance from the side of the battery outer material to the unfolded outermost sheet of the electrode assembly (a2 in FIG. 6) is 0.1 mm.

[0113] To check for damage to the separator, the manufactured secondary battery was disassembled.

[0114] Figure 11 shows the separator embedded in the secondary battery unfolded, and it was confirmed that it was not damaged by laser welding.

[0116] <실시예 2>

[0117] A secondary battery was manufactured in the same manner as in Example 1, except that the longest diameter (L1) of the molded electrode assembly is 2 mm and the shortest diameter (L2) is 1.8 mm, and the angle (θ) between the line extending the molded part and the line connecting the winding center axis of the electrode assembly is 63°. The manufactured secondary battery was disassembled to check the internal separator, and it was confirmed that the separator was not damaged.

[0119] <실시예 3>

[0120] A secondary battery was manufactured in the same manner as in Example 1, except that the longest diameter (L1) of the molded electrode assembly was 50 mm and the shortest diameter (L2) was 42 mm, and the angle (θ) between the line extending the molded part and the line connecting the winding center axis of the electrode assembly was 63°. The manufactured secondary battery was disassembled to check the internal separator, and it was confirmed that the separator was not damaged.

[0122] <비교예 1>

[0123] A secondary battery was manufactured in the same manner as in Example 1, except that the electrode assembly according to the present invention was not molded. FIG. 7 is a cross-section of a secondary battery according to Comparative Example 1, and it can be seen that the separator of the electrode assembly at the welded portion of the battery outer material and the battery outer cap is damaged.

[0124] Figure 8 shows the upper part of the electrode assembly after removing the battery outer cap of the secondary battery according to Comparative Example 1, and it can be seen that the separator of the welded part is also damaged. Figure 9 shows an enlarged view of the separator of the electrode assembly inside the secondary battery according to Comparative Example 1, and it can be seen that the separator is damaged up to a maximum range of 600 μm.

[0125] Ultimately, since the electrode assembly according to the present invention is formed such that a portion from the upper outermost edge toward the winding center is bent toward the winding center, when the electrode assembly is inserted into a secondary battery, a separation distance can be secured between the laser welded portion of the sealing step and the separator of the electrode assembly. Therefore, damage to the separator caused by heat generated during laser welding in the sealing step can be prevented, thereby improving the safety of the secondary battery. Explanation of the symbols

[0126] 1: Electrode assembly 10: Winding center axis 11: Top 12: Formed or bent parts L: Diameter L1: Longest diameter L2: Shortest diameter 120: Line extending from the formed or bent part 100: Line extending the central axis of the winding 2: Battery external cap 3: Servo motor 4: Insulator 5: Battery casing a1: Distance from the side of the battery casing to the top of the electrode assembly a2: Distance from the side of the battery casing to the unfolded outermost sheet of the electrode assembly b1: Distance from the battery outer cap to the unfolded outermost sheet of the electrode assembly b2: Distance from the battery outer cap to the top of the electrode assembly θ: The angle between the line extending the formed or folded portion and the line extending the winding center axis.

Claims

Claim 1 A method for manufacturing an electrode assembly comprising: a step of preparing an electrode assembly having a structure in which a first electrode, a second electrode, and a separator provided between the first electrode and the second electrode are wound; and a step of forming a portion of the upper outermost part of the electrode assembly in the direction of the winding center into a shape bent in the direction of the winding center, wherein the forming step is formed such that the difference between the longest diameter and the shortest diameter of the formed portion of the electrode assembly is 0.1 mm or more and 20 mm or less. Claim 2 A method for manufacturing an electrode assembly according to claim 1, wherein a portion from the outermost edge toward the winding center is two or more sheets including the outermost sheet of the electrode assembly. Claim 3 A method for manufacturing an electrode assembly according to claim 1, wherein the upper portion of the electrode assembly comprises a range of at least 10 μm in a direction parallel to the winding center axis from the uppermost portion of the electrode assembly. Claim 4 A method for manufacturing an electrode assembly according to claim 1, wherein the molding step is molding at 40°C to 120°C. Claim 5 A method for manufacturing an electrode assembly according to claim 1, wherein the forming step is to form the electrode assembly such that the diameter of the formed portion of the electrode assembly becomes smaller toward the top. Claim 6 A method for manufacturing an electrode assembly according to claim 1, wherein the forming step is to form the electrode assembly such that the angle formed by the formed portion of the electrode assembly and the winding center axis is 10° or more and 80° or less. Claim 7 A method for manufacturing an electrode assembly according to claim 1, wherein the forming step is to form the shortest diameter of the formed portion of the electrode assembly to be 50% or more and 99% or less of the longest diameter. Claim 8 A method for manufacturing a secondary battery comprising the steps of: inserting an electrode assembly manufactured according to any one of claims 1 to 7 into a battery casing; injecting an electrolyte into the battery casing; placing a battery casing cap in an opening of the battery casing; and welding and sealing the battery casing cap. Claim 9 A method for manufacturing a secondary battery according to claim 8, wherein the difference between the distance from the battery outer cap to the outermost unfolded sheet of the electrode assembly and the distance from the battery outer cap to the top of the electrode assembly is 10 μm to 10 mm, and the difference between the distance from the side of the battery outer material to the top of the electrode assembly and the distance from the side of the battery outer material to the outermost unfolded sheet of the electrode assembly is 0.05 mm to 5 mm. Claim 10 A method for manufacturing a secondary battery according to claim 8, wherein the step of welding and sealing the battery outer cap is to perform welding without damaging the separator of the electrode assembly. Claim 11 An electrode assembly having a structure in which a first electrode, a second electrode, and a separator provided between the first electrode and the second electrode are wound, wherein a portion of the upper outermost part of the electrode assembly in the direction of the winding center is bent in the direction of the winding center, and the difference between the longest diameter and the shortest diameter of the bent portion of the electrode assembly is 0.1 mm or more and 20 mm or less. Claim 12 An electrode assembly according to claim 11, wherein a portion from the outermost edge toward the winding center is two or more sheets including the outermost sheet of the electrode assembly. Claim 13 An electrode assembly according to claim 11, wherein the upper portion of the electrode assembly comprises a range of at least 10 μm in a direction parallel to the winding center axis from the uppermost portion of the electrode assembly. Claim 14 An electrode assembly according to claim 11, wherein the diameter of the bent portion of the electrode assembly decreases toward the top. Claim 15 An electrode assembly according to claim 11, wherein the angle formed by the bent portion of the electrode assembly and the winding center axis is 10° or more and 80° or less. Claim 16 An electrode assembly according to claim 11, wherein the shortest diameter of the bent portion of the electrode assembly is 50% or more and 99% or less of the longest diameter. Claim 17 A secondary battery comprising an electrode assembly according to any one of claims 11 to 16.

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