Electrode assembly and secondary battery including the same

Abstract

An electrode assembly and a secondary battery including the same are provided, the electrode assembly including a positive electrode, a negative electrode, and a separator disposed between the positive electrode and the negative electrode, the wet adhesive strength of the separator to the negative electrode being 1.5 gf / 20 mm or more and 15 gf / 20 mm or less. When the wet adhesive strength of the separator of the electrode assembly to the negative electrode satisfies the above range, distortion of the electrode assembly is effectively prevented before impregnation with an electrolyte, and bending phenomenon after activation of the electrode assembly and the secondary battery including the same can be more effectively suppressed after impregnation with an electrolyte.

Description

[Technical Field]

[0001] [CROSS-REFERENCE TO RELATED APPLICATIONS] This application claims the benefit of the filing date of Korean Patent Applications Nos. 10-2022-0177177, 10-2022-0177190, and 10-2022-0177156, filed on December 16, 2022, and all contents disclosed in the documents of those Korean patent applications are incorporated herein by reference.

[0002] The present invention relates to an electrode assembly and a secondary battery including the same. [Background technology]

[0003] Secondary batteries are divided into coin-type batteries, cylindrical batteries, prismatic batteries, pouch-type batteries, etc. depending on the shape of the battery case. Unlike primary batteries, they can be recharged, and there is growing potential for them to be made smaller and have larger capacities, so much research and development has been done on them in recent years.

[0004] Recently, as electric vehicles (EVs) have become more popular, technological development and demand for high-capacity secondary batteries for use in EVs has increased. To manufacture high-capacity secondary batteries, the size of electrode assemblies mounted inside battery cases has also increased. When the size of an electrode assembly is large, problems that were not anticipated when using smaller electrode assemblies may occur.

[0005] The electrode assembly is a power generating element that can be charged and discharged, and is made up of a laminated structure of electrodes and separators. The separators contain an organic / inorganic composite porous coating layer, which provides adhesion between the electrodes and separator. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Korean Patent Publication No. 10-2013-0132230 Summary of the Invention [Problem to be solved by the invention]

[0007] The electrode assembly is installed inside a battery case and then undergoes a packaging process and / or activation process to manufacture a secondary battery. However, when the negative electrode contains a silicon-based active material, the expansion rate of the negative electrode is greater than that of the positive electrode before and after the activation process, which can cause variations in the adhesive strength between the separator and the electrode, resulting in a bending phenomenon in which the electrode assembly warps or bends, and this can cause problems with the shape of the secondary battery itself.

[0008] In particular, when the size of an electrode assembly is large, such as in a large-capacity electrode assembly, the difference in the expansion rate between the negative electrode and the positive electrode becomes even more significant, which can cause a significant bending problem. Therefore, there is a need for technological development to prevent bending in a large-capacity electrode assembly or a secondary battery including the same. [Means for solving the problem]

[0009] One embodiment of the present invention provides an electrode assembly including a positive electrode, a negative electrode, and a separator disposed between the positive electrode and the negative electrode, wherein the wet adhesive strength of the separator to the negative electrode is 1.5 gf / 20 mm or more and 15 gf / 20 mm or less.

[0010] One embodiment of the present invention provides a secondary battery including a sealed battery case, an electrode assembly according to the above embodiment contained inside the battery case, and an electrolyte solution contained inside the battery case, and satisfying the following formula 1:

[0011] [Formula 1] X<5mm In the formula 1, X is, after the activation step of the secondary battery, formed by bending the electrode assemblyIt means the maximum distance measured from an imaginary reference line connecting two opposing sides of the upper surface of the secondary battery to the lowest point on the upper surface of the secondary battery when the secondary battery is placed on a flat surface with the concave side of the secondary battery facing up. [Effects of the Invention]

[0012] The electrode assembly according to an embodiment of the present invention is effective in preventing bending that may occur after activation of a secondary battery including the electrode assembly, particularly in a large-sized electrode assembly.

[0013] The electrode assembly according to the embodiment of the present invention can prevent bending, thereby preventing process defects after battery activation and improving assembly yield. Furthermore, the electrode can be fixed without misalignment, which leads to improved energy density.

[0014] A secondary battery including an electrode assembly according to an embodiment of the present invention can prevent bending, thereby improving assembly yield after activation, maintaining good electrode alignment, and preventing degradation of cell performance. [Brief explanation of the drawings]

[0015] [Figure 1] 1 is a schematic cross-sectional view of a separator according to a specific embodiment of the present invention. [Figure 2] 1 shows an image of the surface of a separator according to a specific embodiment of the present invention. [Figure 3] 10A and 10B are diagrams illustrating that problems due to bending can be exacerbated in the case of a large-area electrode assembly. [Figure 4] 1 is a diagram showing one method for measuring bending of an electrode assembly according to the present application. [Figure 5] 1 is a diagram schematically illustrating a separator according to the present invention. [Figure 6]3A to 3C are cross-sectional views illustrating a process flow of an electrode assembly manufacturing apparatus according to an embodiment of the present invention. [Figure 7] 1 is a plan view showing a process flow of an electrode assembly manufacturing apparatus according to an embodiment of the present invention; [Figure 8] 1 is a cross-sectional view illustrating an example of an electrode assembly manufactured by an electrode assembly manufacturing apparatus and an electrode assembly manufacturing method according to an embodiment of the present invention; [Figure 9] 1(a) is a perspective view showing the first heat press unit 50, and FIG. 1(b) is a perspective view showing the second heat press unit 60. FIG. [Figure 10] 1 is an image taken to check whether or not there are wrinkles in the separator of the electrode assembly according to Example 1. [Figure 11] 10 is an image taken to check whether or not there are wrinkles in the separator of the electrode assembly according to Comparative Example 14. [Figure 12] 10 is an image taken to confirm the meandering nature of the electrode assembly according to Example 1. [Figure 13] 10 is an image taken to confirm the meandering nature of the electrode assembly according to Comparative Example 11. DETAILED DESCRIPTION OF THE INVENTION

[0016] While the present invention may be embodied in many different forms and should not be construed as limited to the embodiments set forth herein, the present invention will be described in detail below so that those skilled in the art can easily practice the present invention.

[0017] In this specification, when a part is said to "comprise" a certain component, this means that it may further include other components, rather than excluding other components, unless specifically stated to the contrary.

[0018] In this specification, the "area" of an electrode assembly refers to the area of ​​a surface that can be seen when the electrode assembly is viewed from above in the stacking direction of the electrodes and separators included in the electrode assembly, i.e., the area of ​​the electrode assembly surface that is perpendicular to the stacking axis.

[0019] As used herein, the term "dry adhesive strength" refers to the adhesive strength of a separator measured when the electrode assembly including the separator is not immersed in an electrolyte. That is, it refers to the adhesive strength of a separator measured before the activation step of the electrode assembly. As used herein, the term "dry adhesive strength" also refers to the adhesive strength of a separator in a dry state.

[0020] As used herein, the term "wet adhesive strength" refers to the adhesive strength of a separator measured when an electrode assembly including the separator is immersed in an electrolyte. That is, it may refer to the adhesive strength of a separator measured after activation of the electrode assembly or after charging and discharging the battery. As used herein, the term "wet adhesive strength" also refers to the adhesive strength of a separator when immersed in an electrolyte.

[0021] In this specification, the dry adhesive strength and wet adhesive strength can be measured by cutting the electrode assembly into a 20 mm x 70 mm test piece in which the positive electrode, separator, and negative electrode are stacked. The separator of the test piece is then peeled from one side of the separator in a 90° peel mode using a tensile tester (UTM equipment) at a rate of 100 mm / min. The peel direction is the longitudinal direction of the test piece (parallel to the 70 mm side). That is, the methods for measuring the dry adhesive strength and wet adhesive strength are the same, except for whether the electrode assembly is impregnated with an electrolyte. The absolute value of the difference between the measured adhesive strengths can be defined as the adhesive strength deviation.

[0022] In this specification, the term "activation" or "activation process" of a secondary battery refers to a process (or step) of activating the secondary battery through a charging process and removing gas.

[0023] <Electrode assembly> One embodiment of the present invention provides an electrode assembly in which the separator has a certain degree of wet adhesion to the negative electrode. That is, the electrode assembly according to the present invention has a certain degree of wet adhesion to the negative electrode even after being immersed in an electrolyte. The adhesion between the separator and the negative electrode can be affected by the type and physical properties of the separator, the material of the coating layer on the separator surface, the lamination conditions and activation conditions of the electrode assembly, and the material of the negative electrode. For example, the wet or dry adhesion to the negative electrode can vary depending on the type, physical properties, or material of the separator. Furthermore, the wet or dry adhesion between the separator and the negative electrode can vary depending on the conditions applied during the lamination process of the positive electrode, negative electrode, and separator of the electrode assembly and / or the activation conditions of the secondary battery. Furthermore, the degree of expansion or bending of the negative electrode during charge and discharge of the secondary battery can vary depending on the material of the negative electrode, which can affect the wet or dry adhesion between the separator and the negative electrode.

[0024] In one embodiment of the present invention, the wet adhesive strength of the separator to the negative electrode is 1.5 gf / 20 mm or more and 15 gf / 20 mm or less. For example, the wet adhesive strength of the separator to the negative electrode may be 2 gf / 20 mm or more, 2.5 gf / 20 mm or more, 3 gf / 20 mm or more, 3.5 gf / 20 mm or more, or 4 gf / 20 mm or more. The wet adhesive strength of the separator to the negative electrode may be 15 gf / 20 mm or less, 12 gf / 20 mm or less, 10 gf / 20 mm or less, 8 gf / 20 mm or less, 7 gf / 20 mm or less, 6 gf / 20 mm or less, or 5 gf / 20 mm or less.

[0025] When the wet adhesive strength satisfies the above range, the wet adhesive strength of the separator to the negative electrode is at least a certain value, which not only serves to fix the separator and the negative electrode but also prevents bending of the electrode assembly during an activation process of a secondary battery including the electrode assembly because the wet adhesive strength is not excessive, thereby improving the performance of the secondary battery.

[0026] In one embodiment of the present invention, the dry adhesive strength of the separator to the negative electrode may be 8 gf / 20 mm or more, 10 gf / 20 mm or more, 12 gf / 20 mm or more, 14 gf / 20 mm or more, or 15 gf / 20 mm or more. The dry adhesive strength of the separator to the negative electrode may be 25 gf / 20 mm or less, 23 gf / 20 mm or less, 20 gf / 20 mm or less, or 18 gf / 20 mm or less. When the dry adhesive strength satisfies the above range, the stacked structure of the electrode assembly manufactured in the stacking process can be more easily transported while maintaining its stacked structure. That is, deterioration in performance of the electrode assembly due to electrode misalignment during transportation can be prevented, resulting in improved performance of the manufactured electrode assembly. Furthermore, the lack of excessive dry adhesive strength is advantageous for maintaining an appropriate level of wet adhesive strength after electrolyte impregnation.

[0027] In one example, the wet adhesive strength may be 40% or less, 35% or less, or 33% or less of the dry adhesive strength. In other examples, the wet adhesive strength may be 10% or more, 15% or more, 20% or more, or 25% or more of the dry adhesive strength. When the wet adhesive strength of the separator of the electrode assembly to the negative electrode satisfies the above range, it is possible to effectively prevent misalignment of the electrode assembly before impregnation with an electrolyte solution, and after impregnation with an electrolyte solution, it is possible to more effectively suppress bending after activation of the electrode assembly and a secondary battery including the same. Specifically, while a strong dry adhesive strength is required to maintain the laminated structure of the electrode assembly during the stacking process, a wet adhesive strength within the above range may be too strong, which may further accelerate bending due to the difference in expansion coefficient between the negative electrode and the positive electrode.

[0028] According to one embodiment, the negative electrode contains a silicon-based active material. In this case, the negative electrode has a higher expansion rate after activation than a positive electrode that does not contain a silicon-based active material. If the adhesive strength does not satisfy the above range, the expansion of the negative electrode and the difference in the expansion rates between the negative electrode and the positive electrode cause variations in adhesive strength between the separator and the electrode, resulting in a bending phenomenon in which the electrode assembly warps or bends.

[0029] However, in the electrode assembly according to the present invention, since the separator of the electrode assembly has a certain degree of dry adhesive strength and wet adhesive strength to the negative electrode, it is possible to prevent distortion of the stacked structure of the electrodes and separator included in the electrode assembly during the manufacturing process of the electrode assembly, while minimizing the occurrence of uneven adhesion between the electrodes and separator due to expansion of the negative electrode and the difference in expansion rates between the negative electrode and the positive electrode. In other words, it is possible to simultaneously prevent distortion of the stacked structure of the electrodes and separator during the stacking process and bending after bending activation.

[0030] In one embodiment of the present invention, the separator comprises: , in particular, the surface component of the layer provided on the negative electrode side of the separatorThe separator may contain 0.1 parts by weight or more, 2 parts by weight or more, 3 parts by weight or more, or 4 parts by weight or more of fluorine (F) per 100 parts by weight of the separator surface component. The separator may contain 8 parts by weight or less, 6 parts by weight or less, or 5 parts by weight or less of fluorine (F) per 100 parts by weight of the separator surface component.

[0031] In this specification, the surface of the separator can be observed by photographing the surface of the separator using a scanning electron microscope (SEM). The term "separator surface components" refers to components measured in a portion (hereinafter, "separator surface") of the separator, which is obtained by disassembling the secondary battery after activation and then immersing the separator in a dimethyl carbonate solvent for 30 minutes to remove any electrolyte additives or metal salt components remaining on the surface, and then drying the separator at room temperature for 24 hours, at which the organic / inorganic composite porous coating layer is formed, using a scanning electron microscope (SEM) at an accelerating voltage of 15.0 kV and a magnification of 10,000, as shown in FIG. 2.

[0032] More specifically, the components measured by analyzing the separator surface using energy dispersive X-ray spectroscopy (EDS) are defined as the separator surface components, and the sum of the components measured by the EDS analysis, i.e., the total elements contained in the visible portion of the SEM image, can be defined as 100 parts by weight. In this case, the surface component analysis using EDS can be carried out while taking images at 15 kV and 10,000x magnification.

[0033] That is, the content of fluorine (F) in the separator is 0.1 to 8 parts by weight based on 100 parts by weight of the surface component of the separator, means that the relative content of fluorine in the separator is 0.1 to 8 parts by weight based on 100 parts by weight.

[0034] The separator containing fluorine (F) in the above range per 100 parts by weight of the separator surface components means that the separator contains a fluorine-based binder even before being immersed in an electrolyte. The presence of the fluorine-based binder allows the separator to have adhesive strength (dry adhesive strength) to the electrode even before the electrode assembly according to the present invention is immersed in an electrolyte. In addition, the separator surface containing fluorine in the above amount means that the dry adhesive strength of the electrode assembly can be within the above range.

[0035] In one embodiment of the present invention, the separator may be folded and stacked in a zigzag pattern, that is, the electrode assembly according to one embodiment of the present invention may be zigzag stacked.

[0036] In this specification, stacking the positive electrode and the negative electrode alternately between the folded separator is referred to as zigzag stacking.

[0037] In this regard, the configuration in which the positive electrode and the negative electrode are alternately arranged between the folded separators may be described in more detail as a separator in which the separators are stacked in a zigzag pattern. More specifically, the separators are stacked in a zigzag pattern while being folded alternately from the left side of the stacking axis to the right side of the stacking axis. The stacking axis refers to a virtual axis that is parallel to the stacking direction of the positive electrode, separator, and negative electrode and passes through the center of the stacked electrode and separator.

[0038] That is, the positive electrodes and the negative electrodes are alternately arranged between the separators means that the separators are stacked in a zigzag pattern in the direction of the stacking axis, and one positive electrode and one negative electrode are alternately inserted into the spaces (between the separators) that are generated as the separators are stacked.

[0039] To perform zig zag stacking, techniques or devices commonly used in the art can be used.

[0040] In an embodiment of the present invention, the electrode assembly may have a rated capacity of 50 Ah to 200 Ah, preferably 50 Ah to 150 Ah, and more preferably 60 Ah to 140 Ah.

[0041] In one embodiment of the present invention, the wet adhesive strength of the separator to the negative electrode may be greater than the wet adhesive strength of the separator to the positive electrode.

[0042] In one embodiment of the present invention, the wet adhesive strength of the separator to the negative electrode may be 1 or more times, 1.1 or more times, or 1.2 or more times the wet adhesive strength of the separator to the positive electrode. The wet adhesive strength of the separator to the negative electrode may be less than 1.5 times, or 1.4 or less times the wet adhesive strength of the separator to the positive electrode.

[0043] For example, the difference between the wet adhesive strength of the separator to the negative electrode and the wet adhesive strength of the separator to the positive electrode may be 5 gf / 20 mm or less, 3 gf / 20 mm or less, 1.5 gf / 20 mm or less, or 1.2 gf / 20 mm or less, where the difference refers to the absolute value of the difference in adhesive strength.

[0044] As described above, the wet adhesive strength is measured in a state where the electrode assembly is immersed in an electrolyte solution, and the smaller the difference in wet adhesive strength, the less likely the bending effect is to occur, which is preferable.

[0045] In one embodiment of the present invention, the dry adhesive strength of the separator to the negative electrode may be greater than the dry adhesive strength of the separator to the positive electrode.

[0046] For example, the dry adhesive strength of the separator to the negative electrode may be at least 1 or 1.1 times the dry adhesive strength of the separator to the positive electrode, and the dry adhesive strength of the separator to the negative electrode may be at most 2.5, 2, 1.5, or 1.3 times the dry adhesive strength of the separator to the positive electrode.

[0047] In one embodiment of the present invention, the difference between the dry adhesive strength of the separator to the negative electrode and the dry adhesive strength of the separator to the positive electrode may be 10 gf / 20 mm or less, 8 gf / 20 mm or less, 7 gf / 20 mm or less, 5 gf / 20 mm or less, 4 gf / 20 mm or less, or 3 gf / 20 mm or less, where the difference refers to the absolute value of the difference in adhesive strength.

[0048] The smaller the difference in dry adhesive strength, the less the difference in wet adhesive strength can be controlled in the processes following the stacking process.

[0049] In one embodiment of the present invention, the upper surface of the electrode assembly may have a rectangular shape having short and long sides, and the ratio of the length of the long side to the length of the short side may be 3 to 12. The rectangular shape refers to the electrode assembly as viewed in the stacking direction.

[0050] In one embodiment of the present invention, the area of ​​the electrode assembly is 500 cm 2 It may be more than that.

[0051] In one embodiment of the present invention, the electrode assembly may have a total length of 400 mm or more and a total width of 50 mm or more.

[0052] More specifically, in one embodiment of the present invention, one surface of the electrode assembly may be rectangular having short and long sides, with a total length of 400 mm to 600 mm and a total width of 50 mm to 150 mm.

[0053] An electrode assembly having the above size may also be defined as a large-area electrode assembly in this specification.

[0054] In one embodiment of the present invention, the total length of the electrode assembly refers to the length of the long side of the electrode assembly, and refers to the length in a direction perpendicular to the supply direction of the separator supplied during the manufacture of the electrode assembly.

[0055] In the case of an electrode assembly with a large number of stacked electrodes and a total length of 400 mm or more, the difference in the expansion rates of the negative and positive electrodes has a greater impact, which can lead to greater problems due to bending or warping of the electrode assembly.

[0056] As shown in Figure 3, even for the same angle c, the greater the distance from the reference point, the greater the distance from the horizontal. That is, if a small electrode assembly is bent or warped by angle c, and the distance from the horizontal to the edge of the electrode assembly is a, then for a large electrode assembly, the distance from the horizontal to the edge of the electrode assembly under the same conditions will be b. That is, it can be seen that the distance from the horizontal to the edge of the electrode assembly is greater for a large electrode assembly, which means that problems due to bending can occur more severely in the case of a large electrode assembly.

[0057] That is, even if the electrode assembly is warped or sagged at the same angle, the bending phenomenon may be a relatively greater problem when the electrode assembly is large than when the electrode assembly is small.

[0058] Also, even if the electrode assembly is heated and pressed to be manufactured flat, due to the large number of stacked electrodes, there is a problem of shrinkage and expansion, and there are limitations. However, in the case of the present invention, by satisfying the conditions such as the adhesive force of the separator described above, bending of the secondary battery can be prevented after the activation process.

[0059] In one embodiment of the present invention, the negative electrode contains a silicon-based active material. The silicon-based active material may contain at least one of a silicon-carbon composite and a silicon oxide. For example, the silicon-based active material may contain a silicon-carbon composite, a silicon oxide, or both. The silicon-based oxide is a material containing SiOx (0 < x < 2). The negative electrode may further contain a carbon-based active material. Graphite can be used as the carbon-based active material. For example, the negative electrode may contain 1 to 40 parts by weight, 2 to 30 parts by weight, 3 to 15 parts by weight, or 4 to 10 parts by weight of the silicon-based active material out of 100 parts by weight of the active material.

[0060] In one embodiment of the present invention, the negative electrode includes a negative electrode current collector; and a negative electrode active material layer located on at least one surface of the negative electrode current collector and containing a negative electrode active material, a binder, and a conductive material. The negative electrode active material layer consists of a lower layer region that is in surface contact with the negative electrode current collector and an upper layer region that extends to the surface of the negative electrode active material while being in surface contact with the lower layer region. At least one of the lower layer region and the upper layer region may contain a silicon-based active material. If necessary, both the lower layer region and the upper layer region may contain a silicon-based active material. At least one of the lower layer region and the upper layer region may further contain a carbon-based active material.

[0061] Here, "surface contact" means a form in which surface and surface are in contact.

[0062] In one embodiment of the present invention, the separator may include a porous substrate and an organic / inorganic composite porous coating layer formed on at least one surface of the porous substrate. In the electrode assembly according to the present invention, the separator must have adhesive strength to the negative electrode, and therefore, one surface of the separator may be in contact with the negative electrode.

[0063] In one embodiment of the present invention, the separator may include a porous substrate and an organic / inorganic composite porous coating layer formed on at least one surface of the porous substrate. That is, one surface of the separator contacts the negative electrode, and the other surface of the separator contacts the positive electrode. When the organic / inorganic composite porous coating layer is formed on both surfaces of the separator, the separator may have adhesive strength to the negative electrode and the positive electrode, respectively.

[0064] In one embodiment of the present invention, the organic / inorganic composite porous coating layer may contain one or more types of particulate binder resins and one or more types of inorganic particles.

[0065] Specifically, FIG. 1 is a schematic cross-sectional view of a separator according to one embodiment of the present invention, in which separator 14 includes a porous substrate 1 and an organic / inorganic composite porous coating layer 2 formed on at least one surface of the porous substrate. While FIG. 1 shows organic / inorganic composite porous coating layer 2 formed on only one surface of porous substrate 1, organic / inorganic composite porous coating layer 2 of the separator of the present invention may also be formed on the other surface of porous substrate 1. Organic / inorganic composite porous coating layer 2 includes particulate binder resins 4 and 5 and inorganic particles 3. As will be described later, particulate binder polymers 4 and 5 may be fluoropolymers 4 and acrylic polymers 5, respectively.

[0066] In one embodiment of the present invention, the particulate binder resin may include an acrylic polymer and a fluorine-based polymer.

[0067] In one example, the weight ratio of the acrylic polymer to the fluoropolymer may be 20:80 to 60:40. The fluoropolymer may affect wet adhesion. The separator surface acts as an adhesive layer with the electrode, but excessive acrylic polymer on the separator surface can reduce wet adhesion. For example, when the acrylic polymer has a particle size of 350 nm to 450 nm and a density of 1.4 to 1.6, and the fluoropolymer has a particle size of 250 nm to 400 nm and a density of 1.6 to 1.8, the difference between emulsion particle size and density favors migration of the acrylic polymer to the separator surface through surface migration. Therefore, it is preferable to adjust the content of the acrylic polymer to 60 parts by weight or less, as described above. Furthermore, when the acrylic polymer is less than 20 parts by weight, dry adhesion is reduced, maintaining strong adhesion between the positive electrode and separator, while the adhesion between the negative electrode and separator is relatively reduced, potentially resulting in bending defects.

[0068] In one embodiment of the present invention, the fluoropolymer may be a homopolymer of vinylidene fluoride (PVDF), a copolymer of vinylidene fluoride and another polymerizable monomer, or a mixture of two or more thereof.

[0069] More specifically, the vinylidene fluoride and other polymerizable monomers may include, but are not limited to, one or more selected from the group consisting of tetrafluoroethylene, hexafluoropropylene, trifluoroethylene, chlorofluoroethylene, 1,2-difluoroethylene, perfluoro(methyl vinyl) ether, perfluoro(ethyl vinyl) ether, perfluoro(propyl vinyl) ether, perfluoro(1,3-dioxole), perfluoro(2,2-dimethyl-1,3-dioxole), trichloroethylene, and vinyl fluoride. In particular, the fluoropolymer may be a copolymer of vinylidene fluoride and hexafluoropropylene (HFP) (PVdF-HFP). The content of vinylidene fluoride and other polymerizable monomers may be 1% by weight to 20% by weight, preferably 3% by weight to 18% by weight, of the copolymer. The other polymerizable monomer is used to enhance wet adhesion. If the content is less than 1 wt %, wet adhesion may be difficult to achieve. If the content exceeds this range, the separator resistance may be too high, resulting in reduced performance of the electrode assembly. For example, the fluoropolymer may be a copolymer of vinylidene fluoride and hexafluoropropylene (HFP) (PVdF-HFP), and the hexafluoropropylene may be present in an amount of 3 to 18 parts by weight per 100 parts by weight of the comonomers constituting the copolymer (PVdF-HFP). When the content of HFP is 3 parts by weight or more, a certain level of wet adhesion can be achieved, and when the content is 18 parts by weight or less, bending due to excessive adhesion can be prevented. If the separator and electrode have an excessively high wet adhesive strength, the difference between the dry and wet adhesive strength of the separator to the negative electrode is greater than the difference between the dry and wet adhesive strength of the separator to the positive electrode, which can lead to bending.If the adhesive strength between the separator and electrode is too high, the binder in the separator may hinder the diffusion and wettability of the electrolyte, degrading electrolyte impregnation and increasing internal resistance.

[0070] In the present invention, the comonomer content in the PVDF-based polymer can be measured by H-NMR using a Varian 500 MHz NMR. For details of the measurement method, see Journal of Materials Chemistry, 2012, 22, 341 or AMT-3412-0k. The NMR spectrum can be confirmed using appropriate equipment, such as a Bruker Avance III HD 700 MHz NMR or a Varian 500 MHz NMR.

[0071] In the present invention, the acrylic polymer may preferably be a (meth)acrylic acid ester-styrene copolymer or an acrylic-styrene copolymer. Specific examples of such (meth)acrylic acid esters include methyl (meth)acrylate, ethyl (meth)acrylate, n-propyl (meth)acrylate, i-propyl (meth)acrylate, n-butyl (meth)acrylate, i-butyl (meth)acrylate, n-amyl (meth)acrylate, i-amyl (meth)acrylate, hexyl (meth)acrylate, cyclohexyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, n-octyl (meth)acrylate, nonyl (meth)acrylate, and (meth)acrylate. Examples of suitable acrylates include decyl acrylate, hydroxymethyl (meth)acrylate, hydroxyethyl (meth)acrylate, ethylene glycol (meth)acrylate, ethylene glycol di(meth)acrylate, propylene glycol di(meth)acrylate, trimethylolpropane tri(meth)acrylate, pentaerythritol tetra(meth)acrylate, dipentaerythritol hexa(meth)acrylate, allyl (meth)acrylate, and ethylene di(meth)acrylate, and one or more selected from these may be used. Among these, one or more selected from methyl (meth)acrylate, ethyl (meth)acrylate, butyl (meth)acrylate, and 2-ethylhexyl (meth)acrylate are preferred, with butyl (meth)acrylate being particularly preferred.

[0072] More specifically, the acrylic-styrene copolymer may contain an acrylic binder, and the acrylic binder may be a polyacrylate. For example, the binder may be at least one selected from the group consisting of styrene-butadiene rubber, nitrile-butadiene rubber, acrylonitrile-butadiene rubber, acrylonitrile-butadiene-styrene rubber, and acrylate-based polymers, and more specifically, may be a copolymer containing acrylate.

[0073] In one example, the acrylic polymer is a (meth)acrylic acid ester-styrene copolymer, and the styrene may be present in an amount of 50 to 80 parts by weight per 100 parts by weight of the comonomer constituting the acrylic polymer. Styrene has relatively high crystallinity and a high melting temperature (Tm) compared to (meth)acrylic acid esters, such as butyl acrylate, and therefore, when present in a certain amount during copolymerization, it can affect dry adhesive strength. If the styrene content is less than 50 parts by weight, the Tg decreases, which can lead to melt deformation of the acrylic polymer during the separator drying process, resulting in lower than expected dry adhesive strength. If the styrene content exceeds 80 parts by weight, the acrylic polymer maintains its shape due to its high crystallinity, but its stickiness is relatively reduced.

[0074] In one embodiment of the present invention, the acrylic polymer particles may have a glass transition temperature (Tg) of 40°C to 60°C.

[0075] In one embodiment of the present invention, the inorganic particles may have a non-rectangular structure. When inorganic particles satisfying this structure are used, the separator has appropriate air permeability without interfering with the adhesive strength of the separator. The inorganic particles may have a D50 of 0.1 μm to 1 μm. The non-rectangular structure may have an aspect ratio of 1 to 10.

[0076] Specifically, in one embodiment of the present invention, the inorganic particles may be Al2O3.

[0077] According to one embodiment, the modulus of the separator measured in the separator feed direction (MD) is 4,000 kgf / cm 2 More than 10,000kgf / cm 2 Less than or 5,000 kgf / cm 2 More than 8,000kgf / cm 2 The separator has a modulus of elasticity of less than 0.1 and a kinetic friction coefficient of 0.15 to 0.33, or 0.2 to 0.3. FIG. 5 is a schematic diagram of a separator according to the present invention. The direction perpendicular to the short side w of the separator 14, the length of the long side of the separator 14, corresponds to the feeding direction MD of the separator 14. In this case, the separator may have the above-described modulus and kinetic friction coefficient. These modulus and kinetic friction coefficient not only affect the wet or dry adhesive strength to the positive or negative electrode, but also reduce the occurrence of separator wrinkles or misalignment defects during the stacking process of the electrode assemblies. Reducing these problems is even more important when the size of the electrode assembly increases, such as in a large-capacity electrode assembly. Therefore, by preventing wrinkles and maintaining alignment in a large-capacity electrode assembly, an electrode assembly with uniform and excellent performance can be provided. The short side length of the separator may be 500 mm or more, preferably 600 mm or more. The length of the short side of the separator may be the length of the long side of the electrode assembly, that is, the length of the short side of the separator means the length in a direction perpendicular to the feed direction of the separator.

[0078] In this specification, the length of the short side of the porous substrate is equal to the length of the short side of the separator, and the length of the short side of the separator refers to the side perpendicular to the separator feeding direction (MD; Machine Direction). As described below, the short side can be expressed as width.

[0079] The modulus of the separator may be a value measured in the separator feeding direction (MD; Machine Direction).

[0080] In one embodiment of the present invention, the separator has a modulus of 4,000 kgf / cm measured in the separator feeding direction (MD; Machine Direction). 2 ~30,000kgf / cm 2 , preferably 5,000 kgf / cm 2 ~30,000kgf / cm 2 , more preferably 5,500 kgf / cm 2 ~28,000kgf / cm 2 may be.

[0081] In this specification, the modulus of the separator was measured by preparing a separator specimen having a width of 15 mm and a length of 15 cm and performing a tensile test on the separator specimen using a Universal Testing Machine (UTM). More specifically, the speed condition of the Universal Testing Machine was set to 50 mm / min, and the test was performed, and the modulus was measured as the load applied when the separator specimen was deformed by 2% in the longitudinal direction. That is, here, the longitudinal direction refers to the MD direction of the separator, and the width refers to the length of the short side of the separator.

[0082] In one embodiment of the present invention, the separator may have a kinetic friction coefficient of more than 0.1 and not more than 0.35, for example, not less than 0.2 and not more than 0.3.

[0083] In this specification, the kinetic friction coefficient of the separator was measured using a Heidon 14FW friction / wear tester for the separator test piece, using a 0.1 mmR diamond pin with a weight of 5 g and a speed of 50 mm / min.

[0084] When the modulus and coefficient of kinetic friction of the separator satisfy the above conditions and ranges, an electrode assembly with excellent performance can be manufactured using the separator. Specifically, the occurrence of wrinkles and misalignment defects in the separators supplied during stacking can be prevented. This allows for the manufacture of an electrode assembly with uniform and excellent performance.

[0085] In one embodiment of the present invention, the organic / inorganic composite porous coating layer may have a thickness of 2 μm to 5 μm. When the coating layer is within this thickness range, the separator according to the present invention is more likely to have a desired modulus and kinetic friction coefficient.

[0086] In one embodiment of the present invention, the porous substrate may have a porosity of 20% to 60%, preferably 25% to 55%.

[0087] In one embodiment of the present invention, the porous substrate may have pores with a size of 20 nm to 25 nm.

[0088] In one embodiment of the present invention, the compressibility of the porous substrate may be less than 10%, preferably less than 8%.

[0089] In one embodiment of the present invention, the compressibility was calculated by heating and pressing the porous substrate at a temperature of 70°C and a pressure of 4 MPa for 1 second, and then calculating the change in thickness after heating and pressing, that is, by the following Equation 1:

[0090] [Formula 1] Compressibility (%) = [(porous substrate thickness before heating and pressing - porous substrate thickness after heating and pressing) / porous substrate thickness before heating and pressing] × 100 (%) When the compressibility range is satisfied, the modulus value according to the present invention can be obtained. The compressibility is also called thickness deformation ratio.

[0091] <Secondary battery> One embodiment of the present invention provides a secondary battery that satisfies the following formula 1:

[0092] [Formula 1] X<5mm In the formula 1, X is, after the activation step of the secondary battery, formed by bending the electrode assembly The secondary battery is placed on a flat surface with the concave surface facing up, and two opposing sides of the upper surface of the secondary battery are connected. Gukk The maximum distance measured from the reference line of the battery to the lowest point on the upper surface of the secondary battery. Here, if the degree of depression on the opposing surfaces of the secondary battery is equal, the measurement is made with one of the surfaces facing upward.

[0093] Satisfying Equation 1 means that bending does not occur in the secondary battery after activation. That is, after the activation process of the secondary battery, one side of the secondary battery has a partially concave shape, as shown in Figure 4. In this case, as shown in Figure 4, the secondary battery is placed on a flat surface with the concave side facing up, and the maximum distance from an imaginary reference line connecting two opposing sides of the upper surface of the secondary battery to the lowest point on the upper surface of the secondary battery is measured.

[0094] Specifically, one flat ruler (hereinafter, "ruler a") was placed on each of two opposing sides of the upper surface of the secondary battery, and another flat ruler (hereinafter, "ruler b") was used to measure the maximum distance to the lowest point on the upper surface of the secondary battery. If the maximum distance measured from one side of ruler a to the lowest point on the upper surface of the secondary battery using ruler b is less than 5 mm, it is defined as no bending. According to this definition, (a) in Figure 4 shows a case where bending has occurred, and (b) in Figure 4 shows a case where bending has not occurred.

[0095] In one embodiment of the present invention, the electrode assembly may be free of bending after an activation process, which means that the electrode assembly may be free of bending when removed by opening the battery case after the activation process.

[0096] <Secondary battery manufacturing method> One embodiment of the present invention provides a method for manufacturing a secondary battery that includes a step of activating a secondary battery and satisfies Equation 1. As a result, the method for manufacturing a secondary battery of the present invention can provide a secondary battery that is free from bending after the activation step.

[0097] An example method for manufacturing a secondary battery includes: providing an electrode assembly according to the above embodiment in a battery case; sealing the battery case; injecting an electrolyte into the battery case; and The method includes activating the secondary battery.

[0098] In one embodiment of the present invention, the method for manufacturing a secondary battery may further include laminating the positive electrode, the negative electrode, and the separator before disposing the electrode assembly in the battery case. For example, the lamination may be performed by heating and pressurizing the secondary battery. The heating and pressurizing step may be performed before disposing the electrode assembly in the battery case, by heating the positive electrode, the negative electrode, and the separator at a temperature of 30°C to 90°C, a pressure of 2 MPa to 5 MPa, and a time of 15 seconds to 30 seconds. The heating and pressurizing step is performed before activating the secondary battery and refers to a step other than the heating and pressurizing step in the process of manufacturing an electrode assembly by stacking electrodes and a separator. The lamination step may be performed without a jig (free jig formation). Lamination under such conditions may affect the wet or dry adhesive strength between the separator and the positive or negative electrode. If the lamination conditions are below the above range, it is difficult to obtain the desired dry adhesive strength, making the next step of assembly difficult. Also, if the lamination conditions are above the above range, although the adhesive strength is excellent, it is difficult to control the wetting of the electrolyte, and the adhesive strength of the separator to the positive and negative electrodes becomes unbalanced, which can further worsen bending.

[0099] In one embodiment of the present invention, the activation step of the secondary battery may include degassing after charging one or more times, for example, two or three times, under conditions of 25°C to 60°C, pressure of 0.1 MPa to 0.9 MPa, current of 0.2 C to 0.8 C, e.g., 0.3 C to 0.7 C, 0.4 C to 0.6 C, or 0.5 C, and state of charge (SOC) of 30% to 60%. The conditions of such activation steps may also affect the wet or dry adhesive strength between the separator and the positive or negative electrode. If the temperature during the activation step is too high, the adhesive strength between the positive and negative electrodes may be unbalanced, accelerating bending. If the SOC is less than 30%, a desirable SEI film may not form, and if it exceeds 60%, volume expansion and contraction of the negative electrode may cause bending. The activation step may be performed under pressure using a jig to meet the aforementioned pressure conditions. By carrying out activation while applying pressure with a jig, bending can be minimized even without a jig during charge and discharge conditions after the activation stage. However, excessive pressure can cause problems such as lithium deposition due to binder resistance caused by high adhesion.

[0100] In one embodiment of the present invention, the method for manufacturing a secondary battery may further include manufacturing the electrode assembly before providing the electrode assembly in the battery case. a positive electrode supply stage for supplying positive electrodes to the stack table; a negative electrode supplying step of supplying negative electrodes to the stack table; a separator supplying step of supplying a separator to the stack table; a stacking step of stacking a stack including the positive electrode, the separator, and the negative electrode on the stack table; and The method may include a heat pressing step in which the laminate is heated and pressed.

[0101] According to one embodiment, the separator supply step comprises supplying the separator at a pressure of 0.1 kgf / cm 2 The material may be supplied under pressure.

[0102] In one embodiment of the present invention, the heat pressing step includes a lower plate on which the electrode assembly to be heated and pressed is placed and to which heat can be applied, and an upper plate corresponding to the lower plate and to which heat can be applied. The upper plate and the lower plate may be a pair of pressing blocks.

[0103] In one embodiment of the present invention, the stacking step may include the steps of: supplying the positive electrode to a stack table; supplying the negative electrode to the stack table; and supplying the separator to the stack table.

[0104] That is, the stacking step may further include the steps of: supplying the positive electrode to a stack table; and supplying the negative electrode to the stack table.

[0105] In one embodiment of the present invention, the step of supplying the separator to the stack table includes the steps of: loosening the separator wound around a separator roll; and applying 0.1 kgf / cm 2 The separator may be pressurized by a separator dancer portion, which will be described later.

[0106] The method for manufacturing an electrode assembly according to an embodiment of the present invention may include transferring the stack to a heat press after the stacking step. In order to transfer the stack in the transferring step, the stack may be gripped by a gripper.

[0107] In one embodiment of the present invention, the gripper can maintain grip on the laminate during the heat pressing step, which can be referred to as the first heat pressing step.

[0108] In one embodiment of the present invention, the gripper can stop gripping the laminate during the heat pressing step, which can be referred to as a second heat pressing step.

[0109] Furthermore, in one embodiment of the present invention, the heat pressing step may be performed only once by stopping the clamping of the laminate.

[0110] In one embodiment of the present invention, the step of manufacturing a stack in which positive and negative electrodes are alternately arranged between folded separators may be performed using techniques commonly used in the art. For example, the step may involve stacking positive electrodes on the stack table, covering the positive electrodes with a separator, stacking a negative electrode on top of the separator, folding the separator to cover the negative electrode, and then stacking a positive electrode on top of the separator, repeating this process. This is referred to as a zigzag stacking method in this embodiment. In this case, the step of moving the separator while covering the positive or negative electrode placed on the separator may be performed using a stack table that moves left and right, a separator that moves left and right, or a stack table that rotates.

[0111] In the zigzag stacking method, a holding mechanism holds the stack, thereby maintaining the alignment of the stack while the positive electrode, negative electrode, and separator are stacked.

[0112] In this specification, the term "holding mechanism" refers to a mechanism that grips a stack placed on a stack table in order to stack positive electrodes or negative electrodes in the zigzag stacking method, and is different from the gripper that grips the stack in the heat press stage.

[0113] In one embodiment of the present invention, the separator may be provided in the form of a separator sheet. That is, the additional separator may be provided in a continuous form. Also, the "upper surface" may refer to the surface opposite to the surface on which the separator or electrode is placed on the stack table.

[0114] In an embodiment of the present invention, the heat pressing step may heat the laminate while pressing it in the lamination axis direction. The heat pressing step may be performed by a heat press unit described below.

[0115] Furthermore, in one embodiment of the present invention, the heat pressing step may include the steps of: moving the laminate between a pair of pressure blocks including a press heater; moving the pair of pressure blocks toward each other in the stacking axis direction to apply surface pressure to the laminate; and heating the laminate.

[0116] The pair of pressure blocks may be a lower plate and an upper plate facing the lower plate.

[0117] Furthermore, in one embodiment of the present invention, the heat pressing step may include the steps of: moving the laminate between a pair of pressure blocks; moving the pair of pressure blocks in the lamination axis direction to apply surface pressure to the laminate; and heating the laminate by a separately provided press heater.

[0118] That is, the press heater may be included in the pressurizing block, or may be provided as a separate structure.

[0119] As described above, the method for manufacturing an electrode assembly according to an embodiment of the present invention may further include a step of releasing or loosening the gripper before the heat pressing step. The step of releasing the gripper may include a step of stopping the gripper from pressing the upper surface of the laminate; and a step of moving the gripper away from the laminate.

[0120] In addition, in the heat pressing step, the step of moving the laminate between a pair of pressure blocks including a press heater may include not only moving the laminate itself but also moving the laminate placed on a stack table together with the stack table. In this case, the objects to be heated and pressed by the pair of pressure blocks and the press heater may refer to the laminate and the stack table.

[0121] In one embodiment of the present invention, the heat pressing step may involve heating and pressing the laminate at a temperature of 30°C to 90°C and a pressure of 2 MPa to 5 MPa for 15 to 30 seconds. More preferably, the laminate may be heated and pressed at a temperature of 60°C to 90°C and a pressure of 2.5 MPa to 4.5 MPa for 15 to 30 seconds. More preferably, the laminate may be heated and pressed at a temperature of 65°C to 85°C and a pressure of 3 MPa to 4 MPa for 15 to 25 seconds.

[0122] When the above conditions are satisfied and heating and pressure are applied, the adhesive strength between the positive electrode and the separator and between the separator and the negative electrode can be improved without damaging the positive electrode, the separator, and the negative electrode, thereby improving the performance of the electrode assembly.

[0123] For reference, a semi-finished product state in which a positive electrode, a separator, and a negative electrode are repeatedly stacked can be referred to as a laminate, and a separate component obtained by performing a separator winding process on the semi-finished product can be classified as an electrode assembly.

[0124] Furthermore, one embodiment of the present invention can provide an electrode assembly manufacturing apparatus to which the electrode assembly manufacturing method can be applied.

[0125] Specifically, the electrode assembly manufacturing apparatus according to the present invention may include a separator supply unit that supplies a separator to the stack table; a positive electrode supply unit that supplies a positive electrode to the stack table; and a negative electrode supply unit that supplies a negative electrode to the stack table.

[0126] In one embodiment of the present invention, the heat press unit may be composed of a pair of pressure blocks, and the pair of pressure blocks may move in directions opposite to each other to apply surface pressure to the laminate.

[0127] The heat press unit includes a pair of pressure blocks and a press heater for heating the pressure blocks. While the press heater heats the pressure blocks, the pair of pressure blocks move in directions opposite to each other, thereby applying surface pressure to the laminate placed between the pressure blocks.

[0128] In this case, the pair of pressurizing blocks may include press heaters therein.

[0129] In another embodiment of the present invention, the heat press unit may comprise two separate heat press units, i.e., a first heat press unit and a second heat press unit.

[0130] Referring to FIG. 9, the first heat press unit may include a pair of first pressure blocks. The pressure surfaces of the pair of first pressure blocks may include grooves shaped to correspond to the grippers so that the grippers can press the laminate while gripping the laminate. The pressure surfaces other than the grooves may be flat. The second heat press unit may include a pair of second pressure blocks. The pressure surfaces of the pair of second pressure blocks may be flat. In other words, when the laminate is placed on the pressure surfaces of the pressure blocks, the second pressure blocks can move relative to each other to heat and press the laminate.

[0131] Dividing the heat press section into two sections as described above allows the heated laminate to be cooled while being transported, preventing the adhesive strength between the layers inside the laminate from being lost.

[0132] The conditions for heating and pressing the laminate in the heat press section are the same as those in the heat press step described above.

[0133] The electrode assembly manufacturing apparatus according to the present invention may further include a gripper that grips the laminate during the process of transferring the laminate from the stack table to the heat press unit. The gripper may grip and release the laminate in the above-described manner.

[0134] In this specification, the term "unit" refers to an interface that performs a specific function within an electrode assembly manufacturing apparatus.

[0135] In one embodiment of the present invention, the stack table may include a table body on which a stack body is placed and a drive unit that drives the table body. The table body may include a stack table heater that can heat the stack body to a predetermined temperature when the stack body is placed on the table body.

[0136] In one embodiment of the present invention, the positive electrode supply section may include at least one of a positive electrode mounting table, a positive electrode roll, a first cutter, a first conveyor belt, and a positive electrode supply head.

[0137] Furthermore, the positive electrode mounting table may include a positive electrode heater that heats the positive electrode placed on the positive electrode mounting table to a predetermined temperature.

[0138] In one embodiment of the present invention, the negative electrode supply section may include at least one of a negative electrode mounting table, a negative electrode roll, a second cutter, a second conveyor belt, and a negative electrode supply head.

[0139] Furthermore, the negative electrode mounting table may include a negative electrode heater that heats the negative electrode placed on the negative electrode mounting table to a predetermined temperature.

[0140] In one embodiment of the present invention, the positive electrode stacking unit may include a first suction head that vacuum-sucks the positive electrode mounted on the positive electrode mounting table. The positive electrode can be moved from the positive electrode mounting table to the stack table via the positive electrode stacking unit.

[0141] The negative electrode stacking unit may include a second suction head that vacuum-sucks the negative electrodes mounted on the negative electrode mounting table. The negative electrodes can be moved from the negative electrode mounting table to the stack table via the negative electrode stacking unit.

[0142] In one embodiment of the present invention, the current collector, active material, conductive material, etc. used in the positive electrode and the negative electrode may be any active material known in the art, and the method for manufacturing the positive electrode and the negative electrode may be any method known in the art, without limitation.

[0143] Fig. 6 shows a cross-sectional view of the process flow of an electrode assembly manufacturing apparatus according to one embodiment of the present invention, and Fig. 7 shows a plan view of the process flow of an electrode assembly manufacturing apparatus according to one embodiment of the present invention. For convenience, Fig. 6 omits the holding mechanism 170 and heat press unit 180 shown in Fig. 7, and Fig. 7 omits the separator supply unit 120 shown in Fig. 6.

[0144] 6 to 8, an apparatus 100 for manufacturing an electrode assembly according to an embodiment of the present invention includes a separator supply unit 120 that supplies a separator 14 to a stack table 110, a positive electrode supply unit 130 that supplies a positive electrode 11 to the stack table 110, and a negative electrode supply unit 140 that supplies a negative electrode 12 to the stack table 110. In this case, the separator 14, positive electrode 11, and negative electrode 12 may be heated in the positive electrode supply unit 130 and the negative electrode supply unit 140, respectively, and then supplied to the stack table 110.

[0145] Also, an electrode assembly manufacturing apparatus 100 according to an embodiment of the present invention includes a positive electrode stacking unit 150 that stacks the positive electrodes 11 supplied by a positive electrode supply unit 130 on a stack table 110, and a negative electrode stacking unit 160 that stacks the negative electrodes 12 supplied by a negative electrode supply unit 140 on the stack table 110. In this case, the separators 14 supplied by the separator supply unit 120 are stacked in a zigzag pattern, alternately moving back and forth between the left and right sides of the stacking axis. In this case, the positive electrodes 11 and the negative electrodes 12 are alternately inserted into spaces (between separators) generated by folding the separators 14, resulting in a stack in which the positive electrodes 11, separators 14, negative electrodes 12, and separators 14 are repeatedly stacked on the stack table 110.

[0146] The separator supply unit 120 may include a separator heating unit 121 and a separator roll 122. The separator heating unit 121 is selectively applicable.

[0147] More specifically, the positive electrode supply unit 130 may include a positive electrode mounting table 131, a positive electrode heater (not shown), a positive electrode roll 133, a first cutter 134, a first conveyor belt 135, and a positive electrode supply head 136. The positive electrode heater (not shown) is selectively applicable.

[0148] The negative electrode supply unit 140 may also include a negative electrode mounting table 141, a negative electrode heater (not shown), a negative electrode roll 143, a second cutter 144, a second conveyor belt 145, and a negative electrode supply head 146. The negative electrode heater (not shown) is optional.

[0149] The positive electrode stacking unit 150 stacks positive electrodes 11 on the stack table 110. At this time, the positive electrode stacking unit 150 may include a first suction head 151, a first head heater (not shown), and a first moving unit 153. In addition, the negative electrode stacking unit 160 stacks negative electrodes 12 on the stack table 110. The negative electrode stacking unit 160 may include a second suction head 161, a second head heater (not shown), and a second moving unit 163.

[0150] The positive electrode stack unit 150 and the negative electrode stack unit 160 may further include heaters (not shown) for preheating the positive and negative electrodes, as the case may be.

[0151] Furthermore, the electrode assembly manufacturing apparatus 100 according to an embodiment of the present invention may further include a holding mechanism 170 that fixes the positive electrode 11 and the negative electrode 12 when they are stacked on the stack table 110. Furthermore, the electrode assembly manufacturing apparatus 100 according to an embodiment of the present invention includes a heat press unit 180 that applies heat and pressure to the stack placed on the stack table 110 to bond the positive electrode 11, the separator 14, and the negative electrode 12 together.

[0152] The electrode assembly manufacturing apparatus 100 according to an embodiment of the present invention further includes an induction heating unit (not shown) that inductively heats the laminate and transfers heat to the electrodes in the laminate. The apparatus may also include a control unit (not shown) that controls whether the induction heating unit (not shown) is activated. This allows the electrode assembly 10 shown in FIG. 7 to be manufactured.

[0153] FIG. 8 is a cross-sectional view illustrating an example of an electrode assembly manufactured by an apparatus for manufacturing an electrode assembly and a method for manufacturing an electrode assembly according to an embodiment of the present invention.

[0154] Referring to FIG. 8, the electrode assembly 10 may be formed by stacking separators that are folded in a zigzag pattern and inserting positive and negative electrodes alternately into spaces between the separators.

[0155] In this case, the electrode assembly 10 may be provided in a form in which the outermost corners of the laminate are wrapped with the separators 14. However, the configuration of the electrode assembly 10 is not limited to the example shown in FIG.

[0156] FIG. 9 shows the configuration of a heat press 50, and particularly shows a case where the heat press unit 50 includes a first heat press unit 50 and a second heat press unit 60.

[0157] FIG. 9(a) is a perspective view showing the first heat press unit 50, and FIG. 9(b) is a perspective view showing the second heat press unit 60. As shown in FIG.

[0158] 9(a), the first heat press unit 50 can apply heat and pressure to the laminate S while it is fixed with the gripper 51. The first heat press unit 50 may be composed of a pair of first pressure blocks 50a and 50b. The pair of first pressure blocks 50a and 50b have flat pressure surfaces except for a groove corresponding to the fixing portion 51b of the gripper 51.

[0159] The gripper 51 may include a main body 51a that corresponds to the length x and height y of the stack S or is wider than the length x and height y of the stack S, and a fixing portion 51b that protrudes from the main body 51a and grips the stack S. Here, the length x of the stack S may refer to the longest portion from one end to the other end of the stack S, the height y may refer to the distance in the stacking direction of the stack S, and the width z may refer to the distance across the top surface of the stack S.

[0160] The fixing portion 51b can be adjusted in position along the height direction of the main body 51a, and the fixing portion 51b can contact the upper and lower surfaces of the stack S to fix the stack S.

[0161] Thereafter, the pair of first pressure blocks 50a, 50b move in directions opposite to each other to heat and pressurize the stack S. The heating and pressing stably bond the electrodes and separators inside the electrode assembly.

[0162] The first heat press unit 60 may be a component that complements the cooling of the induction-heated electrode assembly while it is moving, and may be provided as an optional component. That is, it may be omitted in some cases.

[0163] 9(b), the second heat press unit 60 can finally heat and pressurize the laminate S that has been primarily heated and pressed by the first heat press unit 50. The second heat press unit 60 includes a pair of second pressure blocks 60a, 60b that are moved in directions opposite to each other to apply surface pressure to the laminate S. In addition, the pair of second pressure blocks 60a, 60b included in the second heat press unit 60 may all have flat pressure surfaces that come into contact with and pressurize the laminate S. [Example]

[0164] Although the embodiments of the present invention have been described in detail above, the scope of the present invention is not limited thereto, and it will be obvious to those skilled in the art that various modifications and variations are possible within the scope that does not deviate from the technical idea of ​​the present invention described in the claims.

[0165] The physical properties and performance of the separators, electrode assemblies, and secondary batteries prepared in the following examples and comparative examples were measured as follows.

[0166] <Experimental Example 1> - Dry Adhesion Strength Measurement The dry adhesive strength of the electrode assembly to the negative electrode and the dry adhesive strength of the electrode assembly to the positive electrode were measured by cutting a portion of the electrode assembly to a size of 20 mm x 70 mm before immersing the electrode assembly in the electrolyte, and preparing a test specimen in which the positive electrode separator and the negative electrode were stacked. The separator of the test specimen was then peeled from one side of the separator in a 90° peel mode at a rate of 100 mm / min using a tensile tester (UTM equipment). The results are shown in Tables 1 to 3 below.

[0167] <Experimental Example 2> - Wet Adhesion Strength Measurement After the activation process, the electrode assembly of the secondary battery was removed from the pouch exterior material. A portion of the electrode assembly (to be impregnated with electrolyte) was cut into a 20 mm x 70 mm size to prepare a test specimen in the form of a stack of a positive electrode separator and a negative electrode. After preparing the test specimen, the separator of the test specimen was peeled from one side of the separator in a 90° peel mode using a tensile tester (UTM equipment) at a rate of 100 mm / min, and the wet adhesive strength of each electrode assembly was measured. The results are shown in Tables 1 to 3 below. That is, as described above, the dry adhesive strength and wet adhesive strength were measured in the same manner, except for whether the electrode assembly was impregnated with electrolyte or not.

[0168] <Experimental Example 3> - Measurement of separator surface components After the activation process, the electrode assembly of the secondary battery was removed from the pouch exterior. To remove any electrolyte additives or metal salts remaining on the separator surface, the separator was immersed in dimethyl carbonate solvent for 30 minutes and then dried at room temperature for 24 hours. The separator surface was then observed and the surface components were measured according to the method described above. The results are shown in Tables 1 to 3 below.

[0169] <Experimental Example 4> - Bending level measurement After the activation process, the secondary batteries including the electrode assemblies were placed on a flat surface with the concave side facing up. A flat ruler (hereinafter, "ruler a") was then placed on the secondary battery to correspond to an imaginary reference line connecting two opposing sides of the upper surface of the secondary battery. Using another flat ruler (hereinafter, "ruler b"), the maximum distance to the lowest point on the upper surface of the secondary battery was measured. The results are shown in Tables 1 to 3 below. For reference, if the measured distance was less than 5 mm, it was defined as no bending.

[0170] <Experimental Example 5> - Separator resistance after activation After the activation process, the electrode assembly of the secondary battery was removed from the pouch exterior material, and then the separator was immersed in dimethyl carbonate solvent for 30 minutes to remove any electrolyte additives or metal salt components remaining on the separator surface. The separator was then dried at room temperature for 24 hours, and its resistance characteristics were then checked.

[0171] Specifically, the separator was cut and stacked in a Hoshen 2032 coin cell, and the resistance value when impregnated with the electrolyte was measured by EIS (Electrochemical Impedance Spectroscopy) at 25°C using an AC method with a 1M LiPF6-ethylene carbonate / ethyl methyl carbonate (weight ratio 3:7) electrolyte, and the results are shown in Tables 1 to 3 below.

[0172] <Experimental Example 6> - Measurement of separator modulus and coefficient of kinetic friction The modulus of the separator was measured. Specifically, a separator test piece 15 mm wide and 15 cm long in the MD direction of the separator was prepared, and a tensile test was performed on the separator test piece using a Universal Testing Machine (UTM). More specifically, the speed condition of the Universal Testing Machine was set to 50 mm / min, and the test was performed, and the modulus was measured at the load applied when the separator test piece was deformed by 2% in the longitudinal direction.

[0173] Separator test pieces measuring 5 cm in width and 5 cm in length in the MD direction of the separator were prepared and measured using a Heidon 14FW friction / wear tester. The friction / wear tester used a 0.1 mmR diamond pin to measure the kinetic friction coefficient for the separator under conditions of a weight of 5 g and a speed of 50 mm / min.

[0174] <Experimental Example 7> - Evaluation of shrinkage rate The separator was evaluated by measuring its thermal shrinkage. Specifically, when the thermal shrinkage of the separator was measured at 130°C, if a thermal shrinkage of more than 5% was observed in either the MD or TD direction, the separator was judged to be defective and in a poor condition.

[0175] <Experimental Example 8> - Evaluation of assembly process The electrode assembly was evaluated for the presence or absence of separator wrinkles and the degree of distortion of the stack (meandering). Specifically, the presence or absence of separator wrinkles in the electrode assembly was determined by disassembling the electrode assembly and visually inspecting the internal separator for wrinkles. If even one wrinkle was found, the electrode assembly was judged to be defective. The electrode assembly was also evaluated for meandering by visually inspecting the edge of the separator located in the electrode tab portion of the electrode assembly. If the edge of the separator was distorted by 1 mm or more, the electrode assembly was judged to be defective.

[0176] Example 1 <Manufacturing of electrode assembly> To manufacture the negative electrode, a mixture of artificial graphite as a carbon-based active material, a binder polymer (SBR (styrene-butadiene rubber) and CMC (carboxymethyl cellulose)), and carbon black as a conductive material in a weight ratio of 95.5:3:1.5 was mixed with water as a dispersant in a weight ratio of 1:2 to prepare a slurry for the first active material layer.

[0177] A silicon oxide with a Coulombic efficiency of 80% or more when charged and discharged at 0.1 C was used as the silicon-based active material. A slurry for the second active material layer was prepared that was identical to that for the first active material layer, except that the silicon-based active material was mixed with a carbon-based active material (artificial graphite) in a weight ratio of 9:1, and carbon nanotubes were added as a conductive material. That is, the weight ratio of the active material, binder polymer, carbon black, and carbon nanotubes (CNTs) was 95.5:3:1.0:0.5, and the weight ratio of the carbon-based active material to the silicon-based active material in the active material was 9:1.

[0178] The specific surface area of ​​the carbon nanotube (CNT) is 550m2 / g The carbon nanotubes (CNTs) were multi-walled carbon nanotubes.

[0179] Using a double slot die, the slurry for the first active material layer was coated on one side of a copper (Cu) thin film, which was a 10 μm-thick negative electrode current collector. Then, the slurry for the second active material layer was coated on the slurry for the first active material layer, and the coating was dried at 130° C. under vacuum for 1 hour to form a first active material layer and a second active material layer.

[0180] The first and second active material layers thus formed were simultaneously rolled using a roll pressing method to fabricate a negative electrode. The thickness ratio of the first and second active material layers was 1:1. The loading amount of the first and second negative electrode active material layers was 512 mg / 25 cm based on the dry weight. 2 (Total thickness of the negative electrode on a dry basis: 292 μm).

[0181] Next, to manufacture the positive electrode, Li(Ni 0.3 Mn 0.5 Co 0.2 A positive electrode active material slurry was prepared by adding N-methylpyrrolidone (NMP) as a solvent to prepare a cathode active material slurry containing 02 (NCM-352), carbon black as a conductive material, and polyvinylidene fluoride (PVdF) as a binder in a weight ratio of 96:2:2. The slurry was coated on one side of an aluminum current collector with a thickness of 15 μm, and then dried and rolled under the same conditions as the negative electrode to prepare a cathode. In this case, the loading amount of the cathode active material layer was 988 mg / cm based on the dry weight. 2 (Total thickness of the positive electrode on a dry basis: 242 μm).

[0182] Finally, a porous substrate, polyethylene film (PE, 9 μm thick), was prepared for the separator. The porous substrate was stretched 8 times in the MD direction at 100°C and 8 times in the TD direction at 125°C. The porous substrate was heated and pressed at 70°C and 4 MPa for 1 second, and the thickness change after heating and pressing was calculated to obtain a compression ratio of 5%.

[0183] Then, a first binder and a second binder were added to distilled water at room temperature to a weight ratio of 60:40 as particulate binders. Next, a dispersant was added to the distilled water along with inorganic particles (weight ratio of the first and second binders to the inorganic particles = 20:80) in a ratio of 4 times the total weight of the first and second binders. The first binder was a styrene-butyl acrylate copolymer with a glass transition temperature (Tg) of 45°C, obtained by adjusting the weight ratio of the two monomers (styrene and butyl acrylate) to 70:30. The second binder was a PVDF-HFP binder with a content of 5 wt% HFP-derived repeating units.

[0184] The inorganic particles used were Al2O3, and had an aspect ratio of 1 to 10 and a D50 of 0.5 μm.

[0185] Then, 0.7 μm zirconia beads were added to the distilled water in the same amount as the inorganic particles, and the mixture was bead milled using a paint shaker for 2 hours to prepare an inorganic dispersion.

[0186] Next, a surfactant was further added to the inorganic dispersion, and the inorganic dispersion was stirred at 10 rpm for 10 minutes to prepare a slurry in which the binder and inorganic particles were dispersed.

[0187] The slurry was then coated on both sides of the polyethylene film (PE, 9 μm thick) using a doctor blade and dried using a hot air blower to form porous coating layers with a thickness of 2.5 μm, thereby producing a separator of Example 1 with a total thickness of 14 μm. The modulus of the produced separator was 6,000 (kgf / cm 2 ) and the coefficient of kinetic friction was 0.25.

[0188] The fabricated positive electrodes, negative electrodes, and separators were fed to a stacking table, and the separators were folded to stack the positive electrodes, negative electrodes, and separators. Specifically, the positive electrodes and negative electrodes were stacked on the stacking table in a manner that alternated between the folded separators, to fabricate a stack using 39 electrodes. The stack was then heated and pressurized at a temperature of 60°C and a pressure of 3 MPa for 15 seconds (time condition) to fabricate the electrode assembly of Example 1.

[0189] <Secondary battery manufacturing> The electrode assembly of Example 1 was placed in a pouch exterior material (battery case) of CPP / aluminum / nylon laminate sheet, and an ethyl methyl carbonate electrolyte solution containing LiPF6 was injected. The pouch exterior material was then heat-sealed to complete the assembly of the secondary battery.

[0190] Thereafter, the secondary battery was subjected to an activation step in which the secondary battery was charged at 0.5 C up to SOC 50% under the conditions of a temperature of 50° C. and a pressure of 0.5 MPa.

[0191] Example 2 The separator was produced in the same manner as in Example 1, except that the first binder and the second binder were added as particulate binders in a weight ratio of 50:50.

[0192] Comparative Example 1 The separator was produced in the same manner as in Example 1, except that the first binder and the second binder were added as particulate binders in a weight ratio of 15:85.

[0193] Comparative Example 2 The separator was produced in the same manner as in Example 1, except that the first binder and the second binder were added as particulate binders in a weight ratio of 70:30.

[0194] Comparative Example 3 The separator was prepared in the same manner as in Example 2, except that the first binder, a copolymer of styrene and butyl acrylate, was used in which the weight ratio of the two monomers (styrene and butyl acrylate) was adjusted to 25:75.

[0195] Comparative Example 4 The separator was prepared in the same manner as in Example 2, except that the first binder, a copolymer of styrene and butyl acrylate, was used in which the weight ratio of the two monomers (styrene and butyl acrylate) was adjusted to 85:10.

[0196] Comparative Example 5 The separator was prepared in the same manner as in Example 2, except that a PVDF-HFP binder containing 1.5 wt % of repeating units derived from HFP was used as the second binder.

[0197] Example 3 The separator was prepared in the same manner as in Example 2, except that a PVDF-HFP binder containing 20 wt % of repeating units derived from HFP was used as the second binder.

[0198] Comparative Example 6 The separator was manufactured in the same manner as in Example 2, except that inorganic particles having an aspect ratio of 11 were used.

[0199] Comparative Example 7 The same procedure as in Example 2 was carried out, except that the laminate of the positive electrode, negative electrode, and separator was heated and pressurized at a temperature of 20°C and a pressure of 1 MPa instead of at a temperature of 60°C and a pressure of 3 MPa.

[0200] Comparative Example 8 The same procedure as in Example 2 was carried out, except that the laminate of the positive electrode, negative electrode, and separator was heated and pressurized at a temperature of 80°C and a pressure of 6 MPa instead of at a temperature of 60°C and a pressure of 3 MPa.

[0201] Comparative Example 9 The activation process of the secondary battery was carried out under a charged state (SOC 25%) and a pressure of 0.3 kgf / cm 2 The procedure was the same as in Example 2, except that the pressure was 1000 kJ / min.

[0202] Comparative Example 10 The activation process of the secondary battery was carried out under a charged state (SOC 80%) and a pressure of 10 kgf / cm 2 The procedure was the same as in Example 2, except that the pressure was 1000 kJ / min.

[0203] Comparative Example 11 When manufacturing the separator, the porous substrate is stretched 6 times in the MD direction at 100°C and 5.5 times in the TD direction at 125°C, resulting in a modulus of 2,000 (kgf / cm 2 The procedure was the same as in Example 1, except that

[0204] Comparative Example 12 When manufacturing the separator, the porous substrate is stretched 11 times in the MD direction at 100°C and 10 times in the TD direction at 125°C. The modulus of the separator is 10,000 (kgf / cm 2 The procedure was the same as in Example 1, except that

[0205] Comparative Example 13 The separator was prepared in the same manner as in Example 1, except that the weight ratio of the first and second binders to the inorganic particles in the slurry was 10:90, and the kinetic friction coefficient of the prepared separator was 0.1.

[0206] Comparative Example 14 The separator was prepared in the same manner as in Example 1, except that the weight ratio of the first and second binders to the inorganic particles in the slurry was 60:40, and the kinetic friction coefficient of the prepared separator was 0.4.

[0207] [Table 1]

[0208] [Table 2]

[0209] [Table 3] In Tables 1 to 3, the positive electrode adhesive strength means the adhesive strength of the separator to the positive electrode, and the negative electrode adhesive strength means the adhesive strength of the separator to the negative electrode.

[0210] In Examples 1 and 2, it was confirmed that the electrode assemblies of Examples 1 and 2 did not bend because the separators had appropriate wet adhesive strength and dry adhesive strength to the negative and positive electrodes.

[0211] In Comparative Examples 1, 3, and 4, the dry adhesion of the separator to the negative or positive electrode was too low to proceed with the electrode assembly manufacturing process, and therefore the wet adhesion of the separator could not be measured. In Comparative Example 1, an excessive amount of fluoropolymer was used in the separator coating layer, while in Comparative Examples 3 and 4, the content of the acrylic polymer comonomer in the separator coating layer was varied. In Comparative Example 3, the Tg of the acrylic copolymer was low, causing it to melt during processing. In Comparative Example 4, the Tg of the acrylic copolymer was too high, resulting in too low dry adhesion to the negative electrode, which reduced assembly processability and prevented processing.

[0212] As described in the results of Experimental Examples 7 and 8, in Comparative Examples 11 to 14, it was impossible to fabricate an electrode assembly, and the wet adhesive strength after fabrication of the electrode assembly could not be measured. In Comparative Example 11, wrinkles occurred during the zigzag stacking process due to the low elastic modulus of the separator, and in Comparative Example 12, the separator had a shrinkage rate of 50% or more, resulting in poor meandering. In Comparative Example 13, slippery occurred between the separator and the electrode due to the use of a separator with an excessively small coefficient of kinetic friction, and in Comparative Example 14, poor meandering occurred during separator travel due to excessive friction during the process due to the use of a separator with an excessively large coefficient of kinetic friction.

[0213] In Comparative Examples 2, 5, 7 and 9, the wet adhesive strength of the separator to the negative electrode or positive electrode was too low, causing overhang in the laminate, and the edge portions drooping when the cell was lifted.

[0214] When the separator slurry dries, the low-specific-gravity binder must migrate to the surface, and this is easily achieved when the inorganic particles have a uniform shape. However, in Comparative Example 6, the inorganic particles with a large aspect ratio were randomly distributed, which hindered the binder from migrating to the surface due to the interference of the particles during drying of the slurry (reduced binder migration). As a result, the dry adhesive strength of the separator to the positive electrode and the wet adhesive strength of the separator to the negative electrode were very low.

[0215] In Comparative Examples 8 and 10, the wet adhesive strength of the separator to the negative electrode was excessively high, and a high bending level was observed.

[0216] Therefore, the electrode assembly of the present application does not undergo bending, and as a result, the electrodes can be aligned and fixed without shifting, and the energy density can be improved, thereby demonstrating excellent performance of the electrode assembly and the secondary battery including the same.

[0217] As shown in Fig. 10, it was confirmed that the electrode assembly of Example 1 did not have wrinkles in the separator, while the electrode assembly of Comparative Example 14 had wrinkles in the separator, as shown in Fig. 11. In Fig. 11, a horizontal line appears in the middle, and this line is a wrinkle.

[0218] 12, it was confirmed that the separator edges of the electrode assembly of Example 1 were well aligned (the separator edges were not misaligned by 1 mm or more). On the other hand, it was confirmed that the separator edges of the electrode assembly of Comparative Example 11 were not well aligned, being misaligned by 1 mm or more, as shown in FIG. 13. This is believed to be caused by meandering of the separators supplied during the manufacturing process of the electrode assembly of Comparative Example 11. [Explanation of symbols]

[0219] 1 Porous substrate 2. Organic / inorganic composite porous coating layer 3 Inorganic particles 4. Fluorine-based polymers 5. Acrylic polymers 10 Electrode assembly 11 Positive electrode 12 Negative electrode 14 Separator 51 Gripper 51a Main unit 51b Fixed part 100 Electrode assembly manufacturing apparatus 110 Stack Table 120 Separator supply section 121 Separator heat section 122 Separator roll 130 Positive electrode supply unit 131 Positive electrode mounting table 133 Positive electrode roll 134 First Cutter 135 First Conveyor Belt 136 Positive electrode supply head 140 negative electrode supply unit 141 Negative electrode mounting table 143 Negative electrode roll 144 Second Cutter 145 Second Conveyor Belt 146 Anode supply head 150 Positive electrode stack section 151 First Suction Head 153 First Mobile Unit 160 negative electrode stack section 161 Second Suction Head 163 Second Mobile Unit 170 Holding mechanism 171 First holding mechanism 172 Second holding mechanism 180 Press Department 181 (50a, 50b) First pressure block 182 (60a, 60b) Second pressure block S laminate

Claims

1. An electrode assembly including a positive electrode, a negative electrode, and a separator disposed between the positive electrode and the negative electrode, The separator is A porous substrate and an organic / inorganic composite porous coating layer provided on at least the negative electrode side surface of the porous substrate, the organic / inorganic composite porous coating layer provided on the negative electrode side includes a particulate binder resin and inorganic particles; the particulate binder resin contains an acrylic polymer and a fluorine-based polymer, The organic / inorganic composite porous coating layer provided on the surface of the negative electrode contains 0.1 to 8 parts by weight of fluorine (F) per 100 parts by weight of the surface component, The electrode assembly, wherein the separator has a wet adhesive strength to the negative electrode of 1.5 gf / 20 mm or more and 15 gf / 20 mm or less.

2. The electrode assembly of claim 1 , wherein the separator has a dry adhesive strength to the negative electrode of 8 gf / 20 mm or more and 25 gf / 20 mm or less.

3. The electrode assembly of claim 1 , wherein the separator has a wet adhesive strength to the negative electrode of 4 gf / 20 mm or more and 6 gf / 20 mm or less.

4. The electrode assembly of claim 1 , wherein the wet adhesive strength of the separator to the negative electrode is at least one time greater than the wet adhesive strength of the separator to the positive electrode.

5. The electrode assembly of claim 1 , wherein the wet adhesive strength of the separator to the negative electrode is 1 to 1.4 times the wet adhesive strength of the separator to the positive electrode.

6. The electrode assembly of claim 1 , wherein the negative electrode comprises a silicon-based active material.

7. 2. The electrode assembly according to claim 1, wherein the overall length is 400 mm to 600 mm and the overall width is 50 mm to 150 mm.

8. An electrode assembly as described in claim 1, wherein the weight ratio of the acrylic polymer to the fluoropolymer is 20:80 to 60:

40.

9. The modulus of the separator measured in the separator feed direction (MD; Machine Direction) is 4,000 kgf / cm ２ Above, 10,000kgf / cm ２ 2. The electrode assembly according to claim 1, wherein the separator has a coefficient of kinetic friction of more than 0.1 and not more than 0.

35.

10. 2. The electrode assembly of claim 1, wherein the acrylic polymer has a glass transition temperature (Tg) of 40 to 60.degree.

11. the acrylic polymer is a (meth)acrylic acid ester-styrene copolymer, 2. The electrode assembly of claim 1, wherein the styrene is contained in an amount of 50 to 80 parts by weight based on 100 parts by weight of the comonomer constituting the acrylic polymer.

12. the fluoropolymer is a copolymer of vinylidene fluoride and hexafluoropropylene (HFP) (PVdF-HFP), 2. The electrode assembly of claim 1, wherein the hexafluoropropylene is present in an amount of 3 to 18 parts by weight based on 100 parts by weight of the comonomer constituting the copolymer (PVdF-HFP).

13. The electrode assembly of claim 1 , wherein the inorganic particles have a non-rectangular structure.

14. The electrode assembly according to claim 1 , wherein the separators are stacked by being folded in a zigzag pattern.

15. a sealed battery case; The electrode assembly according to any one of claims 1 to 14 is contained inside the battery case; an electrolyte contained inside the battery case; Including, A secondary battery that satisfies the following formula 1: [Formula 1] X<5mm In the formula 1, X means the maximum distance measured from an imaginary reference line connecting two opposing sides of the upper surface of the secondary battery to the lowest point of the upper surface of the secondary battery when the secondary battery is placed on a flat surface with the concave surface of the secondary battery formed by bending the electrode assembly facing up after the activation process of the secondary battery.

16. Providing the electrode assembly according to any one of claims 1 to 14 in a battery case; sealing the battery case; injecting an electrolyte into the battery case; Activating the secondary battery Including, A method for manufacturing a secondary battery, which satisfies the following formula 1: [Formula 1] X<5mm In the formula 1, X means the maximum distance measured from an imaginary reference line connecting two opposing sides of the upper surface of the secondary battery to the lowest point of the upper surface of the secondary battery when the secondary battery is placed on a flat surface with the concave surface of the secondary battery formed by bending the electrode assembly facing up after the activation process of the secondary battery.

17. 17. The method of claim 16, further comprising laminating the positive electrode, the negative electrode, and the separator under conditions of a temperature of 30° C. to 90° C., a pressure of 2 MPa to 5 MPa, and a time of 15 seconds to 30 seconds, before the step of providing the electrode assembly in the battery case.

18. 17. The method of claim 16, wherein activating the secondary battery comprises charging the secondary battery at least once under conditions of a temperature of 25° C. to 60° C., a pressure of 0.1 MPa to 0.9 MPa, a current of 0.2 C to 0.8 C, and a state of charge (SOC) of 30% to 60%, followed by degassing.

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